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Category Archives: Astronomy



I’ve made an episode for the 365 days of astronomy podcast. This is of course an awesome podcast you definitely should consider subscribing to. It was fun to make an episode, but I was slightly displeased with the mp3 compression rate. That’s why you can listen to a much better quality version on this page (just click on the image above).

By the way, that’s me with my daughter Gloria on that image.

Okay so you hear about a comet that’s supposed to be visible right now. It’s not very bright, but you’ve heard it should just be visible in your telescope. How do you go about finding such a celestial object? In this example we’ll use Stellarium and my Celestron NexStar 5SE telescope. The latter has a 5 inch diameter, so that pretty much limits my possibilities to the brighter comets. Especially since I live in a light polluted area, I can only dream about seeing objects less bright than magnitude 8. In fact, that’s already stretching it pretty much. Magnitude 7 is a more realistic limit (yes, the lower the magnitude, the brighter the object!).

First we fire up Stellarium, a great free open source planetarium program that runs on all major operating systems. It’s feature packed and very precise. Exactly what we need for something like a comet, which, as you may or may not know, moves through the night sky pretty fast compared to the background stars. It’s of course much much slower than a meteor, but if you take several pictures in a row, you can easily see the comet move from frame to frame. It all depends on the orbital parameters (ephemeris) of the comet, of course. Here you can see how I took a few photos of comet C/2009 P1 Garrad where the comet moves relative to the background stars in mere minutes.


Right now, comet C/2012 K1 PANSTARRS is positioned pretty good for where I live. According to Stellarium, it “shines” at magnitude 7.89. It’ll get brighter throughout the year, but maybe the ccd of my camera can gather enough photons to make this thing visible. If you’ve just installed Stellarium, make sure it has the correct location on Earth. F6 will give you the Location window:


To find current comets (and minor planets and all), go to the Configuration Window (F2) – Plugins – Solar System Editor:




Here you can specify that the Solar System Editor should [v] Load at startup. Click on the configure button next to that to configure the Solar System Editor. Navigate to the Solar System tab:


Yours may be empty at this point, because my configuration of Stellarium already loads a bunch of comets and minor planets. Click on the button that says Import orbital elements in MPC format…



At the Lists tab (see above) select Comets where it lets you choose between Asteroids and Comets. Then where it says Select the source, you choose Download a list of objects from the internet. At the dropdown control (Select a source from the list) you choose MPC’s list of observable comets. If this not an option, you can manually specify the following location in the text control that says Or enter a URL:

Now click on Get orbital elements. A new import data window should appear with a list of found objects:


Check the comet you want to find and click on Add objects. In the search window of Stellarium you can now type the name of this comet to see where it’s located in the night sky at a certain time and place. F3 will give you the search window:


The Stellarium search window is a bit of an odd duck. It suggests things you are looking for, but it doesn’t autocomplete like other software. You have to keep typing until you see what you were searching for. If there’s a list, the up and down arrows on your keyboard will let you move through the list and hit Enter when your object is bold faced. When there’s only one option left, you can simply hit Enter.

Armed with the Date and Time window (F5) you can now find a good time for observing the comet:


You can also change the date to find a better moment to watch a comet. Here for instance you can see that October this year the comet might be better visible at magnitude 5.91:


Do remember that comets are unpredictable and this figure might be off. It’s just a guess of how the comet will behave. To use the Precise GOTO feature of my Celestron NexStar 5SE telescope, I need the exact RA (right ascension) and DEC (declination) of the comet at an exact time. For this we will use the figure from Stellarium called RA/DE (of date) from the Search window:


When it’s exactly that date and time, make sure your telescope is pointed at that exact RA + DEC via the Precise GOTO menu of the NexStar computer. As this process takes at least a minute or two to complete, better start a few minutes earlier. If the apparent motion of the comet against the background stars is very high, the comet should move into your eyepiece when that exact moment arrives.

As you can see, comet C/2012 K1 PANSTARRS is well above the horizon tonight at the perfect location of Leo Minor, below the Big Dipper or Ursa Major.

Here’s an example photo of another comet (C/2011 L4 PANSTARRS) which I found exactly with the above described procedure.



Here’s a picture I made for Astronaut Abby, who is the Earth liaison for current ISS astronaut Luca Parmitano (hence the #CatchLuca twitter hashtag). It may not be the best photo ever taken, but there are some interesting things to tell about it. First of all, I use Sputnik on my iPhone to know when the ISS passes over my location, at what angle, brightness, etc. It’s an awesome little app that you can use for free!


