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Capteur astrophoto
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Why using a high resolution sensor in Astrophotography?

In astrophotography, the camera’s sensor is a key element which needs special attention while choosing your equipment. This rectangular component is about the size of a fingernail and can contain several million of pixels made for converting photons coming from the stars into an image. Compared to the human eye, a sensor is able to detect far fainter objects and can see their actual colors. On the market, reams of sensors are used, all of them having their own dedicated application: webcam, smartphone sensor, DSLR sensor… For instance, the Stellina smart telescope is fitted with a 6.4 MP sensor covering deep sky and lunar imaging. Why is it necessary to choose a high resolution sensor for astrophotography like the one Stellina integrates?

 

A resolution to fit with your devices’ screens

The most widespread sensors have pretty bad resolutions, ranging from 0.3 to 1.3 Mega pixels. Such sensors are made to equip devices where image quality is not a big deal: webcam, front camera of smartphones or tablets.

For a picture to be pin point sharp on a Full HD screen, its definition should be at least 1920 x 1080 pixels, namely around 2.07 MP. Breaking this rule, the quality of a 1.3 MP resolution image displayed on a Full HD screen will be extremely low since the celestial objects will be pixelated. A zoom in will damage even more the quality, which is not conceivable when we know that, nowadays, FHD is the minimum resolution required.

The IMX 178 Sony sensor of the Stellina telescope was chosen on purpose to display nice-looking stills on an Ipad or even on an Ipad Pro without loosing quality! Provided with a 6.4 MP resolution, equivalent to 3086 x 2076 pixels, the sensor is able to capture photos of galaxies, nebulae, star clusters and our natural satellite: the Moon. Such a comfortable number of pixels guarantees an optimized experience for viewing your own images on most of your devices, smartphones, tablets as well as TV.

 

Sharper details and the ability to crop

Owning a high resolution sensor allows you to increase drastically the overall details of the celestial object you captured. If the sensor you are using is more resolved than a Full HD display, a crop on that picture should give simultaneously a close-up view and an identical amount of sharpness. The example below simulates the evolution of the image quality according to four different sensor resolutions applied to an image of the North America nebula – NGC 7000.

A high-performance sensor

Stellina integrates a sensor specifically designed for astronomy, enabling a sensitivity in the near-infrared part of the electromagnetic spectrum, added to the common visible domain. Indeed, a lot of deep sky targets like the Laguna nebula, Orion nebula, Soul nebula, Heart neabula emit a pretty large amount of infrared light. This extended sensitivity increases the light collected by the sensor, rising the intensity of the signal which keeps reducing the disturbing digital noise. Another interesting feature of the sensor: its light pollution filtering or CLS filter (City Light Suppression). This optical filter installed just in front of the sensor often makes urban space enthusiasts happier since it eliminates the typical coloration of the sky caused by artificial lighting: a must have tool, especially nowadays, when the environement has never been so light polluted by human’s activities, degrading the natural darkness of the night sky.

> Read our article listing the impacts of light pollution on astronomy and on our environment. 

Light pollution Dubai
Blog

Why do the stars disappear ?

“Turn off the lights, light on the stars !” is the purpose of the french national movement “The Day of the Night” aiming to raise awareness of the impacts of the light pollution among the general public. The surge of artificial light is indeed being questionable on our health, wild life but also on astronomical observation.

More than 400 activities are scheduled to take place within the french territory, during the night from the 13th to the 14th October 2018.

Light pollution is made of all kind of disturbing light sources whose origin comes from human activity (street lights, commercial signs, advertisement…etc). Currently, 99 % of the European and American population is living under light polluted skies. In the same way as the sound disturbance or the pollution as a whole, it produces reams of discomfort, especially as far as night-time observing is concerned. A recent scientific study has proved that more than a third of the global population can not see the milky way anymore.

What are the effects of light pollution on astronomy?

The light throughput generated by a city or a town does not spread itself exactly where it is meant to. An excessive amount of that light is projected towards the sky, forming a huge diffusive orange or blue halo depending on the primary type of light source used within the area. Whether inside these urban areas or in suburbs, the adjective “dark sky” seems to be obsolete, on grounds of this blurred veil disabling any contrasted view of the stars. Consequently, it becomes pretty hard to spot the stars and the constellations since the cities’ glow are decreasing the luminosity threshold –  called magnitude – our eyes are capable of reaching.

In a totally light-pollution-free sky, 6.5 is the limit magnitude our eyes can detect without help of any sorts of optical instruments. In other words, theoretically 2 500 stars of our sky would be accessible to the naked eye. In most of the cities, though, the magnitude over the one stars are being hidden because of light pollution drops down to 4.0 or 3.0. In these harsh conditions, only 300 or 200 stars are visible except in the heavy populated urban areas like Paris, London, New York, Hong Kong where around 30 stars and less are still shining.

Light pollution before after

Comparison of a heavy polluted sky (left) and a starry sky right after a blackout occurred (right). Images by Todd Carlson. Source : IDA

Keen amateur astronomers are the main victims of the rise of light pollution. Even today, professional astronomers observing through state-of-the-art telescopes are concerned by the over use of lighting, like in Chile.

How can we prevent light pollution from getting worse?

The main cause of visual disturbance can be explained by a high amount of useless lighting. Advertisement panels, empty parking slots, front store… typically are the types of lights mentioned as unnecessary.

An improvement in terms of light distribution and orientation could permit decreasing unwanted light glow over the towns, as long as a middle-ground to insure the security of customers and pedestrians is found.

Received idea: Shifting from orange sodium vapor lamps to LEDs does not mean to decrease light pollution. LEDs emit white light which affects a wider range of the visible light spectrum. Plus, they have usually an emission peak located in the blue which unfortunately fits with the main color of our night deep sky objects.

