Blinking cepheid variable stars in Messier 13

Something that feels like a once in a lifetime event happened here in Bergen this spring. We had four consecutive days of clear skies, with very little wind and no moon!

Earlier on the blog I have expressed the desire to try and image Messier 13 on consecutive nights, to see if I could see the difference in magnitude in the variable stars in the cluster. Especially the variable star V1553 Her, which has a very convenient period of approximately 5 days. 4 days of observing would get me most of the period.

These 4 days were pretty late in spring (30th of March to 2nd or April), and observing had to be done after 10PM in a work week. Not ideal. Thankfully except from the usual tracking problems, there were few problems with the equipment. My own patience failed while doing focusing though, which resulted in two nights with good images, and two with not so great quality.

This was a bit problematic since I wanted to compare images over time, and since I had 40 good images from one night, and 10 from another there was a big difference in the brightness of the stars once I was done stacking images from each night. To account for this I did some brightness matching in post processing matching on the non variable stars of each frame.

The resulting 4 frame time-lapse looks like this.

I was pretty happy with this, as it shows the variability of not only one, but at least one more, and maybe even a third variable star I missed at first (Can you find it? This paper has charts to help). The change in brightness especially for V1553 Her was also much clearer then I expected. Great success!

The process to find the distance to the star from the magnitude and variability data is neat. Since V1553 Her is a Type II Cepheid (how this was determined is not clear to me, please add a comment if you know) which period is approximately 5 days the star has an absolute magnitude of approximately -1.5 according to this chart. The formula below (from here), should then give the distance \(d\).

$$ M_v = m – 2.5log((d/10)^2) $$

Looking at the images and the reference stars, a rough estimate would be that V1553 Her varies between 12 and 13 in apparent magnitude. Plugging in -1.5 for \(M_v\) and 12.5 for \(m\) gives the distance of 6310 parsecs, which is 500 parsecs off.

While I have not followed a very thorough process here, it is anyway nice to verify that my data seems to fit to reality. To get better data for deep space objects, I am evaluating to get a solid equatorial mount with either a small refractor or an 8 inch newtonian for imaging, and keep my dobsonian for visual and planetary. Once I do I hope a can revisit this project and get a time-lapse with much higher quality. Maybe do one which would also capture the really fast variables with down to 0.2 days period.



I ❤ globular clusters

I love observing globular clusters visually. There is something very satisfying about turning the focuser to try to resolve the maximum amount of stars.

On the 12th of march I did an observing session in moonlight and quite a bit of wind, and I finally learned why astrophotographers dread wind. The telescope kept shaking, and had to park my car in front of the telescope to get it to be usable at all.

That had the sad effect of blocking most of the sky I was interested in, but M3 and M13 were still visible. After doing some visual observing I did some very lucky imaging in the wind. Of about 350 exposures of M13, about 70 were decent, and 10 of those were good. Stacking those 10 gave me this image.

M13 (Hercules Globular Cluster), image using my 10″ skywatcher dobsonian, a Televue powermate 2x, and my Canon EOS RP. This is 10 exposures of 8 seconds at 12800 ISO, stacked using APP.

The star density in such a cluster can be up to 1000 stars pr cubic parsec. Imagine living there…

Astro observation log 27.12.2021

Finally clear skies and I was at a bortle 2 location. I also had my new Canon EOS RP Camera.

M 42 – The Orion Nebula again

M 42 at a bortle 2 location was great! Last time I imaged the Orion Nebula I struggled with tracking. This time I had fine tracking (for my dobsonian anyway) and I finally got pretty round stars. I got 20 good 15 second exposures at 1600 ISO. After stacking in AstroPixelProcessor and post processing in Pixelmator Pro i got this result:

Around 15 light frames, and 20 dark frames stacked.

NGC 2024 – Flame Nebula

I have tried to observe the Flame Nebula visually many times, and I have failed every time. I was therefore planning to only do some testing photos of the region. I had trouble lining up the finder scope and camera, and I therefore did some visual observing. The nebula showed up surprisingly clear. Bortle 2 skies are really something.