Now a typical pass of the ISS takes 2 or 3 minutes of visibility, so I had to take a long exposure. With my un-modded Canon PowerShot SX200 IS, the longest exposure is 15 seconds. You can take pretty nice pictures with a 15 second exposure as I did here, but what if you want to take longer exposures? Well, luckily there is an amazing free firmware patch for most Canon cameras available. It’s called CHDK. I’ve mentioned it in the past, but I got a few emails asking how to get it working, so let me explain.

The easiest way to get CHDK on an SD card is by using STICK, a free utility for OSX, Windows and Linux. Now on my Mac (currenty running OSX 10.8.4) I had to use the StickML.command. This launches you into super user mode in terminal, so it will ask you for your admin password.

Screen Shot 2013-07-31 at 1.58.00 PM

If you use stick.command instead, it will fail later on, so be warned! Next an interface opens. You can simply drag an existing photo from your Canon camera on top if it to find the right firmware version for your specific camera. In Step 2, STICK will download the right firmware version of CHDK for you:

Screen Shot 2013-07-31 at 1.57.36 PM

Of couse you need a dedicated SD card reader/writer to create a bootable image. STICK does not communicate directly with your camera. Insert a blank SD card into your card reader/writer and choose the appropriate device in STICK. Next click Continue to Install Step and the card will be formatted for CHDK. Because CHDK is a non permanent patch for your camera, you can easily have two distinct SD cards; one to take pictures or videos where everything is normal, and one with CHDK on it if you need the extra features.

When all is done, eject the card using STICK and the LOCK IT! This seems counter intuitive, but yes, you have to lock the card in order to use CHDK and take pictures with it. That’s right, click the little lock in the write disabled position:


Screen Shot 2013-07-31 at 1.58.34 PM

This is just the way CHDK works. You can happily take photos with it in the locked position. Now go have fun with your camera with its extra menus. There are a lot of extra features, so try not to get overwhelmed. Basically find out how you can switch in and out of CHDK mode. In my case, that’s the Print button on the back of the camera. The usual Menu button will show an entirely different menu when you click it. If nothing else, you can use a setting such as this to make long exposures:


At first I thought my camera was limited to 59″ exposures, but it turned out that the Zoom control on top of the camera could be used to jump from seconds to minutes (and even hours, but I doubt the battery will provide enough power for that).

Back to our ISS picture…. if you expose for, say, two or three minutes, the stars will start to streak, due to the polar rotation of the planet we live on:

long exposure cassiopeia

That’s Cassiopeia and Cepheus. You can clearly see that Polaris on the top left does not streak. I took this photo also with my CHDK modded Canon PowerShot. But for my ISS photo I didn’t want the streaks, so I first polar aligned my NexStar 5SE, synced it to Albireo in the constellation Cygnus (always a nice double star to watch) and then taped my Canon PowerShot on top of the telescope with duck tape! This way the Canon would follow the Earth’s rotation during the ISS pass. It worked quite nicely, because the stars in Cygnus are still stars and not streaks. I used the M (Manual) settings of the camera to augment the CHDK 2 minute long exposure. The way this works is that even though the M exposure setting is at 1″, the camera will be overridden by CHDK and expose for two minutes. I used ISO 200, F8.0 (enough light enters the ccd chip during an average long exposure, and a small aperture like F8.0 will yield a longer depth of field), 2 second self timer (to avoid camera shake), manual focus (MF) to infinity. Then it was a matter of waiting for the ISS, but Sputnik on my iPhone had it right on the second. The ISS left Earth shadow at 02:32:19 in the middle of Cygnus.

Here we have Messier 3 again. Not as good as this attempt from a while back, but then again, I was kinda tired this evening so I didn’t take too many exposures. This is a stack of about 50 exposures (10 seconds each), handpicked from the whole viewing session. The sky was pretty light polluted (as is always the case in this area of the world), but there was no Moon to add to the light misery. Telescope was still the Celestron NexStar 5SE with a GPS module and a light pollution filter.

But… this was the first time I had my mount EQ aligned and “wedge aligned” as well when looking at a globular cluster. Because I had the new firmware installed, things changed some. I must say it is a lot easier, so I’ll explain the steps below for your entertainment.

I also got one of these, so I can take the telescope everywhere. It’s really nice to have a Celestron Power Tank instead of a mains AC-DC adapter like I used to have:

EQ aligning the telescope just starts out as usual. You can use my description here to get started. It still just starts with the usual EQ North Align (if you happen to live in the Northern hemisphere of course).