Light pollution in the US

Current situation of light pollution in North America. Source : Science Advances

For years, a couple of associations advocating the protection of the sky have born such as the ANPCEN in France or the International Dark Sky Assocation (IDA) at a global scale. With the support of local authorities, they could end up adopting a law dealing with regulation of the french public lighting : since the 1st July 2018, front stores and advertisement signs must be turned off from 1:00 am to 6:00 am. This measure should avoid wasting 1000 GWh per year which represents a money saving of about 100 millions euros, or even the consumption of electricity of 370 000 households for a year.

France is in a good way of ecological awareness, whereas 30% of the overall lighting in the United States are estimated to be useless and wasted, raising the money-loss to 3.3 B$ per year.

 

Stellina refractor telescope
Blog, Products

Reflector vs. Refractor telescopes

What is a telescope? This question could seem trivial but behind this universal word, we find two main types of instruments to observe the tremendous objects of our starry sky. The reflector telescopes are composed of mirrors whereas the refractor telescopes are only made of lenses. They are a lot of differences between both of these categories, in terms of performances, durability and especially optical quality.

Reflector telescopes

Principle of a reflectorReflector telescope

The newton telescopes are the most widespread reflectors in the market because of their easy building process and their low cost. The light coming from a star goes inside the optical tube and is first reflected on the primary mirror, located at the extremity. This primary mirror is the master piece of the reflector. It has to collect and make the light beams converging towards the eyepiece holder, the element where we put our eyes. Here, it is necessary to find a way to make the light beams going out of the tube. Therefore, a secondary mirror is installed next to the front aperture of the telescope, enabling beams to be deviated on the side of the telescope, and so, to observe an image.

The asset of a reflector is its primary mirror’s very large size. The bigger the mirror is, the brighter the objects appear in the eyepiece. However, a big mirror could quickly emphasize the optical aberrations of the telescope.

Optical quality of reflectors

Theoretically, getting a perfect round dot of a star requires having a newtonian reflector made with a hyperbolic primary mirror. In fact, such a mirror is relatively expensive and telescopes manufacturers choose rather a parabolic mirror instead, far simpler to build. However, a parabolic mirror is facing a defect: the coma aberration which deforms and elongates the star around the fields of view.

More often, the low-cost manufacturers do not use nor a hyperbolic neither a parabolic mirror but a spherical mirror. With such a geometry, you will never manage to focus perfectly the image of a star with your reflector, because of spherical aberration ; a delicate situation considering that astronomy requires to observe and photograph faint and diffuse celestial objects.

Reflectors in practice

Reflector telescopes are mainly open telescopes, meaning that the mirrors are exposed to the air, humidity and dust. This is why they require to be manipulated with precision and attention. For example, a mirror frequently exposed to this harsh environment could be less reflective within years, or put it in a different way, its ability to reflect light decreases. To this point, the cleaning of the mirror is highly recommended, paying extreme attention to the fragile optical parts while dismounting the telescope.

A key element not to be forgotten with a newtonian-like telescope is the necessity to collimate it. The collimation is a process which consists on adjusting the perfect alignment of the primary and secondary mirrors of the telescope. This should be ideally carried out each time you observe or start an astrophotography session.

Finally, reflector telescopes are first choice instruments when you want to collect the most light as possible. But the side effects are that you will need to know in details the optical system and should not be shy when you will have to modify or clean the mirrors, as mentioned above.

Pros & Cons

Pros

Cons

  • Large mirror = better light collecting capacity
  • No chromatic aberrations (colored fringes around stars)
  • Relatively low cost
  • Optical quality often disappointing
  • Collimation and mirrors cleaning processes
  • Open tube = high vulnerability to dust, humidity..etc
  • Bulky and heavy

Refractor TelescopesRefractor telescope

The principle of keplerian telescope is very similar to a monocular. The light goes through the front lens, key element making the light beams

converging to the eyepiece holder, where we install an eyepiece or a camera.
Because of their compactness and ligthness, refractor telescopes do not collect as much light as reflector but have a more stable optical quality and do not need any adjustement from the user/observer.

Optical Quality of the reflectors

They have the specificity to let us observing the starry sky with an amazing sharpness and contrast. These features are really appreciated in astronomical observation and astrophotography.
Nonetheless, keep attention on what type of refractor you choose. The cheapest are made of a single lens which undergoes the light dispersion. Consequently, a star will not be a single color point anymore but surrounded by colored rings. This is what we call chromatic aberrration.

Today, there are different manners to get rid of this optical defect such as adding a second lens to obtain a Doublet telescope.

Stellina : a refractor inspired by astrophotographersStellina

Most of amateur astrophotographers prefer a telescope whose durability, compactness and simplicity to use are better than the amount of light collected. Therefore they choose refractor telescopes rather than reflectors.

Vaonis has responded to this demand and built a refractor telescope from scratch, helped by one of the most reknown metrology laboratory in France : AiryLab.

The optical design is a Lanthane ED Doublet, permitting to decrease drastically chromatic aberration. A special treatment on the lenses has been applied in order to select only the wavelength of interest and reject all ultraviolet and infrared lights.

All these optimizations brought into this telescope are just contained in a small, transportable and entirely automated refractor. Refractors are thus a reliable choice for stargazers who want a dependable, pratical and easy-to-use astronomical instrument.

Pros & Cons

Pros

Cons

  • Impressive contrast and sharpness
  • Light and transportable
  • Closed tube = protection against humidity and dust
  • Maintenance and cleaning almost nonexistent
  • Small diameter = less light collected
  • Chromatic aberrations
  • Higher price
Milky Way by Astroguigeek
Blog

Guide for Milky Way Photography

Photographing the milky way

Is there something more beautiful than observing the Milky Way in the summer nights? On the same occasion, why not immortalizing this moment by capturing it? As a matter of fact, it has never been as simple and as fast as today to capture the stars. If you think that only expensive or professional material will allow you to capture amazing pictures of the night sky, don’t believe it. With the technological development, the Milky Way can now be photographed with standard consumer cameras and even our smartphones!

How to capture the Milky Way in 2018? Welcome in this 3.0 tutorial, updated and accessible to everybody.