Once back inside I regretted not observing more carefully visually as well as taking several image sequences. The Horsehead Nebula showed up quite clearly in my images, and with the bortle 2 skies, maybe it would have been visible visually as well.

5 lights stacked of the Flame nebula (upper left), Horsehead nebula (lower right) and NGC 2023 in the lower middle center.

M 33 – Triangulum galaxy

The galaxy showed up very clearly, and I got some images. Sadly the tracking worked badly in that region of the sky, and my focus was off. Looking forward to try this again some other time.

Single M33 shot

M 1 – Crab Nebula

I also got some images of the crab nebula. My focus work was not great, and I should use my Powermate next time, to get more nebula data.

NGC 281 – Pacman Nebula

I have tried and never even gotten close to observe this visually before. This night it was visible, and I got few images that were fine. I do not have enough data to stack, but my single ok light frame looks like this:

NGC 869/NGC 884 – Perseus double cluster

This cluster is easy to find, and with little battery left, and tracking that was not working, I decided to do 2 second shots. Stacking those resulted in this, which by far is my best open cluster image to date.

NGC 869 (left) and NGC 884 (right)

Closing thoughts

All in all this was a very rewarding session, and I finally got some deep sky data that was worth it to process. The Orion nebula image turned out way over my expectations.

I am thinking about getting an equatorial mount, and maybe a guide camera, so I can take longer exposures. It was also really great to finally see some of the more difficult nebulae visually.

Here’s to hoping I get a night in 2022 that beats this one.

Observation log 18. of April 2021.

Conditions were not great, moonlight was a pain, and some red light leaked from some camera status light into all of my M3 images.

On the positive side I finally got to see M3 and M5 and also M57 (Ring nebula), and I got decent images (for me anyway) of M13 and the leo triplet.

M57 (Ring Nebula)

I have long wanted to try to observe a planetary nebula, but I think I had the size all wrong. I was looking for something larger.

In my finder scope M57 looked a lot like a star, and if it was not so easy to locate due to being in between two bright stars I would have probably scanned past it. Once I found it, the ring structure was clearly visible at medium magnification. Really neat!

I think that having calibrated my expectations now, finding other planetary nebulae will be easier.

M13 (Hercules globular cluster)

Earlier this year I ordered a 2x TV Powermate mainly for planetary observation. To test it I tried using it together with my 2″ Aero on the globular clusters and M57. It worked way beyond my expectations.

I also took 15 seconds exposure of M13 below (the most my tracking was good for). The two red spots I marked are two variable stars, which I found comparing the chart here to my image.

M13, with two marked Cepheid variable stars. These are stars are used as distance measures, since their period determine their absolute (actual) brightness.

These stars have a periodic change in brightness. The period of their change in brightness determine their absolute brightness. Then the relative brightness (the brightness observed from Earth) and the absolute brightness can be used to find the distance to the star.

It would be really nice to try and observe M13 with the same magnification over time, and see if I can catch the blinking.

Leo triplet

I observed these galaxies visually some time ago, but this time I got to take a series of pictures as well. Out of like around 20 exposures of 15 seconds, I got 6 images that were fine. After stacking this was the result. Noisy, but some structure at least.

M65 top right, M66 to left, NGC 3628 bottom

I had a lot of fun this night!

Less light pollution; better photos.

So I finally got to try to take astro photographies from somewhere with less light pollution. I still have trouble with movement from either my tracking lagging a bit, or me not having a remote control for the camera (so I cause movement in the telescope when I start the shot).

M42 – Orion Nebula again

M42 is so easy to find observe and shoot. I also finally got to see some of the Flame Nebula, by doing a 30 seconds exposure into what looked like nothing at all. It sadly did not turn out very well because of movement in the camera, but I finally saw something! Anyway, here is my M42 shot. Getting better at this!

M42 20s exposure with pretty much no editing. Increased contrast a bit and moved the black point.

