Video astronomy: an update

Early last year I posted an article discussing the merits of webcam imaging. I had just bought some new equipment and wanted to put my enthusiasm into blog form. I was getting fed up with the annoying short observing time our cloudy nights provide us in the UK. Traditional long exposure photography, used to capture faint galaxies and nebulae, is simply out of the question on all but the clearest of nights. However, webcam astronomy is easy to learn, cheap and quick enough to do between clouds. Not only this but, on Moonlit nights when long exposure photography would produce washed out pictures of galaxies, webcam imaging can deliver great Lunar landscapes. Also, during the day, a webcam coupled with a telescope can capture the ever-changing surface of the Sun, meaning you can do astronomy without losing sleep!

So it is now time to show you some of my attempts at webcam astronomy. Before I show any processed images I first want to demonstrate the main limitation facing astrophotography (other than light pollution); atmospheric turbulence. In image 1, a section of the Moon is being videoed; notice how the detail is constantly shifting in and out of focus. This distortion is caused by currents of air at different temperatures which bend and scatter the light passing through the atmosphere.

Image 1. A movie clip of craters Aristoteles (top left) and Eudoxus (top right). The image shimmers because of the constant turbulence in Earth’s atmosphere. Author’s own work.

Although this may look bad, atmospheric distortion can get far worse! For instance, if the Moon moves close to the horizon then light coming from its surface has to travel through far more air, which badly distorts and scatters this light. Just look at how distorted the Sun looks as it is setting. Atmospheric distortion can also be caused in other ways. In image 2, the Moon was passing just above my house, which unfortunately is not well insulated. This atmospheric distortion caused by hot air escaping from my house dramatically reduces the detail you can see – I’d ask my wife to keep the heating off while I’m imaging but I fear this wouldn’t go down too well.

Image 2. Another movie clip taken when the Moon was setting just above my house. The hot air causes increased turbulence that causes the detail of the lunar landscape to dance and blur. Author’s own work.

Luckily webcam astronomy possesses one amazing advantage over other forms of photography. Unlike traditional long exposure astrophotography, video recordings produces thousands of individual images (or frames) of your target, this means you can be very strict about which frames to keep and which to discard. For example, to get one high quality image, I take about 4 minutes of video containing 14400 frames at 60 frames/sec. I then pick the best 2000 of these frames and, using a program called Pipp, I can stack them together to reduce noise and improve detail (see previous post about stacking). This procedure means I can remove all the frames that were distorted by the atmosphere.

So after all that processing what am I left with? The answer is superior detail, better than any individual frame in the movie or even images taken using long exposure photography. In Image 3, Lunar detail as small as 1Km across can be seen, since the Moon was 370000Km away at that point, this resolution is equivalent to spotting a 2cm wide 1p coin from 7.4Km away! Quite an achievement for my small telescope. All because I have used only the frames taken during atmospheric stillness.

Image 3. A stacked image taken using the best 2000 frames of the movie (Figure 1). The resolution has now improved substantially. Author’s own work.

Even during strong atmospheric turbulence, reasonable detail can be retrieved, in Image 4, Lunar craters as small as about 5 Km can be seen, not as good as in Image 3 but still impressive.

Image 4. The stacked image from the movie shown in Image 2. Despite the strong atmospheric disturbance, fine detail can still be resolved. The crater to the far left is Sacrobosco. Author’s own work.

Of course webcam astronomy is not limited to the Moon. With the correct light rejecting filters, you can turn this powerful technique onto the Sun. During July 2016 there was a fantastic chain of Sunspots (see Image 5), these features change shape every day: merging, splitting and distorting providing a very dynamic and unique astronomical sight.
Of course before undertaking solar photography a few considerations must be addressed. (1) Make sure you research how to observe/image the Sun safely, I will not be happy if you go out and blind yourself after reading this article. (2) Be aware that the Sun will heat up your telescope creating turbulent air inside the tube, to avoid this problem I covered my scope in kitchen foil.

Image 5. A stacked image of sunspots taken on 19/07/2016. The internal structure of the Sunspots can be seen as well as individual granulations across the solar surface. Author’s own work.

The planets are probably the most popular and evocative telescopic targets of all. Thankfully webcam imaging provides an easy way to image them and make your own Solar system collections! I’ve added my own incomplete collection in Figure 6. The sizes the planets appear are to scale.

Image 6. My Solar System collection: Jupiter (top left), Uranus (top middle), Neptune (top right), Mars (bottom left) and Venus (bottom middle). Author’s own work.

For the planets, I used exactly the same method as with the Moon. The hardest part is finding the planets in the night sky. If you are unfamiliar with night sky then their locations can be found using planetarium software like Stellarium. I must also mention that you will need some experience finding Uranus and Neptune, they are faint and you will need to be able to use a finder scope to home in on these planets.

In conclusion, I started learning astrophotography in the wrong order, webcam astronomy provides all the excitement of capturing a new world in your back garden but without the long nights, tiresome setup and ruinously expensive equipment.  So fetch that old scope out of your garage, buy a webcam and get recording I have evidence to show you wont be disappointed.

Post by: Daniel Elijah.

2 thoughts on “Video astronomy: an update

    • Thanks for that comment, I think webcam/video astronomy is probably the easiest way to get decent results out of mediocre equipment such as a small telescope and basic mount. It’s fun just looking at the video stream on the computer/camera!

Leave a Comment

Share This