Milky Way France Astroguigeek

The Milky Way taken from the Pic du Midi (France). 15 seconds at ISO 3200, 18 mm, f/1.8. Credit: AstroGuigeek Photographie

Mandatory Equipment

Before getting in depth, it is still useful to know what you will need to take pictures of the starry sky. Few equipment are actually required:

  • A camera equipped with a Manual Mode called mode “M”: nowadays, most of the camera embed this feature and our smartphones too. Look for the “Pro Mode” or the Manual Mode inside the camera app on your device.
  • A standard lens: for DLSR or mirrorless cameras, a 18-55 mm kit lens is enough to photograph the Milky Way.
  • A tripod or camera mount: The tripod is absolutely necessary to make your camera steady and avoid the vibrations caused by motion. Not to forget that small tripods or smartphone tripod adapters can also be purchased.

A short journey in our Galaxy

The galaxy in which the Earth, the Sun and other 250 billion stars are evolving in is called the Milky Way. In addition to this very high numbers, it is made of other components such as molecular clouds and interstellar dusts, giving this multicolored and milky structures in the night sky.

Theoretically, all the stars that our eyes can see are belonging to our galaxy. It will be correct therefore to consider that the whole sky is the Milky Way. Nonetheless, we call Milky Way the strip-shaped structure in which are concentrated most of the stars, interstellar clouds and nebulae.

Because we are located inside our own galaxy, we cannot see its global shape, for which we know that is a spiral. However, we can actually admire a tremendous slice view of the Milky Way. In the night sky we do see this long bright strip displaying shining and dark regions. The Milky Way is even far brighter when our eyesight is pointing towards the galactic center rather than towards the outskirts.

Milky Way France Astroguigeek

The Milky Way as seen from cities outskirts. 45 seconds at ISO 3200. 18 mm, f/1.8. Tracking mount to compensate Earth’s rotating motion

The Milky Way is easily visible with the naked eye from countryside or any other remote areas, far away from towns and cities. Its low brightness makes it hard for our eyes to see the whole picture. Indeed, our eyes can only observe a maximum of 6 000 stars, which is a very small part of our galaxy. Today, sensors from our DSLR or mirrorless or smartphones cameras manage to photograph stunning results and can multiply our eyes capabilities. Besides, they can capture the true colors of the Milky Way whereas our eyes cannot!

How to capture the Milky Way?

Obviously, digital cameras are not able to shoot the Milky Way instantly like a daylight scene helped by sunlight. Stars and clouds of gas are emitting a very few amount of light. To counter this darkness, it is necessary to take a picture lasting several seconds at least.
In the meanwhile, the sensor will record all the light emitted by the stars and will add it up to make the stars more visible and so the Milky Way.

Before getting into the typical camera settings you will need, ensure that you have full access to the camera settings through the manual mode (“M” Mode). This feature enables to set manually every parameter of the picture. Below are the different settings we will modify:

Focal Length ou Zoom

It is important to choose the widest field of view as possible and not to use a zoom. Adjust your lens (for digital cameras) to its smallest focal length value (24 mm, 18 mm, 14 mm or lower). The wider the field of view will be, the more visible the Milky Way will be.

Aperture or F/D ratio

One the most fundamental settings is the lens aperture. This number gives indication about the size of the front lens used. In photography, the aperture is expressed by the “F/D” ratio. Of course, this value is not fixed and can be modified. Here, we want to collect as much light as possible. The lower the aperture is (F/3.5, F/2.8 or F/1.8 …), the more light is passing through the lens. Consequently, the ideal is to let your lens wide open.

Exposure Time

As mentioned above, the longest exposure time your camera can handle should be chosen. Today’s digital cameras can for example go up to 30 seconds whereas smartphones can vary from 2 up to 32 or even 60 seconds exposure. The longer the shutter speed is, the more the sensor will collect light.

Tip: Be careful about the exposure time you choose. There is a limit beyond which the stars get shaped like elongated points, because of the Earth’s rotation about its axis. As we are standing on the Earth, this is not our planet which is moving with respect to us but the sky which rotates with respect to the Earth. While photographing, this rotating motion is noticeable from 20 seconds with a 18 mm standard lens. In order to know what time lapse is the limit before getting star trails, there are some non-intuitive mathematical formulas which work efficiently. However the best way is to check, once you picture is taken, that the stars are not drifting and are round. If not, simply reduce the exposure time from 30 to 20 seconds for example. Stop the process once you found a good middle-ground between have a exposure time long enough and not having star trails.

ISO sensitivity

ISO is what will enable you to bring a gain in brightness on your pictures.  For instance, changing ISO 400 to ISO 1600 will permit to capture fainter details contained in the Milky Way. Do not forget that increasing ISO does not have only advantages. Higher ISO means higher noise, this analog defect produced by the sensor electronics. The image will seem to be less sharp and grainy.
The average value to get enough sensitivity without losing too much quality is around ISO 1600 or ISO 3200.

To summarize the previous paragraphs, here are universal settings which should work in most of the cases for your camera:
– Focal length: 18 mm
– Aperture: F/3.5
– Exposure time: 20 seconds
– ISO Sensitivity: ISO 1600

Focus

Once all the parameters for your image have been correctly selected, one last step still remains to be done: adjusting the focus to avoid blurred stars. It can happen that you do not have the option of manually adjusting your focus on your camera or smartphone. In this case, you should look for a preset “Infinity focus” if available in your camera’s settings.
For classical cameras featuring a focus ring on the lens, it is much easier to find the infinity focus for the stars. Here is the 10-step process:

  1. Install the camera on a tripod or a stand
  2. Choose the focal length of your lens and all the other parameters mentioned above
  3. Activate the Live view mode of your camera (referred to on the screen)
  4. The screen should appear black, that’s normal. However, your camera should be sensitive enough to capture at least one star. Choose a very bright star from the sky (Vega, Altair or Deneb in summer, or Betelgeuse, Sirius or Capella in winter).
  5. Center this star on the screen.
  6. Activate the digital zoom of the Live View (“Magnifying Glass” button) x5 or x10
  7. The star appears magnified on the screen. If you can not see anything even after centering the star, turn the focus ring in one direction and then the other until you see a bright spot on the screen.
  8. To sharpen the focus, turn the focus ring in either direction.
  9. The focus is correct when the bright star has the smallest possible size on the screen (a few pixels)
  10. Disable the Live View and do not touch your lens (zoom) before taking the picture.

