The new Cherenkov Telescope on La Palma

End of 2018 I visited the new Cherenkov Telescope on La Palma. Actually I planned to write a long article about this visit – but as it happens sometimes, other things are more important… I decided to skip this article since now there is sufficient information out there about this telescope. However, I think the images I took for this article are still worth to see and give an impression from the observation site on the Roque de Los Muchachos on La Palma. The following two links provide more information about the CTA on La Palma:

Clear skies!

An article from in the “Dark Sky Travels Magazine”!

Recently Dark Sky Travels Magazine contacted me and asked if they could publish one of my blog articles in their magazine. The article describes how one can use DeepSkyStacker to stack conventional DSLR camera RGB frames. Of course I didn’t say no and in the end it just happened and I saw my article on page 42/43 in Issue 4 of the DarkSkyTravels magazine!

I am very happy about that opportunity and the chance to share my experience this way.

Thanks and clear skies!

Easy 2D Signal-to-Noise Ratio (SNR) calculation for images to find stars without extracting the background noise (C++)

This article shows how to calculate the 2D signal-to-noise ratio (SNR). Furthermore, it demonstrates how the $SNR$ can be used to decide if there is a potential star in the image.

Long story short – I was looking for a way to detect more or less reliably if a user selected a region which contains a star. I wanted to be able to clearly distinguish between the following two images:

Solution with the CImg library

After a long journey I finally ended up with the following solution. It is based on the CImg library which in a way calculates the Signal-to-noise ratio (SNR):

CImg <uint16_t> image;
double q = image.variance(0) / image.variance_noise(0);
double qClip = (q > 1 ? q : 1);
double snr = std::sqrt(qClip - 1);

For the two images above the code gives the following results:

~/snr$ ./snr no_star.fits 
SNR: 0.0622817
~snr$ ./snr test_star.fits
SNR: 1.5373

For many people this is where the journey ends. But for some of you it may just begin :). Follow me into the rabbit hole and find out why the solution shown above actually works…

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Binoculars vs Telescopes – When to use which for bird watching

Source: Johannes Plenio,

Some opportunities are very rare to come by. Sightings of certain species of birds are even rarer. For times like these, having a useful magnification tool such as a pair of good binoculars or a telescope can come really handy. In a broader sense, both, telescopes and binoculars serve the same purpose – they make an object that is far away, appear much nearer so you can examine it closely.

When you are observing birds from a safe distance, the birds don’t get nervous or feel threatened. You can enjoy watching the birds going about their activities without scaring them. Regardless if you are a novice or seasoned bird watcher, without a good magnification tool you are quite likely to miss out on priceless moments. Let’s take a look at which of these magnification tools is best suited for bird watching under various conditions.

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NGC2175 from La Palma

LocationLa Palma / Spain
ObjectOpen cluster NGC2175
Guidingyes, QHY5-II Mono via OAG
Barlow lensnone
MountEQ6 Syntrek
Luminance8x 600s, bin: 1x1
Red7x 150s, bin: 2x2
Green7x 150s, bin: 2x2
Blue7x 150s, bin: 2x2
Total exposure~2h13m

On Wednesday, 9th January I imaged the open cluster NGC2175 the first time from La Palma. The seeing tonight again was very good – around 1.5~2″!

For post-processing I used the free software DeepSkyStacker and GIMP.

The full resolution images is available here.

Clear skies!