Wednesday, January 24, 2018

A Dog Star and Her Pup

After last week’s presentation on exoplanets, I was inspired to set up my scope to attempt imaging these icy January skies. Of course, direct imaging of exoplanets is far beyond the reach of my amateur scope and its suburban skies. However, I was able to image a planetary-sized object without much trouble.

Sirius, “The Dog Star” is the closest star visible to naked eye observers in Maryland’s night sky. Likewise, it is the brightest star in the night sky.  Most astronomers know that it is joined by a faint companion, Sirius B or “The Pup.”  

No ordinary star, Sirius “B” has evolved through The Main Sequence and is ending its life as a slowly cooling “white dwarf." At 7,500 miles across, it certainly can be considered planetary-sized. However, it packs about the mass of the sun in that tiny volume creating a super dense object that would never be considered a planet.

If you are like me, you grew up believing that “Sirius’ faint companion” was far beyond the reach of any instrument you might use. At magnitude 8.4 (a full 10 magnitudes fainter than its primary) and appearing as close as 3 arc seconds to Sirius, it seems forever lost in Sirius’ glare.

However, as our imaging technology moved from photographic film through CCD and CMOS chips, Sirius B moved in its 50 year orbit toward its greatest elongation in 2019. Now, is the perfect time to attempt an image.

Sirius B's 50.1 - Year Orbit  -  created with SkyTools 3
My neglected scope seemed happy as I set it up early Friday evening. I’d forgotten how heavy the OTA weighed. You can bet many of my neighbors shook their head as they arrived home from work ready to begin their weekends. A few shouted random opinions of the night’s weather. No one asked to look through the scope.

I had been meaning to begin imaging a list of close double stars in the winter sky. Mars passes very close to the earth this summer, and I need to hone my high-resolution imaging skills to best capture the event. Sirius seemed to be a great object to head the list.

Instead of using the DSLR camera I use for deep-sky imaging, I attached the ZWO ASI224MC planetary camera and pointed the scope toward Sirius. 
Wow, the seeing has been horrible this winter. Instead of presenting a still and steady blue-white beacon, Sirius randomly jumped around the field of view like an angry dog on a leash. I certainly couldn’t see the faint Sirius B on my computer screen and held little hope of successfully imaging the faint star.

Sirius unprocessed

Waiting a couple of hours for the scope to cool and Sirius to rise higher in the southern sky, I realigned the scope toward my target. Unfortunately, Sirius still jumped around the field of view, this time perhaps like an angry leashed puppy.

I dutifully began my imaging session capturing five series of 250 images. Afterwards I imaged Castor, Rigel and Sig Ori to begin my “Doubles of The Winter Sky” project. Soon, the combination of cold weather and deteriorating seeing drove me into the warmth of my house where my computer waited.

I processed my images with Registax - software designed for planetary images. Only 25 of the 250 images were useful.
Sirius - Stack of 25 Images using Registax

Once I got a decently spherical Sirius, I used the same wavelet functions that successfully nabbed me success with the Miranda image. Surprisingly, Sirius B worked its way from the glare. I could see it! The closest white dwarf to our solar system.

Sirius - Stack of 25 Images Processed with Registax Wavelets

I used Photoshop to stretch the image a bit giving me a dark sky and brighter stars. I had my Sirius B image.

If you are curious, here are the other observations from that evening. Admittedly, these images are works in progress.

Sigma Orionis

Successful astro-imaging doesn’t require dark skies or perfect seeing. With a little flexibility, one can even surprise one’s self with what the night sky reveals.

Keep looking up to clear skies.




  1. Well done! Beautiful image.

    I believe I can see Sirius B in your unprocessed image as well, popping in and out of view at about 10 o'clock. Does that unprocessed image approximate what an eyepiece view would look like? If so, you might have been able to see the "Pup" with your own eye!

  2. Thank you!

    I too believe that I can see Sirius B in the GIF animation. However, I don't think I would have seen it unless I knew exactly where to look. Quite honestly, I never looked through an eyepiece that night. I have visually observed Sirius B with a 10" scope on a night with much better seeing.


Goodbye, Orion

Amateur astronomers loathe the month of March. Daylight Savings Time steals yet another hour from our rapidly decreasing observing time....