Taking the picture

Up to this point, you should have selected the correct parameters of your picture and you have finally found the infinite focus. Congratulations! Now, you just have to press the shutter button of your camera. Using the 5 or 10 seconds timer is a good option to avoid vibration while the camera is taking the picture.
If you are not satisfied of the outcome you get or if you want to improve your Milky Way pictures, find more advice and tips below.

 

Observation conditions

Leave the city

In order get the most light as possible from the Milky Way, it is strongly recommended to drive out of the cities or urban areas where the lights are making your eyes and your camera blind. An entry level camera under a dark sky from the countryside will be more performing than a top-of-the-range camera used in an urban sky.

Avoid the Moonlight

Artificial lights are not the only source of light pollution for astrophotography. The moon is also a real thread for the starry sky because it creates a bright diffuse light in the entire sky. The best conditions for Milky Way photography are between the new moon and the first or last quarter. Otherwise, you should check the moon phases with a dedicated app or website before getting outside and start your shooting session.

Schedule your night

It is also important to have an idea of the current position of the Milky Way in your sky. It is actually not oriented in the same way throughout the year. The best period in the Northern hemisphere is to observe it during summer nights whereas in the Southern hemisphere, it is the opposite.
A quick check on online skymaps or special applications allows you to see the elevation and the elevation of the Milky Way at your current position and time. We can mention apps like: Google Sky Map, Sky Safari, Stellarium Mobile…
Another popular freeware is Stellarium, available on every platform, Windows, Linux and Mac OS.

Image Processing and RAW files

To improve your picture of the Milky Way with an editing software, there is nothing more essential than the format of the picture you selected before capturing it. The high quality “RAW” format (.cr2 , .nef or .dng) enables you to get an uncompressed image while JPEG files will loose more information about the pixels.
Go into your camera settings to enable this RAW pictures option or RAW + JPEG. Then, capture your pictures and import them in your editing software. You can play with the contrast, noise reduction, white colors and more parameters.

Edited Milky Way picture

Photo of the Milky Way before (left) and after processing (right). RAW image of 15 seconds exposure, ISO 3200, 18 mm and f/3.5

Milky Way Stellina

Can we photograph the Milky Way with the Stellina telescope?

Stellina has a 400 mm focal length versus 20 mm focal length for standard wide angle lens for cameras. In other words, its strong magnification will not let you photographing the whole Milky Way. However you, with such a zoom, you will be able to get closer shots of deep sky objects contained inside the Milky Way like nebulae, star clusters, double stars… More details concerning this telescope here.

Red moon Lunar eclipse
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Guide to observe the Total Lunar Eclipse on July 27, 2018

EDIT – Discover the lunar eclipse captured by the Stellina telescope on 07/27/2018 in Martigues, France:
Lunar eclipse 2018

Guide to observe the Total Lunar Eclipse on July 27, 2018

Eclipses are considered as the most fascinating natural phenomena we can observe to the naked eye. On the July 27th 2018, around 9:30 pm (Paris time), the moon will pass accross the Earth’s shadow for about 1 hour and 43 minutes. It makes it the longest total lunar eclipse of the 21st century!

When and how observe it? Why does the moon shift its color to orange-red during an eclipse ? How to photograph it ?
Find out in this article all the information that will help you to better understand this rare phenomenon occuring in the night between July 27th and July 28th in France and Europe.

Total Lunar Eclipse september 28 2015, Credit: Guillaume D.

What is a lunar eclipse?

In Astronomy, we can observe two types of eclipses:

  • A solar eclipse: it occurs when the Sun, the Moon and the Earth are perfectly aligned according to this order. The sun is then more or less covered by the lunar disk. Solar eclipses can be divided into 4 other types, in respect to the alignement of these three bodies: total eclipse, annular eclipse, partial and hybrid. The most astonishing eclipse as we imagine is obviously the total eclipse, when the moon covers entirely the solar disk. Actually, the Earth-Moon distance is 400 times shorter than the Earth-Sun distance but the diameter of the Moon is also 400 times shorter than the sun’s diameter. Thus, the apparent size (apparent diameter) of the Moon is similar or even identical to the apparent size of the Sun as seen from an observer on the ground.
  • A lunar eclipse: it happens when the Moon is not this time located in front of the Earth but behind it. The Moon is then eclipsed by the Earth’s shadow. In contrast to a solar eclipse, an eclipse of the Moon can be easily observed and is harmless for our eyes.

Eclipses, whether they are solar or lunar, occurs at a specific moment of the day. If we look at the Earth-Moon-Sun configuration, we notice that a lunar eclipse will only be visible during the night whereas a solar eclipse can only be spotted at daylight.

Moreover, a lunar eclipse can only happen at a full moon phase because it is when the Sun, the Earth and the Moon are closest to an alignement. However there are not always perfectly aligned otherwise there will be a lunar eclipse every full moon, every month. At least, two is the minimum number of lunar eclipses estimated to occur each year. The total eclipses are the rarest and they do not occur every year.

Position of the Sun, the Earth and the Moon during a total lunar eclipse

Different kinds of Lunar eclipses

Although total eclipses are the most impressive to observe, they are relatively rare. The moon never crosses the shadow of the Earth in the same identical way. In respect to the part of the umbra or penumbra where the moon is shading, we differentiate 3 types of eclipses:

  1. Penumbral lunar eclipses: the moon stays only in the penumbral part of the Earth. These eclipses do not pretend to be entirely interesting since it is difficult to notice a strong difference of brightness in comparison of a traditionnal full moon.
  2. Partial lunar eclipses: a part of the moon is fading in the Earth’s shadow. Visually, this phenomenon produces a side of the moon totally black whereas the other side is still illuminated direcly by the sun. Such an eclipse could be considered as moon phase changing within hours. Except that during an eclipse, the moon is perfectly full.

