Observation of stars during the day or day astronomy

Due to the fact that our previous article on “ How different cameras and devices are seen at night ” aroused great interest among readers, we decided to acquaint you with another highly specialized area of ​​application for video cameras, such as day astronomy. To many, the task of observing the stars during the day may be a waste of time, but we will try to convince you at the end of the article.

Attention! Further in the article there will be quite large gif-animations of 4-8MB!

“All video and photo materials of this article are unique for Runet and belong to the organizations that provided them. When reprinting, reference to this article is obligatory. ”

These are not stars, but it looks funny and accidentally filmed on the camera, which we are talking about in the article =)


Unfortunately, we live in such a strange place that during the whole autumn and winter we had about 20 hours of clear skies and in most cases these hours were in the daytime. Therefore, shooting the stars during the day is at least a small opportunity to quench your thirst for astronomy.

Two unique cameras that could potentially see stars by day fell into our hands. Cameras work in different ranges. One camera: VC1300HDR is a black and white camera of the visible range, the second VSM320 is a near-IR camera (0.9-1.8 micron). Both cameras are designed and manufactured in Russia, the processing algorithms, despite their apparent simplicity, are the intellectual property of device manufacturers.

We will try to clarify in general terms, which limits the ability of a video camera to detect a star during the day - this is, of course, a huge background illumination of the sky, which the closer to the Sun - the greater. When you try to shoot the sky directly, the exposure of each individual frame is so short that the signal from the star is very weak. Thus, the bright background of the sky is the main limitation when shooting. What are the ways to reduce sky background? Oddly enough, you need to reduce the aperture of the lens. With a constant aperture (the diameter of the mirror or the front lens) a decrease in luminosity is achieved by increasing the focal length.

This is a limitation on the part of the physics of the process: it is desirable to reduce the field of view.

What limits the possibility of observation from the side of technology? The main thing that limits the video camera in its detecting ability is the capacity in electrons of the photosensitive element. If the capacity is small, you are forced to reduce the exposure so as not to get a white frame without information. The shorter the exposure, the less information you get when observing, the lower the signal-to-noise ratio.

Thus, the limitation from the side of technology is the pixel capacity of the camera.

Where does the noise come from? After all, it seems that you can take the best low-noise camera, take a piece of the sky and then carefully process the brightness level, and where the brightness level exceeds the average level, will there be a star? But it is not. The noise due to the quantum nature of light is called photon noise and is described by the Poisson distribution, the most important property of which is the dispersion value of the received signal, which is equal to the root of the accumulated charge. Thus, if you have accumulated 10,000 electrons in the cell, then the photon noise will be the root of this value or 100e, and the signal-to-noise ratio will be 100. For a pixel capacity of 1,000,000e, the photon noise will be 1000e, and the signal / noise (as the level of the maximum possible accumulated signal to photon noise) is also 1000. As the pixel capacity increases, the achievable signal-to-noise ratio increases. In order to detect a star, it is necessary to accumulate the amount of signal, in general, exceeding the photon noise level. As was shown above, with an increase in the accumulation time a hundred times, the photon noise only grows 10 times, and the signal from the star will grow almost proportionally, that is, also 100 times.

The main conclusion of this reasoning is that the capacity of the photosensitive element is of crucial importance. In most cases, the capacity of photocells of household cameras does not exceed 20,000e, and the cameras for scientific use are 100,000e.

The capacity of the photo element of the camera VC1300HDR declared in 2.4 million electrons.
The photo capacity of the VS320 camera element is about 3.5 million electrons.
Large capacity makes these cameras potentially suitable for daytime astronomy.

Since the dear reader has already waited for pictures, then the text will be smaller.

Camera of visible range , resolution: 640x512, Newton telescope 200mm, without light filters, all processing is done inside the camera. Shooting conditions: February 8, 2018, latitude 58'31 ', longitude 31'16, time from 10.30 to 12 days, all shooting was done in video mode at 25Hz.


Alpha Perseus (Mirfak), stars in = 1.8m., The shooting time T = 11: 34


Gamma Perseus, 3.0m, T = 11: 34


Perseus Delta, 2.9m, T = 10: 38


Psi Perseus, 4.3m, T = 10: 38

For those who want to watch the original video (without bills, compression and SMS)), links: one and two . Well, the weather report at the time of shooting ...





Photo camera on the telescope. Let the real astronomers scold us, but it was very cold, so they shot right from the balcony, without even opening the window ... Brrrr ...)

Near-infrared camera , VSM320, resolution 320x256, Newton telescope with corrector A = 114mm, F = 1000mm, without light filters, all processing is done inside the camera. Shooting conditions: January 16, 2018, latitude 58'31 ', longitude 31'16, time from 14.00 to 16 days, all shooting was done in video mode at a frequency of 25 Hz.


SAO75151 (Hamal Alpha Aries), 2m, T = 14: 11. Video


SAO55306, 3m, T = 14: 42. Video


SAO38559 and SAO38551, 6m and 6.9m, T = 15: 32. Video


SAO38890, SAO38937, SAO38917; 4.35m, 6.6m, 5.45m (blue star class), T = 16: 03. Video

Well, the weather report at the time of shooting ...



Thus, it can be noted that the presented cameras really cope with the task of detecting stars during the day and allow us to make daytime astronomical observations even in high light conditions. It should be noted that the near-infrared camera, despite the lower resolution and slightly larger photocell capacity, has a significantly better detecting ability, although it is better for orange and red objects.

Now you can ask: why this may be needed?

Well, first, if necessary, you can work during the day on the stars or other space objects and provide them with support. And secondly, the opportunity to work on atmospheric objects during the day.

Here are some unique examples of optical location, taken on a VC1300 camera, field of view 12x10 degrees, frame rate 25Hz (materials from the archive of 2014).


Optical location, mainline aircraft at a distance of more than 100km (frequency reduced, the original frequency of 25 Hz). Black dots are birds. Full video link .

Here is the Flightradar data:



And the distance by Yandex:



It should be noted: in spite of the fact that the main planes seem large, the diameter of the fuselage does not exceed 4 meters. What at a distance of 100km gives an image of an airplane much smaller than a pixel (for a fairly wide viewing angle, as in the video).

Well, a small bonus for those who read the article to the end =) another remarkable example of optical location, already by birds (frame rate lowered):


→ Link to video

And it is also a flock of birds:



We hope that this article was useful and was able to visually show the features and difficulties faced by daytime astronomy, and also we were able to demonstrate the use of unique video tools for optical location tasks.

I want to express my gratitude to the colleagues who helped to collect, capture and process the material, as well as to the organizations that provided the cameras, archival materials and permission to publish.

When using these materials reference to this article is required.