After a successful EQ North Align you can leave the starfinder on to continue with an Align Mount. This used to be called a Wedge Align, but this menu item is no longer available in the new firmware. Align Mount lets you align the mount on any object, so there’s no reason to align the wedge on Polaris anymore. How convenient!

From the alignment menu, choose Polar Align – Align Mount.

You will then have to perform the usual align (first a rough alignment with the starfinder, then centering the object with fine control) with the last object you used in the auto two star EQ North align.

Now comes the tricky part, because you will have to move the mount and the mechanical wedge tilt adjustment to re-center the object. As the hand control says: DO NOT USE THE DIRECTIONAL BUTTONS FOR THIS!

If you’ve never done this before, it might take some getting used to. When I was 12, I had a really simpe telescope without any motor control, so I had lots of experience with manually finding objects. I even managed to follow airplanes and catch the occasional satellite with nothing but manual control! Anyways, you’re gonna have to do the same to do an Align Mount. It’s not that hard, because the object is pretty much centered already. Just gradually move it into the red dot in your starfinder. It doesn’t really matter if you first move the telescope tripod or adjust the wedge tilt screw first:

When you’ve got the object dead center in the eyepiece of your telescope, hit ENTER and your telescope is now aligned even better than a standard EQ North Align. You may still have to use Precise GOTO, which is one of the best features of the NexStar telescope. It helped me find this comet and even the faintest objects. Be sure to check out Precise GOTO, because it’s such an eye-opener once you understand how it works and it means the difference between frustration (when the object you’re hunting for doesn’t show up) and success, when that faint object appears in the middle of your eyepiece, even in impossibly light polluted areas such as Utrecht, the Netherlands.

The Netherlands, badly light polluted



Comet C/2011 L4 PANSTARRS on April 20, 2013, 23:00 hours. Zeist, the Netherlands, backyard. This is a highly light polluted area and the moon wasn’t helping either. Celestron NexStar 5SE with light pollution filter, Alt-Az aligned. Found the comet using a precise goto at RA 0h21m47s, DE +58º09’58”. Meade DSI II pro ccd camera. Stack of 45 frames, stacked and processed in Nebulosity and Adobe Photoshop Elements.

Here’s a screenshot of Stellarium, which provided the exact coordinates of the comet for my location. Such a wonderful tool! I’ll describe how to easily find comets in Stellarium some other time.



ISS april 19, 2013


This is a 15″ exposure using a Canon SX 200 IS PowerShot on a tripod. All manual settings. I was warned about this pass by the wonderful Sputnik iOS app on my iPhone. In this photo you also see an overexposed Moon and several stars of the constellation Leo, through which the ISS was going at that time.

Have you ever considered updating the firmware of your Celestron NexStar? My hand control was running version NXS 4.13 and my motor control was running version 5.13, so updating my firmware was long overdue. In case you didn’t know: the Celestron NexStar 5SE contains two separate computers that each run their own firmware version. You can find the versions of your telescope’s firmware via the Utilities Version menu:

Why would you update your firmware to begin with? You can be sure that your telescope will run with more precision and less bugs with a newer version of the firmware. And amazingly, my NexStar is now more quiet than it was before! A very good reason to have updated the motor control firmware indeed! Read all about it here if you are curious.

The Celestron firmware update software is available only for the Windows operating system. So I decided to update my telescope’s firmware via Parallels for OSX, since I am using a Macbook Pro with OSX.

First I had to get the correct cable(s), though. To update the telescope’s firmware, you either need an old computer that still has an RS232 serial port, or a USB-to-serial adapter. With my Macbook Pro, I had to opt for the latter.

I bought a Plugable USB to RS-232 DB9 Serial Adapter (Prolific PL2303HX Rev D Chipset) on for $12.95. You also need an rs232 cable that connects to the bottom of your hand control. Read all about it here. I got my rs232-to-handcontroller cable at our local Celestron dealer, Here you can see how that cable connects to the hand control:

I downloaded two installers from the Celestron site. One to update the motor control firmware (MCUpdate), the other to update the hand control firmware (HCUpdate). After installation, I started with the motor control update. MCUpdate allowed me to download the latest version via the web. You can see how this looks further below, where I describe the hand control firmware update, which uses a very similar procedure. I had to connect to COM3 in order to communicate with the telescope, but your COM settings may differ.

After clicking on “Begin programming”, the motor control firmware was updated. It took a few minutes to complete, during which time the hand control was in a locked state.