    Partial lunar eclipse before totality, september 28 2015

  3. Total lunar eclipses: the whole disk of the moon dives in the Earth’s shadow or ‘umbra’. The moon is not completely black but reflect an intense and peculiar orange color, visible to the naked eye. The brightness of the Moon is so low that stars at the background are even visible! You can find an explanation of why the moon has this color below.

The total lunar eclipse of July 27th, step by step

A total eclipse is not instantaneous. In other words, in order the whole surface of the Moon to cross the Earth’s shadow, there must be a series of phases in which the Umbra shades progressively the Moon until it reaches the lowest brightness. These phases or steps are actually corresponding to the 3 types of lunar eclipses already mentionned: the Moon first goes into the penumbral (penumbral eclipse) than shades slowly in the Earth’s shadow (partial eclipse) and finally becomes entirely hidden in the Umbral (total eclipse).

Below are listed the different steps of the total lunar eclipse of July 27th 2018, given in Paris time zone:

The full moon will rise at the East horizon around 9:30 pm. However, the eclipse will have already started two hours prior but the totality phase will begin at the same time the moon will rise.

  • 9:30 pm: Beginning of the total lunar eclipse. The moon appears orange and is very dim. On a normal day, the rising moon is also orange because the atmosphere scatters the colors to keep only the orange one. But here, the moon will also be orange because of the total eclipse.
  • 10:21 pm: Maximum of the total eclipse. It is at this moment that the Moon reaches its minimum brightness in the sky and its strongest coppery hue.
  • 11:13 pm: End of the total eclipse. Beginning of the partial eclipse. The Moon loses its coppery color in order to become gradually white. The Moon is still in the shadow of the Earth but recovers its usual brightness and color.
  • 12:20 pm: End of the partial eclipse. Beginning of the penumbral eclipse. The moon looks like a typical full moon. A photo can help you better notice a possible darker part on the moon.
  • 1:30 am (July 28th, 2018): End of the penumbral eclipse and end of the lunar eclipse. The moon becomes nothing but a simple full moon.

Why is the Moon orange during a total eclipse ?

During an eclipse, we saw that the shadow of our planet is projected onto the surface of the Moon. This shadow would be completely black if the Earth did not have any atmosphere. In fact, the edge of the Earth is marked out by our atmosphere. The light coming from the Sun is absorbed by a thick atmospheric layer composed of particules of air, water and more. Because these particles scatter blue light, they aborb this color from the sunlight to let the others escaping as a filter. The result is that if you remove the blue color, you get a rather orange hue.

Blue and purple strips caused by ozone atmospheric scattering. Credit: Guillaume D.

The Moon gets this tint more or less accentuated according to the thickness and the density of the atmosphere at the moment of the eclipse. Moreover, as the atmopheric layers don’t have the same composition, it is even possible to see other grading colors right before or right after the totality. The image above shows blue and purple strips on one side of the moon caused by the light aborption taking place in the ozone layer.

How to observe and capture the total eclipse ?

A total lunar eclipse can be observed without any protection, since it is simply a full moon plunged into the shadow of the Earth. Consequently, there is no risk to harm our eyes, unlike solar eclipses which require the use of suitable filters.

Thus, a lunar eclipse can be observed with the naked eye, as well as with a pair of binoculars, a refractor or a telescope. There is not a method of observation better than others. For example, looking at the total eclipse with our own eyes lets us see the stars in the background sky as the moon is getting into the shadow. Of course, you will also be able to see the orange color of the moon. In another way, a telescope allows you to admire in detail the surface of the moon entirely tinged with shades of orange and red.

In order to photograph the lunar eclipse, three methods can be adopted according to the equipment you have:

  • If you have a wide angle camera (no zoom), you will not be able to get a close-up view of the moon. However, you will have the opportunity to capture the landscape surrounding the moon: starry sky and landscapes in the foreground. A tripod is highly recommended to stabilize your camera in order to take long exposure pictures.
  • If you have a camera with a zoom lens (200mm, 300mm … etc), you can get amazing close-up views of the moon. You will also need a tripod. The most important thing is to manually choose a short exposure time to avoid having motion blur caused by the motion of the moon and the Earth.
    Typically, an exposure time of less than 2 seconds with a zoom lens of 300 mm should be a good showcase.
  • If you have a telescope –reflector or refractor you can try to photograph the eclipse by sticking your phone’s camera to the eyepiece. This is a technique used by amateur astronomers who want to try astrophotography, but don’t have the appropriate equipment yet. Be careful not to move the telescope while shooting! For the next eclipses, the Stellina telescope will be an ideal solution to capture these moments, thanks to its integrated sensor and automated mode.

You are now ready to attend the total lunar eclipse of July 27th! Feel free to share with us your most beautiful pictures of this event. They might be selected to appear in a special dedicated article on our website.

 

Guillaume Doyen, blogger at Vaonis.com

Asteroid Oumuamua
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OUMUAMUA: Is the first interstellar asteroid finally a comet ?

Discovered on October 17, 2017 , Oumuamua (or 1U/2017 U1) was at the top of the scientific news since it became the first known foreign celestial object coming from another star observed in our solar system. Initially designated as a comet (C/2017 U1), scientists had modified its appellation on October 26th 2017. Since then, it was considered as an asteroid because any coma was detected. However, a recent study has just been published claiming that Oumuamua could be a comet after all!

Particles and jets outgassing

On June 27th 2018, an official paper came out in the world’s famous scientific journal “Nature”, explaining that the asteroid would release tiny amounts of dust and gas, enough to propel and modifying its motion, speed and rotation. Such a phenomenon occurs mostly in comets.

This striking discovery gathering international scientists is the outcome of astronomical observations led with the most powerful telescopes of the world: the Hubble space telescope, the ground-based observatories like Canada-France-Hawaii, Gemini South and the Very Large Telescope (VLT) in Chile.