M31 – Andromeda Galaxy

The moon would easily fit in this picture, but the Andromeda galaxy takes more space, so this is mostly the core and some of the arms. I think I could fit most of the galaxy if I had rotated the camera. I randomly also caught M32 (barely visible at the left edge) and M110 (in the lower right corner). Looking forward to try Andromeda with an even longer exposure, or many stacked images.

M31 30s exposure, and some editing (contrast, black point)

Astro log – Through the smog and light pollution

A month back I finally got a new stepper motor and got the tracking for my telescope working. One dark night I took it to a pretty dark spot close to Bergen and did some observations.

M42 – Orion Nebula

I have observed the Orion nebula under bad light pollution before, but this time I got to observe it with under better conditions. It was stunning. Very sharp.

The next day I took my first deep space photography ever from our apartment. The light pollution was really bad, and there was some smog as well. I also forgot that I could use a timed shot. So i think some blurring is due to the camera moving slightly after I started the exposure.

I think it turned out fine for a first:

M42 taken with a 5 – 10 seconds exposure. Very heavy light pollution. The left image is the raw image, the right ones are versions where i increased contrast and tried to remove the pollution. The latter is an attempt to make it look somewhat like what a visual observation of M42 looks like in my telescope (it is sharper when visually observed)

M1 – Crab Nebula

My original plan for the trip, was to observe M42 and the Andromeda Galaxy. I was also hoping to get to see the Flame Nebula since it was really dark. I sadly did not see any trace of the Flame Nebula so I started looking for some open clusters to look at in Taurus. While scanning for them I suddenly saw that the Crab Nebula was close, and I found it immediately. It is the first supernova remnant I have observed, and I think I saw some small amount of detail. Hoping to get a picture of it one of these days.

M31 and M110 – Andromeda Galaxy and a friend

Andromeda is a not that interesting to visually observe since it is so hard to see anything beyond the core. I think I saw some more since it was really dark, but it was very faint. These two are prime targets for a photo some day, since that should bring out some more detail.

Astro observation log

As a kid I was always very fascinated by astronomical objects. I vividly remember the first time I observed the Andromeda Galaxy in a pair of binoculars. I think I was around 14, and I had tried to find it several times before. I did not really know what it would look like in binoculars, and I remember freezing my hands off to keep it in view once I found it. Even if it was just a blurry blob it was amazing.

Fast forward 20 years, and I now have the knowledge, time and money to buy and use a telescope. I recently bought a 10 inch Dobsonian. I am still learning to to use it well, but it has so far been worth every NOK spent.

Last night was my first observing session with the telescope under not extremely badly light polluted skies. These are the objects I have observed so far.

M35 and NGC 2158 (Open cluster in Gemini)

M35 is huge, and looks great on low magnification. It was also not very hard to find by following the stars in Gemini. It would be useful with an even lower magnification eyepiece to observe this next time.

M37(Open cluster in Auriga)

Since it is far away from the closest clearly visible star, it was a bit hard to find even though it showed up pretty clear in the finderscope once I was in the right region.

M42 (Orion Nebula)

This is so far the only nebula I have been able to observe from the city. Sadly Orion was not visible when I observed in the less light polluted location. I have not yet tried filters for contrast, but M42 is still very visible, and it looks great. Looking forward to observe this with filters and less light pollution.

M13 (Hercules globular cluster)

M13 gave M42 a run for its money. M13 was easy to find (shows up clearly in the finder scope), and at low magnification it looked great. Increasing the magnification made it awesome. Suddenly thousands of starts exploded into view.

M65 and M66, part of the Leo Triplet

With the light pollution at the time, M65 and M66 were visible but with little detail. They were not visible in the finder scope, and I just randomly found them scanning from the stars in Leo. They pretty much both looked like Andromeda in binoculars. I am hoping to see some more structure next time.

I also observed some galaxy in Virgo, but I have no clue which. It seems the area is filled with galaxies, and I found one just scanning around. Pretty neat.