Sirius A&B Split at the Wilson Coulee Observatory of the RASC Calgary Centre

I teach the Royal Astronomical Society of Canada Calgary Centre’s (RASC Calgary) Youth Group with assistance from Jack Milliken.  The group is designed to introduce youth from grades 5 – 12 to visual astronomy and help them learn to navigate the night sky.  We use the Explore the Universe certificate program from the RASC National office as the curriculum.

Friday January 20th was the first meeting for 2017 for the youth group.  The group was greeted with perfectly clear skies with relatively good seeing and transparency.  Many regular group members attended and some new members arrived with their new scopes from Christmas.  Jack and I assisted the new members learning to setup their scopes, align the finder scopes, and have them start finding objects such as Venus and Orion’s Nebula.  Needless to say but I will, the new members were thrilled to be able to use their scopes and find stuff in the sky.

Most the youth group members left by 22:00 hrs.  Jack and I decided to stay and use the club’s C14 telescope to observe some “eye candy”.  We started off using a 31mm (126X) Luminos eyepiece with an OIII filter on the Orion Nebula.  It was a spectacular view of the gas cloud.  Then we switched to the 15mm (260X) Luminos eyepiece, with no filter, to see if we could spot the fainter stars in the trapezium.  We could easily spy the E and F star.  This indicated the seeing was pretty good so we decided to try splitting Sirius.

We noticed that Sirius was almost due south and was fairly steady.  Jack knew that Sirius B was further away from the primary star and seen reports from other astronomers indicating they had split the binary pair with scopes as small as 6 inches.

Jack and I have been trying to split Sirius for a few years now and Jack even longer.  So we decided to give it a try.

But first, here is some background information about the Sirius binary system to help you appreciate the effort that goes into trying to split this double star system.

Sirius A is the brightest star in our night sky.  Sirius A is also known as the Dog Star due to its location in the constellation Canis Major or the Great Dog.  The star has an apparent visual magnitude of -1.47 and is a main sequence star.  Sirius B is the first white dwarf star ever discovered and is only about the size of Earth but is very dense with an equivalent Mass to 98% of the Sun.  The star is also referred to as The Pup. The star has an apparent visual magnitude of +8.44.  The orbital period for the two stars is 50 years.

Now we need some math to help explain the difference in brightness between the primary star Sirius A and its companion Sirius B.

To determine the difference in magnitude the formula is:

X = m1 – m2 = (+8.44) – (-1.47) = 9.91

To determine the brightness factor the formula is:

CodeCogsEqn

The result is round off for simplicity.

The above calculation indicates that the primary star is over 9,200 times brighter than its companion!

The telescope we were using was a Celestron C14 mounted on a dual fork clock drive.  The telescope has a focal length of 3910mm.  The scope is outfitted with a dual speed focuser with a diagonal mirror that accepts 2 inch eyepieces.

We started off using the same 15mm (260x) Luminos eyepiece for the E and F stars.  We used SkySafari Pro on my iPhone to determine the position of Sirius B.  Jack oriented the diagonal and eyepiece to ensure the field of view would be a true left/right flip of what the app was showing.

Jack started looking for Sirius B and thought he could occasionally see it by using his adverted vision while looking to the right of Sirius A in the field of view.  I then took a turn at the eyepiece and thought the same.  The Sirius B would keep coming and going but appeared to be in the right place.  The primary star was so bright that multiple diffraction spikes would block the view plus the star was not very steady.

Jack decided to place a neutral density filter on the bottom of the eyepiece to see if that would help.  We both discovered that it blocked too much light in order to see Sirius B.

The primary star was so bright that the shimmer caused by poor seeing made it difficult to maintain visual focus very close to it. So Jack decided to reduce the magnification by replacing the eyepiece with a 22mm (177x) eyepiece with no filter. This seemed to work but it still made it hard to confirm the split.

After a short discussion on how we could create some sort of blocking mask on the bottom of the eyepiece I suggested using a polarizing filter.  Perhaps we could control the brightness of Sirius A but still keep Sirius B visible.

After a few attempts it seemed to work but Jack was not convinced.  Because the Youth Group meeting was over I left the dome to put away the some of the other scopes used by the kids and start to pack up my laptop.

I was inside the clubhouse with two other members when Jack came in with a big smile and pumping his fist exclaiming he has done it!  I quickly went back to the telescope with Jack to see it for myself.  Jack gave me a quick lesson on how he managed to do it.

Here is Jack’s trick.  We still had to use adverted vision but the key was to let your eye adjust to the brightness.  Once your eye was accustomed to the brightness, you then shift your head to the left to cause Sirius A to be blocked by the eyepiece.  As Sirius A started to be blocked Sirius B would become more visible.  We did this a number of times and to our delight, we both could confidently state we have split the Sirius binary system.

The two other club members then came to have a look and once we explained to the technique Jack had discovered, they too could see the separation.

All of us were amazed at how close the two stars were.  It was commented that the stars appeared to be a millimetre or two apart in the eyepiece.

Here is a photo from the Hubble telescope showing the two stars.

heic0516a
Image of Sirius A (the Dog Star) with its companion star Sirius B (the Pup) located to the lower left.  Image by NASA, ESA, H. Bond (STScl), and M. Barstow (Univeristy of Leicester) – http://www.spacetelescope.org/images/heic0516a/, CC by 3.0, https://commons.wikipedia.org/w/index.php?curid=477445

The Hubble photo above helps to illustrate the problem but it is even tougher than the photo would suggest!  9200 times brighter!

It was the perfect ending to a successful Youth Group meeting.

I would like to thank Jack Milliken for his editorial review.

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