To get to this conclusion, astronomers tried at first to characterize the asteroid’s trajectory using the celestial mechanics which is affected by the gravitational forces of the Sun and the planets. Stunningly, they noticed that the theoretical position of Oumuamua has an error of 40 000 kilometers and its speed is less than what observations tell.

Through studying in details the evolution of its position, this international team of astronomers whose lead author is Marco Micheli (European Space Agency) could find that something inside the asteroid itself should have sped it up and derived it. Scientists did not expect to this internal force since no trail (coma) was actually observed in the pictures. Even though they are relatively weak, these gas and dust jets would have been released in enough amounts to serve as natural propellant on the asteroid. As a whole, such activity is only observed on comets and with a far more important intensity, which makes it visible through telescopes.

As Oumuamua is currently the first interstellar object of its kind to enter our solar system, to declare whether it is a comet or an asteroid is still a delicate question. The official scientific paper does not end with an unanimous decision, even if it would have comet-like features. Astronomers hope to discover other celestial bodies similar to Oumuamua in order to compare the results and to deduce the exact true nature of this mysterious asteroid.

An Asteroid which has always been keeping astronomers curious

Oumuamua is a fascinating object, which does not unveil all of its secrets. At the moment of its discovery, astronomers had already measured its extremely elongated trajectory, for which any other ones had been observed in the solar system. This characteristic called eccentricity is equal to 1.19, meaning that the motion of Oumuamua is heavily elliptic whereas most of comets or asteroids have an excentricity around 0.2-0.7 whose orbit can be considered as circular. Because of this peculiar orbit, scientists had declared that Oumuamua was likely to come from another planetary system towards the Lyra constellation.

Nuages Noctiluques par Adrien Mauduit
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Noctilucent Clouds : a rare phenomenon happening this summer !

Noctilucent clouds are beyond the shadow of a doubt the rarest and most mysterious we can observe from Earth. They are even less likely to be seen than northern lights ! But, in contrast to aurorae, these night shining clouds can be observed from more countries across Europe !

What is their origin ? How can we observe them ? How to photograph them ? All these answers could be found in this Noctilucent Clouds Guide !

Blue clouds with unusual features

What a overwhelming show observing these clouds, still not very known by the general public today. Displaying a bright blue color and evolving in the dusk sky like waves, the noctilucent clouds show up each year around the summer solstice only. Filaments, undulations, spirals, veils… are the random and unique shapes that they can take.

Noctilucent clouds by Guillaume Doyen

Noctilucent clouds are easily recognizable with their white or bluish undulations. Picture taken by Adrien Mauduit.

When we look at them, it is not surprising to notice that the original English noun “Noctilucent Clouds (NLCs)” means “Night Shining Clouds“. As we will explain it later on, they do not emit any light but do reflect sunlight.

Remark : A lot of synonyms are used to designate these clouds : noctilucent clouds, night shining clouds, polar clouds or mesospheric clouds !

Although they use the word ‘clouds’, NLCs do not have to be misunderstood with common clouds for which we are very familiar with. The famous cumulus, stratus, cumulonimbus, cirrus…etc are part of the atmospheric layer called Troposphere, which rises up to 20 kilometers above sea level. The noctilucent clouds are formed at a specific narrow-range altitude only, which is also far higher : approximately 83 kilometers above the Earth, in the so called mesosphere atmospheric layer, where temperature can reach -100°C.

Moreover, the mesospheric layer is where small meteoroids burnt up in the atmosphere, triggering the phenomenon we all know as shooting stars.

 

Clouds formed by meteors ?

The origin of noctilucent clouds is indeed simultaneously atmospheric and astronomical.
Firstly, every clouds formation requires water molecules floating in the atmosphere. However, at more than 80 kilometers altitude, the temperature is not suitable to form liquid water or water vapor. Therefore, the only presence of water in the mesosphere is ice and comes from the North and South Poles.

In order for these ice crystals to be formed, it is necessary that other matter particles should exist to serve as holders (air, dust…). Shooting stars should be introduced now !

Scientists have recently discovered that ice crystals located in the mesosphere were composed of thin particles released during the ionization of meteors, composing NLCs. The size of these interstellar dusts does not exceed 10 nanometers of diameter, namely 0.000010 millimeters.

These weird clouds are thus extremely thin like smoke produced by cigarettes. One question still worth to be asked : Why can they be visible ?

Why are they visible ?

Photography by Adrien Mauduit

Noctilucent clouds hang at 80 km altitude against 20 km for regular tropospheric clouds. This aerial view was taken by Adrien Mauduit in a plane flying over the polar region.

Only located above the North (or South) pole, noctilucent clouds can be observed by sunlight reflection. For a terrestrial observer, the sun should be setting or rising around the North horizon and stay under the horizon in order for its light to be reflected from under, towards the clouds. At this moment, the common clouds are in shade of the Earth, this is why we can easily distinguish regular clouds to noctilucent clouds which seems to be illuminated.

Typically, the sun must be located at 11° elevation below the horizon. The period of the Year where the Sun shows this particular configuration is around the summer solstice. While in other seasons, the sun is getting much lower under the horizon and not very close to the North horizon.

The sun position is not the only condition which makes the noctilucent clouds observable. The mesosphere is indeed not always cooled down at -100°C. Paradoxically, this extreme temperature is reached only in summer, allowing ice crystals to be formed, and so the NLCs.

How to observe and to photograph Noctilucent Clouds ?

What makes noctilucent clouds mysterious is their unpredictable appearance. Moreover, they can not be seen from anywhere on the Earth, since they form only above the poles (north or south). You should be located next to the polar regions, otherwise the clouds will be too low from horizon or even below it.

As a whole, the latitude of observation of noctilucent clouds varies between 45° (~center of France) and 65° North (~Island). The visibility period spreads from the end of May to the beginning of August, every year.

Location

The more you are located in the North, the higher the probability of observing these spectacular clouds will be. Typically, a location like Normandy (France) or the North of France are particularly interesting. British, Danish, Scandinavian or Canadian people are far more lucky because they have the opportunity to seat at the foreground !

