## 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.

## Using Jetbrains products in a VM and on the host at the same time

I have been hacking on some libcamera experiment, and this time I had the misfortune to have to try and use a Jetbrains product in a local VM and on the host system at the same time.

Since it is practical I was using UTM shared networking, but that had the unfortunate side effect that Clion in the VM and IntelliJ on the host detected each other and refused to both be open at the same time. Incredibly annoying…

Googling I figured out that if you use the same username in the VM and on the host it will all work out. I got more and more confused as to why this feature exists, but a glimmer of hope emerged. I was not ready to change user in the VM or on the host though, since I had used some time to set up that user.

Thankfully, this detection feature uses the JVM system property user.name, to lookup the user, so adding -Duser.name=<host username> to the clion64.vmoptions file made it all work out.

Major annoyance averted!

## 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:

#### 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.

#### 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.

#### 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.

## 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.

## Adventures in creating a Snap from an LWJGL2 based game

The old Artifact is still kicking, not too long ago I created a Snap for it. Creating the Snap felt a bit like concocting a magical snapcraft.yaml and and hoping it works out. For the first few attempts the magic never works out, and the process of figuring things out tend to be tedious at best. This was no exception. Here are some of the problems I ran into, hope it helps someone else.

## Xprop missing

My first Snap attempt immediately spit out this during startup:

java.io.IOException: Cannot run program "/usr/bin/xprop": error=2, No such file or directory

This was fixed by adding these lines to my snapcraft.yaml. The layout is needed since xprop is referred to by an absolute path. See this thread for more information.

layout:
/usr/bin/xprop:
bind-file: $SNAP/usr/bin/xprop parts: mypart: stage-packages: - x11-utils ## A xrandr puzzle Next in line was this: Exception in thread "main" java.lang.ExceptionInInitializerError at org.newdawn.slick.AppGameContainer$1.run(AppGameContainer.java:39)
at java.security.AccessController.doPrivileged(Native Method)
at org.newdawn.slick.AppGameContainer.<clinit>(AppGameContainer.java:36)
at game.Artifact.main(Unknown Source)
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0
at org.lwjgl.opengl.LinuxDisplay.getAvailableDisplayModes(LinuxDisplay.java:951)
at org.lwjgl.opengl.LinuxDisplay.init(LinuxDisplay.java:738)
at org.lwjgl.opengl.Display.<clinit>(Display.java:138)
... 4 more


This was caused by xrandr not being installed in the snap, which LWJGL2 uses to find display stuff. This was fixed by adding the x11-server-utils package, which installs xrandr.

stage-packages:
- x11-xserver-utils

For debugging snaps and finding packages these commands were great.

#This allows you to look at the system as seen from the snap
snap run --shell <your-snapname>

#This will give the package that installed an executable, in this case xrandr
dpkg-query -S /bin/xrandr


I hope this helps someone else looking to get their application in a Snap.

## Expanding the disk on a QEMU run Ubuntu VM

A few days ago I started up an Ubuntu VM to run some silly experiment. Suddenly I needed a bit more space though, and instead of creating a new disk I decided to expand the current one instead. This took some time to figure out, so posting it here for my future self and others who possibly might want to do this.

Since there was nothing of real importance on this VM, I did most steps on the VM while it was running. Take backups if you attempt this and care about your data, I am not sure all of it is safe.

I am running QEMU using UTM on my M1 mac, and the .qcow2 files get put somewhere deep in the users Library folder by default. Once I found the file, I shut down the VM and did this on the host:

qemu-img resize disk-0.qcow2 50G

Then I started the VM, installed gparted and expanded the partition. df still reported the disk to be 90% full though. Eventually I figured that I also needed to expand the logical volume. The command to do this was:

sudo lvextend -l +100%FREE /dev/mapper/<volume name>

But still df reported the volume to be full. Seems the ext4 filesystem also needs to be expanded. This did the job:

sudo resize2fs /dev/mapper/<volume name>

Finally df reports lots of free space! Sweet!

At the beginning, I shut down the VM before I did the first resizing of the .qcow2 file. I am not sure that was necessary. The next time I need to expand a disk on an unimportant VM, I will try without shutting it down for sure.

## 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.

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.

I had a lot of fun this night!

## Artifact Snap and AppImage for Linux

Some time ago I added an AppImage for my old game Artifact, as an easy way of installation on Linux. AppImages have a neat architecture, and hopefully will keep Artifact running for a long time on a lot of systems. AppImages can also be run sandboxed using Firejail if you have little trust in me or the source of the AppImage.

Now, AppImages do not really have a nice centralized location where applications can be discovered. There are some initiatives, but it feels a bit crude and lacking some polish.

Snaps and their central registry on the other hand feel way more polished. If anything the content in the store often feels unpolished compared to the store. Snaps also run sandboxed by default. While this is good, it sometimes causes unexpected issues, and can be opted out of.

Making a Snap of a LWJGL 2 application was a bit of a headache, but it worked out in the end. My experience with the Snap documentation in general was good, and most of the work was a breeze after I got the game running as a Snap.

Now, go play some Artifact on Linux!

## 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!

## 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.

## 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:

## 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.