Updating the Hand Control firmware was very similar. Again, I had to choose COM3. But in order to update the hand control firmware, I had to hold down the INFO and UNDO buttons on the hand control while turning on the power. This resulted in the following message:

Like MCUpdate, HCUpdate also let me download the latest firmware version from the web:

After clicking “Begin programming”, the software again showed me the progress of the firmware update:

For me the whole procedure was completely painless. It took a few minutes to update each firmware version. Be sure to follow all the prompts, both from the Celestron update software and those on the hand control of your NexStar 5SE. For instance, at a certain point during the procedure I had to power cycle the telescope. But when all was finished, the Utilities Version menu happily showed me that the new versions were installed:

Messier 81

That’s M81, first time I found it in this light polluted town. Also the first time I polar aligned my Celestron NexStar 5SE. I highly recommend polar aligning your scope, especially when you’re gonna do astrophotography. Why? Because a polar aligned telescope only rotates on one axis with a single motor (which means: more precision) and the photos don’t rotate from one frame to the other. But because the alignment procedure is quite involved and not well documented in the manual (or on the internet for that matter), here’s what to do if you too live on the Northern hemisphere. PS: This is the absolute minimum. We’ll cover an additional wedge align in another post.

1) The NexStar 5SE has a wedge. This wedge must be lifted such that it’s adjusted for your latitude. In my case, I live at latitude 52º, so I align the base plate to the 52º mark. You can do this during day time:

Wedge latitude align

2) Setup your telescope outside to let it adjust to the temperature and power on the NexStar computer and the GPS. Set it up in this initial position, pointing to Polaris. You can move the tripod around such that Polaris is more or less centered. It is important that you point your telescope to Polaris as good as you can.

Initial position

3) Wait until the GPS is linked:

GPS linked

4) When the GPS is linked, choose EQ North Align:

Polar alignment - EQ North Align

5) The first thing the NexStar asks you to do is “Set Alt to Index”. You need some light (e.g. from a red lantern) for this, and it means that you use the up/down controls of your NexStar hand control to align the two arrows:


When you have done this, the telescope is pointing towards the ground! This is exactly as it should be!

6) The NexStar now asks you to “Find the Meridian”. This is the tricky bit:

Find meridian

You now have to slew the telescope with the hand control’s right arrow button so that it points towards the sky AND is aligned to the meridian. In the sky, the meridian is the imaginary great circle on the celestial sphere. It passes through the north point on the horizon, through the celestial pole, up to the zenith, through the south point on the horizon, and through the nadir, and is perpendicular to the local horizon. This means you have to swing the telescope clockwise for a half turn (180° or π rad if you like math) until it points to the sky again, away from Polaris. It helps me to put my iPhone with a compass app on top of the telescope until it is aligned North to South:

Polar alignment - iPhone compass to find meridian

Your telescope now points to the sky, away from Polaris!

7) Now choose “EQ Auto Align” and align the telescope as you normally would do to two of the suggested stars:

Polar alignment - EQ AutoAlign

8) Voila! Your NexStar is now polar aligned. For more accuracy, you can still use “Precise GOTO“. In fact, that’s how I found the above Messier 81. My first trial with the regular Messier menu found nothing. But “Precise GOTO” yielded a much better result; M81, dead center!

Of course I would like to improve on this result. I think I can aim a little higher on the following, considering the equipment stays the same:

  • Find a place with less light pollution.
  • Take more pictures.
  • Also do a wedge align and generally make sure M81 stays better centered on the ccd.
  • Spend more time focusing.
  • Experiment with exposure settings. At 10″, M81 seems to “blow out” at the center. So less may be more here.

Stay tuned for another photo of M81.

Comet C/2009 P1 Garradd

Just like comet Hartley 2, I found this very faint (magnitude 8.3) comet C/2009 P1 Garrad using PRECISE GOTO on my Celestron NexStar 5SE with the exact coordinates of C/2009 P1 Garrad at that time, according to Carinasoft Voyager 4.5 software.

You can see the UTC date and time in this picture. I took a few dozen frames using my Meade DSI II pro ccd camera attached to my Celestron NexStar 5SE telescope. I was standing in front of our house in Zeist, the Netherlands, which is terribly light polluted. Finding a comet of magnitude 8.3 is pushing the limits of what can be seen in this area, so I was glad I could find it quite easily with my NexStar auto two star aligned to Vega and Altair. It was a beautiful night and the moon wasn’t up yet.

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