However, previous years have reached records in NLC intensity and observation frequency. For example, they could be observed from lower latitude like French Alps, French Pyrenneans and even Corsica !
Eventually, from anywhere in France or in Europe (latitude higher than 48° North), you should be able to witness at least one display of these beautiful night shining clouds !

Where and When observing ?

Noctilucent clouds occur whether after sunset or before sunrise. Since they are visible thanks to the reflection of sunlight, it is mandatory that the sun, these clouds and the observer should be aligned in this order. This why they always appear above the horizon where the sun set or is about to rise.

Basically, the direction where we should look for them is over the West-North-West horizon (after sunset) or East-North-East (before sunrise). Then, wait at least one hour and a half after sunset before hoping to see NLCs. In the opposite way, if you want to observe them early in the morning, you will have to get up at least one hour and a half before sunrise, this being the upper limit. (two or three hours earlier is safer!)
Of course, NLCs are not visible every single nights ! Do not forget that they are rare.

Photographing Noctilucent Clouds

Given their very low light intensity, it often becomes more beneficial to see these clouds through pictures rather than to the naked eye. It is recommended to use a digital camera (DSLR-like) in order to detect the faintest details. Here is the minimum gear required :

  • A camera featuring a Manual Mode (M Mode)
  • A tripod to stabilize the camera
  • A standard lens (wide angle or zoom)

Before taking pictures, do not forget to adjust the focus manually to infinity.
There are no universal settings to capture NLCs because lighting conditions are always changing according to your location and according to the intensity of these clouds.

To give you some advice in choosing the right settings, we can use few general rules. It is better to increase the ISO sensitivity rather than the exposure time. Indeed, polar clouds are rapidly evolving and a too long integration time will not allow to see the smallest details in their structures.

The picture above is the outcome we can obtain using those settings : 50 mm lens, 6 seconds exposure time, f/2.2 aperture, 400 ISO sensitivity.

Eventually, the most efficient and useful tip to manage your photo is to carry out several series of tests, using different settings.

To close this Noctilucent Clouds guide, there is nothing more mind-blowing than this video recorded by astrophotographer Adrien Mauduit. He is certainly the greatest NLC hunter in the world and collaborated on a project of studying the mesosphere in Canada, involving several future astronauts. The following footage are likely to be the most detailed views of these polar clouds as seen from the ground.

Guillaume Doyen, blogger at Vaonis.com

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Why a Telescope does not need an Eyepiece

Without telescopes, astronomy would not be as popular as today: observing celestial objects through these instruments is a way of being aware of the immensity and the beauty our starry sky features. Astronomical observation enables us to experience directly the marvelous pictures of galaxies, nebulae, star clusters that we see on the Internet or in astronomy books.

But, have you ever looked at the Andromeda Galaxy through the eyepiece of a telescope? Were you surprised to see only a blurred spot, diffuse and without any colors?
It’s a shame, you are told that this object is identical to the Hubble’s picture you found on the Internet!

Today, it is obvious that astronomical observation should be redesigned, modernized and enhanced. Professional astronomers were moreover the first ones to observe the sky using digital images displayed on their computer screens. In a similar way, the French start-up Vaonis offers an original feature which updates stargazing: “photobservation,” which consists of observing objects of our sky with an eyepiece-free telescope equipped with a very high definition camera, sending color images of the object you are looking at in real time to your smartphone or tablet!

If you are among those who are not convinced that the future of astronomical observation is in the replacement of telescope eyepieces by high-performance cameras transferring data directly to our connected devices, you should keep reading this article. It might change your point of view.

Observation through an eyepiece: the biggest disappointment of astronomy!

Contrary to the expectations of most people, looking through a telescope’s eyepiece does not mean observing images as sharp, as bright and as colorful as the ones we often see on Internet or in scientific magazines.

The overall image quality does not depend solely on the optical quality of the telescope, but rather on the capabilities of our eyes. Although our eyes are extremely powerful tools that no camera could match, when night falls, that is no longer the case!

The weaknesses of the human eye in astronomy: anatomy reminder

First of all, our eyes require a minimum amount of time to adjust to darkness. Between 10 and 15 minutes are needed in order to detect the slight contrast of a nebula or galaxy through a telescope or even of the Milky Way observed by the naked eye.
Obviously, our eye sensitivity is limited and does not permit us to observe objects of the starry sky at their best.

Composition of human eye

The human eye contains two kinds of photodetectors which are spread out on the surface of the retina: cones and rods. These photo-receivers are responsible for our sight and our ability to detect different colors. Cones are sensitive to colors and are divided into 3 types: red, green and blue. They are constantly used for our daylight vision, but when the luminosity plummets, the rods take their place. Rods are far more numerous than the cones but are insensitive to color!

On one hand, it is thanks to the rods that we have night vision at all, and on the other hand, it is because of them that our night vision is only in shades of black and white!

As a consequence, we will never be able to observing the colors of galaxies and nebulae without a huge amount of light to make their shapes and borders stand out. This applies both to telescope eyepiece observation and to naked eye observation.

The drawbacks of classical observation: one observer at a time

Even without taking into account the physical limits of our eyes, telescope observation has not always been as simple as one might think. Here is a list of difficulties encountered when observing through the eyepiece of a telescope:

  • Lonely observation because only one person at a time can observe through the instrument
  • The eye should not touch the eyepiece in order to keep the telescope stable
  • The focus is different for every observer, and the telescope shakes while adjusting it
  • The observation position is often uncomfortable: you must bend, crouch or even climb up to reach the eyepiece!

A screen: observing + photographing = “photobserving”

Orion nebula visual observing vs photographyImage comparison between of the Orion Nebula as seen with the eye through the eyepiece of a telescope (left, simulation) and an image obtained with a telescope with an embedded camera like Stellina (right)

In the end, eyepiece observation is not the best way to appreciate the beauties of the universe. In addition to being uncomfortable, traditional observation is limited by the capacity of our eyes to differentiate among the low luminosity stars and other celestial objects.

