Author: Guillaume Doyen

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
Tips & News

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.


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

Tips & News

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.


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TESS : a chance of discovering a new Earth within 2 years !

What if the next life-hosting and Earth-like planet would be discovered within the upcoming 2 years ?

Although the answer is not as obvious as we could imagine, it remains not impossible either, thanks to the very recent launch of the space mission TESS by NASA.

The exoplanet hunting has never been at the heart of our preoccupation as today !

How did exoplanets survey begin ?

Since the discovery of the first exoplanet in 1992 (named Poltergeist and orbiting around a Pulsar), mankind just became aware that the Universe, despite its immensity, could hide other planets, other solar systems and even potentially other Earths, where proliferation of life could be possible.

Before the birth of space telescopes, these planets orbiting foreign stars located inside our Galaxy were mainly discovered in few quantity, using ground-based telescopes only.

We had to wait the 2000s for the famous Hubble Space Telescope to be used for the first time as a tool looking for exoplanets. Its primary task was about to confirm the presence of exoplanet which had been previously discovered. Later on March 22, 2005 NASA announced that its Spitzer telescope performed the first direct exoplanet observation ever. Nonetheless, the performances and availability of the Hubble and the Spitzer telescopes do not make them suitable enough to reach high-expected results needed for this kind of research.

NASA therefore decided to launch a space mission entirely dedicated for exoplanets hunting : Kepler.

The desire to go further

If the number of discovered exoplanets as of May 2018 reached 3767, it is mainly thanks to Kepler mission which counts 2512 confirmed exoplanets for itself. Definitely the biggest amount of exoplanets for a single mission.

After 9 years of commission, the Kepler’s end of mission is coming and it is currently transmitting its last data before NASA will decide to shut it down forever. However, one the main drawbacks remains its narrow area of monitoring, which was not as wide as what the next generation TESS will perform.
It is time now to dive in depth into TESS scientific and technical details.

TESS : a prolific mission ahead

The Transiting Exoplanet Survey Satellite (or TESS) was launched on April 18, 2018 by a SpaceX Falcon 9 rocket.
TESS is not a single space telescope but actually a 4-wide-view-telescope-embedded satelliteDuring its mission estimated to last two years, scientists want to monitor more than 200 000 bright stars and detect potential change of luminosity caused by an exoplanet crossing the disk of its host star. This detection method of exoplanets is a so-called “transiting method”.

So, the ambition of TESS is to unveil at least 20 000 exoplanets whose 5 % of them would be similar to the Earth, in term of size.

 This ambition would be never fulfilled without scanning the whole starry sky. One of the main features of this space telescope is indeed the ability to use four great-aperture telescopes (f/1.4), covering a wide zone of 24×24 degrees each. Consequently, the total zone used by TESS is 400 times bigger than the one used by the Kepler telescope !

How does TESS detect exoplanets ?

Nearly the whole sky will be observed and divided into North-South hemispheres which count 13 zones each. TESS will perform a single zone monitoring within 4 weeks. It amounts to saying that the 26 zones will be entirely monitored after 2 years.

The orbit where the telescope has been moved on is strongly elliptical, with a 14 days period. Every nearest approach of the Earth, TESS will transmit systematically the data acquired during its 2-week-long measurements. As a matter of fact, these data are mostly images taken by the four CCD sensors of 16.8 Mega pixels each. They are extremely relevant because they contain all the photometric properties of the stars, namely their light variation throughout the time.

From these measurements, not only the size of the exoplanets could be deduced but also the orbital parameters such as their orbital period, distance from their host star… An estimation of their mass could only be done by the biggest ground-based observatories.

Catching some exoplanets using your own telescope is not science-fiction !

Tough, observing exoplanets is not only limited to scientific and professional research. Using less top-of-the-range telescopes, affordable to amateurs, it is actually possible to detect some exoplanets with the transiting method like TESS. A telescope which features a 400 mm minimum focal length, a diameter from 80 mm and a camera – the same specs as the Stellina telescope for example) allow you to make your first lights in exoplanet hunting.

As you might probably guess, TESS is bound to obtain more sensitive light curves and has a far higher efficiency. Its scientific mission is expected to start on mid-June, few times after it will reach its work-orbit.

Guillaume Doyen