You are looking at the starry sky from a planet that orbits around the sun at about 30 km per second. In addition, the Earth rotates on itself, making a complete rotation every 23 hours, 56 minutes and 4 seconds.
Therefore, depending on your location and the date and time of your observation, visible stars and constellations are not always the same. Their positions even keep changing during your observation.
In these circumstances, accurately pointing to a star (often invisible to the naked eye) with a telescope and following its movement to capture sharp images is a real technical challenge. A telescope must be set up in a rigorous and precise manner, taking into account the date and location information.
This time-lapse video shows the apparent movement of the stars caused by the Earth’s rotation. The position of the stars is permanently changing.
With a classical telescope, the setting-up procedure required to be fully operational and start capturing images of celestial objects can take between 30 minutes and 1 hour, even for an experienced amateur astronomer. With Stellina or Vespera, on the other hand, it only takes a few minutes and no particular technical skill.
Here is a detailed description of the setting-up and initialization process of the Vaonis observing stations and an explanation of why the process is easier and faster than with a conventional telescope.
1. Requirements for a successful initialization
1.1 External conditions
Apart from solar observations which require appropriate filters, initialization of the two telescopes for night observation requires a dark enough sky and visible stars. It is not necessary to wait for complete darkness. The observation stations can initialize from the nautical twilight when the sun goes down 6° below the horizon. However, the initialization duration of Stellina and Vespera can be shorter if it is a very dark night.
The sky must also be clear enough. In case of heavy cloud cover, initialization may fail. In any event, under these conditions, most observations are impossible.
1.2 Leveling the tripod
A similar step in setting-up Stellina and Vespera with a classic telescope is that it is required that the tripod be set horizontally. It is done manually by adjusting the length of each leg and checking the spirit level so that the bubble is positioned precisely in the center of the black circle.
Tip: Look at the spirit level from above to be sure of the position of the bubble. If you look at it from a different angle, you may think it is well centered while it’s actually not (due to the parallax).
2. What is the initialization of a telescope?
2.1 Why is initialization necessary?
The start-up of Stellina and Vespera is much quicker than that of a classical telescope: less than 5 minutes in good conditions versus more than 1 hour for classical equipment. The main reason is that they are fewer manipulations to perform. Above all, one particularly long and complex step of the process with a classical telescope that is fully automatic with Stellina and Vespera is the syncing with the celestial sphere.
As explained previously, the appearance of the sky is constantly changing. Using a telescope to capture images of the universe requires accurate synchronization with the orientation and rotation of the sky. Time and geographical location must be taken into account. The mount axis must also be aligned in a particular way. Then the telescope can calculate the stars’ position and activate its motors to point and follow the lead to observe.
2.2 Stellina / Vespera: automatic initialization with astrometric calibration
Step 1: Geolocation and time syncing
Firstly, to properly operate, the observation stations must be input with the time and the geographical position. This information is retrieved from the connected device you use to control the telescopes.
If Stellinapp indicates it can’t get the geographical coordinates of your observation place, your smartphone or tablet may not have an integrated GPS, or it could be disabled. You can input your geographical coordinates (longitude and latitude) manually if necessary.
Step 2: Astrometric calibration
Stellina and Vespera have to determine their orientation with respect to the starry sky position and the horizontal (although the horizontal alignment has been achieved manually with the spirit level, it may be necessary to improve it for further accuracy).
To achieve this, our stations use the astrometric calibration method, also known as “plate-solving” calibration. It consists of comparing the starfield captured by the telescope with an internal database to identify the targeted region of the sky:
- The observation station targets a random area of the sky.
- It captures an image of the bright stars.
- The onboard computer analyzes the resulting image to determine patterns formed by groups of stars.
- The patterns are compared with an internal database to find a match and determine the sky target region.
In case of a fail, the observing station starts over with another region of the sky. Most of the time, the second attempt is successful. Clouds or haze in the targeted region of the sky may be responsible for the failure.
Step 3: Tracking activation
To remain in sync with the sky, Stellina and Vespera must follow the apparent movement of the stars caused by the rotation of Earth. This is accomplished by continuously activating the motors on the two axes of the telescope (and a third axis on Stellina which also compensates the starfield rotation).
Step 4: Focusing
Focusing consists of adjusting the sharpness of the image generated by the telescope. It is achieved by adjusting the distance between the lens and the camera in order to view the stars as sharply as possible.
Successful focus allows one to get the maximum amount of detail on the images of galaxies and nebulae.
Stellina and Vespera have an integrated automatic focuser. To this day, it is the only astronomy consumer telescope in the world equipped with such a feature.
With conventional telescopes, focusing is done manually using various methods, such as using Bathinov or Hartman masks or checking star diffraction spikes, possibly with specific astronomy software. The observer is the final judge of the sharpness of the images (focus).
2.3 Classical telescope: polar alignment
Classical telescopes are often equipped with an equatorial mount (while Stellina and Vespera have an azimuthal mount). It facilitates star tracking, yet above all, it is required to capture images of the universe. When properly installed, the equatorial mount allows one to follow the apparent rotation of the sky by performing a slow and steady course on one of its axes. It is also required to keep the object’s orientation in the field of view (essential for astrophotography). Stellina and Vespera have a mechanism to compensate for the field rotation (optical for Stellina and software-based for Vespera) to get the same result as an equatorial mount.
To achieve the polar alignment, the observer must sequentially point to different stars. Depending on the accuracy of the result, he must manually apply corrections to the orientation of the polar mount axis.
Some mounts are equipped with a viewfinder built into the polar axis, allowing for a first approximate orientation by targeting the North Star.
On conventional telescopes, astrometric calibration does not apply as they do not have an integrated camera and an onboard computer system to operate.
3. Six tips to reduce initialization time or limit failure?
- Regularly check to ensure that your Stellinapp mobile application and the internal program of the telescope are up to date. Visit the App Store or Google Play Store to check if new versions are available. You can subscribe to the Vaonis newsletter to be notified of updates and new features.
- Set up the telescope’s tripod on a flat, stable, and non-slippery surface (avoid loose soil or sand). If the mount moves during your observation, the calibration will lose its effectiveness.
- Shelter the telescope from the wind.
- Level the tripod as carefully as possible with the spirit level.
- Wait for sufficient darkness before starting the initialization.
- Before starting the initialization of Stellina or Vespera, rotate the telescope’s body on its tripod (taking care not to move the tripod) towards a region of the sky free of obstructions, clouds, and stray light sources such as street lamps. The stars should be clearly visible in the chosen area.
During the observation, if you find that your telescope struggles to point to a new object accurately or that stars are oval-shaped rather than circular, you can solve the issue by restarting the initialization.