The primary purpose of astronomical observation is to observe objects of the sky with the highest quality possible. Since modifying the human eye remains impossible, the typical solution for improvement is to purchase bigger telescopes, which leads to spending more money. Even with larger telescopes, the result sill does not match our expectations.

Given this frustrating limiting factor of our eyes, a question can arises: since nowadays we have technology powerful enough to exceed the performance of our eyes at the night, wouldn’t it make more sense to remove the eyepiece and instead embed a CCD sensor?

Observing the colors of the Universe, at last!

Indeed, not only does a photo sensor reveal the true colors of nebulae and galaxies but also enables us to detect objects which were totally invisible through a telescope eyepiece!

The list of accessible sky objects thus becomes richer and the satisfaction of these images is even greater, because they reveal much more detail.

Real-time images on your smartphone

No need to adjust your night vision and to try to guess which astronomical object you are looking at. The captured photograph is directly shown on your tablet’s or smartphone’s screen, through WiFi.

Importantly, a Stellina telescope does not simply display an instantaneous grayish view of an object;  rather, it uses the process of live-Stacking, which consists basically of taking a series of pictures and superimposing them one by one. This technical process derives from practices by professional astronomers, and enables Stellina to make the celestial body stand out while the clock is ticking, by light amplification. The longer you keep the telescope pointed at an object, the brighter and the more visible it will be.

The mobile app provided with Stellina performs the entire image processing and automatically chooses the suitable image processing for each object. This permits you to avoid the complicated and unintuitive field of astronomical image processing.

A screen for sharing your experience and having a collective observation

Using the screen of a smartphone to replace the telescope eyepiece is especially appreciated when you wish to move freely about your telescope without having to come back and forth to it every minute. With this system, it is now possible to invite family or friends to observe your images simultaneously keeping your seat on your patio or even in your living room!
Your tablet serves as a support to look at your pictures and also as an interactive link to share your experience on every social network.

Sharing your astrophotographical work will never be as simple and effective as with Stellina. Stellina allows each of us to SHARE OUR UNIVERSE!

Why a telescopes does not need an eyeiece

New future for astronomy

Thanks to an eyepiece-free telescope, you will never need to fuss with focusing the telescope, changing the eyepiece, etc. The telescope will be ready to use within a few seconds.

A telescope like Stellina can help you observe the beauty of our universe at it’s best, and even make your first steps in advanced astronomy: collaborative astronomy. Asteroid occultations with 3D rendering, variable stars monitoring, exoplanet transits wich were previously limited to professional astronomers will now all be accessible to everyone.

Select the Universe which suits you the best with a new generation telescope: Stellina.

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How an embedded telescope heater improves your images

The beautiful summer nights are upcoming and so the best period of the year to set your telescope up and making your first steps in astrophotography ! However, what is it more frustrating than realizing that all of your pictures got blurred because of condensation while your telescope setup was running?

How to cope with condensation, these so called water droplets which shortcut your astronomical observations ? Choosing a telescope with an integrated heater, or add a heater to your instrument is the best way to get rid of it. This resistor produces heat around the telescope optics and decreases the humidity level, stopping  the formation of dew.

Among all the telescopes we can find on the mass market, Stellina telescope is the only one which offers this feature. Equipped with temperature and humidity sensors, it automatically detects when the condensation is about to be formed.

Where does the dew come from ?

It happens very often to have condensation while observing the night sky, except in a very dry place with a low humidity (desert…).

In the night, the temperature variations are far more accentuated than the day. A starry sky without any cloud coverage lets the warm air leaving away, thus, decreasing the temperature. Added to this brutal cooling, the wet ground often releases the heat it has collected all day long.

All these annoying weather conditions give rise to the condensation (or dew) since they make the dew point getting closer to the ambient temperature. Basically, this particular point corresponds to the temperature threshold over which the condensation will never form. Unfortunately, if your telescope cools down to a temperature below the dew point, the condensation will appear.The chart above shows the relation of the dew point to the humidity rate and the ambient temperature (outside). The colder and the wetter the nights are, the closer to the ambient temperature the dew point is. This amounts to saying that the condensation will appear easily on your telescope within few minutes.

What is the effect of dew in Astronomy ?

Condensation is what the amateur astronomers are afraid of. When these water droplets stick to the lens or the mirror of your telescope, they have similar effect as filters and damage drastically the image quality. Not only the details decrease but also the amount of collected light.

In astrophotography, the image of a celestial object you would get would seem dark and blurred. The same result you have when you do not correctly focus your camera.

Comparison of two pictures of the Orion Nebula. The left one  is a simulated picture showing the impact of dew on the image, whereas the right picture shows a picture taken in optimal conditions.

The ageing of the electronic, mechanical and optical components of your telescope is also accelerated by condensation.

How to cope with it ?

The dew is nothing but natural. Thus, every telescope you could find on the market will undergo the condensation. The only solution is to use a system capable of warming up the optics just to a temperature over the dew point. Indeed, this simple temperature elevation is sufficient enough to keep the instrument out of risks.

A anti-condensation heater is the amateur astronomers’ best friend. Say goodbye to your astronomical observations disturbed and shortcut by humidity stuck on your telescope !

Stellina integrates a dew control system, fully integrated and adapting to its environment automatically. . At Vaonis, we got the feedback from astrophotographers, their success stories, their biggest worries while capturing the night sky and their expectations. For now, Stellina telescope is the unique telescope in the mass market to offer an integrated heater.

Stellina’s dew control system : more than a simple heater !

For an optimal protection against dew, Vaonis did not chose to use a single resistor but ten heating resistors equally spaced around the front lens of Stellina. You probably already know that similarly to our toaster or electric heating, condensation heaters are big power consumers ! This is absolutely not an issue with Stellina since the system switches on only when it finds that the telescope must be warmed up, and optimize its energy consumption. Embedded temperature and humidity sensors inform the telescope in real time whether the condensation is likely to appear or not.

We also take care about the users who would like to control the heater by themselves. Therefore, we added a manual mode, so this will insure the deep sky photographs to be entirely condensation-free.

 

Astrophotography has never been so intuitive and relaxed than with Stellina.