What is it ?

It is an astronomical event defined by the passage of an object in front of a star.
The star is completely or partially obscured. Here we will be interested by asteroid occultation. For example, see the next GIF.

Why observe them ?

Asteroids were unknown until 1801, with the discovery of the largest asteroid one : 1 Ceres, which reaches 930km in diameter ! The current scientific consensus states that Main-Belt asteroids between Mars and Jupiter were supposed to turn into a planet during the creation of our solar system.

Due to the huge gravity of Jupiter, this Main-Belt remained as it is, a collection of objects and not a single body. Therefore, we can say that these asteroids are witnesses to the creation of our solar system and our planet. By studying them more closely, we can learn about their trajectory and identify their shape, their size, their composition etc. And possibly learn about the origin of life. Observing asteroid occultation is about observing an asteroid passing between a bright star and us.

HowTo guide

First, go to our occultation prediction page and select the occultation you want to do.

To find out if an occultation is passing through your home, simply zoom by scrolling on the map. If you live between the two orange lines, you are able to see the occultation.

For your information :

CEST/CET time* is the Central Europe Summer Time. It concerned France, Spain, Italy, Germany, Switzerland etc…

BST/GMT time* concerned only Portugal and United Kingdom

EEST/EET time* concerned only Finland

Check this complete User Manual Link on how to catch one with your Unistellar eVscope.

Before the occultation :

✔️ Check the weather 

We suggest you use the clearoutside app or website.

(see p.5 in theUser Manual link)

✔️ Clear the memory of your eVscope

WARNING : this step can take up to 30 minutes – 2 hours depending on your Internet connection.

(see p.9 in theUser Manual link)

✔️ Charge the battery of your eVscope

✔️ Look for updates the Unistellar application (Apple and Android stores).

30 min before the occultation begins:

✔️ Set up your eVscope and level the tripod 

Make sure you find have a good view on the constellation of the event

(see p.13 in theUser Manual link)

✔️Launch the Unistellar application

Make sure that your smartphone is connected to your 4G/Wi-Fi BEFORE launching the application. Then, launch first the app WITHOUT launching your eVscope. 

✔️Turn your eVscope on

You can connect your phone to your eVscope now. 

✔️ Launch Autonomous Field Detection

So that your eVscope knows precisely how to go to the occulted star.

(see p.17 in theUser Manual link)

✔️ Focus and collimation

By pointing one of the first stars recommended by the app and using the Bahtinov Mask.

(see p.18 in theUser Manual link)

15 minutes before the occultation:

In the “Target” field enter the RA/DEC parameters and press GOTO before the beginning of the occultation. In the “recording” tab enter the Gain, Exposure and Duration parameters, check again your values and click on “Launch” at the start time.


Remark : Once the recording has started, you can now switch back to the eVscope page to try and see the occultation in real time. Please note that this is a really difficult event to observe directly. 

Do not activate the enhanced Vision during recording : it would delete all the data.


🏡 Once at home :

✔️Transfer your data 

Once recording is over, please transfer your data. (If you need help please check: HowTo upload my data ? )

✔Tell Unistellar that you participated

To make sure your contribution is properly processed, please fill THIS REPORT.

⚠️ Please, fill this survey, we can only process data registered that way ⚠️

🥂 Congratulations ! 🥂

You have achieved your citizen science mission. Unistellar and SETI Institute scientists thank you and hope you enjoyed it.

We will publish the occultation results soon on EURASTER.

It is a small step for you, and a big step for citizen science.

"What a Feeling:" A Testimonial from an Occultation's Detector

Here is what Morand, one of Unistellar’s first citizen astronomers, wrote about his detection of asteroid 2000 UD52:

When I received this occultation “mission”, I was a little confused. It seemed quite simple, the event was known, so no chance discovery by amateurs … But hey, I played the game. I had just received the telescope.

Excited but a little late as always, I followed the procedure and … I saw nothing … However, I sent the data. And, a few days later, I learned that the occultation was clearly visible on the data, that I was the only Unistellar to have observed it, and that the scientific value was real : the occultation was very brief, 0.3s (the predicted maximum was 0.8s), therefore particularly difficult considering the small size of the asteroid (~ 6.6 km) and the width of its centrality band.

Having observers near and into the centrality band will allow to better determine the position of the asteroid, and therefore to refine its orbit ! What a feeling !