Occultations of stars by asteroids

In astronomy, an occultation occurs when something between you and a distant object blocks your view of that distant objectA star is occulted by an asteroid when the asteroid passes inbetween the observer and the star during its movement around the Sun. This occults the star from the observer’s point of view, and instead of the light from the star and the asteroid we observe only the light coming from the asteroid. As most of the asteroids are smaller and dimly luminous bodies, there is usually a significant decrease in brightness during the occultation. When looking at the Earth from space, the asteroid actually casts its shadow on the Earth’s surface. Since we know exactly the speed of the asteroid’s motion, we can deduce the asteroid’s size from the length of the decrease in the brightness of the star. If the observations from several observers at different locations on the Earth’s surface are combined, we can even determine the profile of the asteroid, i.e. its shape when it is currently turned towards the Earth, because asteroids are usually not spherical, but rather irregular in shape.


We have been observing since September 2014 with the new Planewave CDK17 telescope, which is located in the southeast dome on the new 2EL DDF2-EQ-600 fork mount. Thanks to this, the possibility of observing star occultations by asteroids and other phenomena has been significantly improved, especially thanks to the diameter of the main mirror of 43 cm and a high-quality optical system of the modified Dall-Kirkham type. Compared to the past, it allows us to observe the occultations of much fainter stars, and the accuracy of the measurements has also increased significantly. At an aperture of f/6.8, the telescope has a focal length of 2939 mm, which is usually shortened to 1980 mm with a 0.66× focus reducer, thus achieving an aperture of f/4.6.

We use a Kepler FL4040 CMOS camera for observation. The camera has an effective area of 4048×4048 pixels. The camera has a built-in GPS module, so it allows to record the exact time when the picture was taken. Furthermore, it is able to take pictures in continuous mode, where there is no gap between individual pictures and the recording is therefore similar to if it were a video camera.


Observation results

We will add our results to this section in near future, our website is still undergoin reconstruction.