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Cosmic Challenge: Sirius and the Pup
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Cosmic Challenge: Sirius and the Pup
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Target |
Type |
RA |
DEC |
Const. |
Mag. |
Separation |
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Sirius and |
Binary |
06h 45.1m |
-16° 42.8' |
Canis |
-1.46, 8.30 |
varies; |
Last month, I offered what many believe is one of the sky's greatest challenges, the Horsehead Nebula. This month, I am back with another classic test.
Ask an amateur astronomer to name binary stars that are difficult to resolve and one of the most common responses will probably be Sirius, in Canis Major. While there are more difficult targets, Sirius is always a perennial favorite. The challenge comes not from the close separation of the two stars in the system, however. Rather, the challenge here is from the extreme difference in the two stars' magnitude. Sirius A, a type-A1V star, is about twice the mass of our Sun, while Sirius B is a white dwarf, the last stage of a star that was once approximately five to six times our Sun's mass. Sirius B, also known as "The Pup," is believed to contain about 0.5 solar mass at present, the rest having exhausted into space over 100 million years ago. Today, all we see left from that once mighty star is the incredibly hot remnant core, a white dwarf.
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Above: Evening star map showing the location of this month's Cosmic Challenge.
Credit: Map adapted from Star Watch by Phil Harrington |
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Above: Sirius and the Pup's positions 2008-2056. Note that south is up and east is to the right, matching the view through an inverting telescope.
Credit: Chart adapted from Cosmic Challenge by Phil Harrington |
The Pup's existence was first detected in 1844 when German astronomer Friedrich Bessel noticed that Sirius wobbled ever so slightly against the background sky. From this, he reasoned that the gravity from an unseen companion must be causing the star's odd behavior. Nearly two decades later, Bessel was proven correct. American telescope-maker and astronomer Alvan G. Clark spotted the little companion on January 18, 1862, while testing an 18½-inch refractor, then the world's largest, that he had made for the University of Mississippi. Clark had selected Sirius for testing the level of chromatic aberration in the telescope; it is unlikely that he was specifically looking for the companion or that he even knew of Bessel's conclusions.
Sirius B measures no more than twice the Earth in diameter, yet its mass is nearly equal to the Sun's. Were we able to scoop up a teaspoon of Sirius B, transport it back to Earth and place it on a scale, we would find that it weighs several tons. Such is the stuff of white dwarfs. Eventually, Sirius B's energy emissions will ebb and cool, leaving just a cinder of super-dense carbon. What do you get when you compress carbon under extreme conditions for eons of time? You get a diamond. Yes, eventually, Sirius B will become a diamond roughly the diameter of Earth!
Spotting Sirius B takes the just the right combination of excellent optics, both in the telescope as well as in the sky. If the sky's optical behavior -- that is, seeing -- is uncooperative, then even the finest telescope optics will fail to resolve the Pup. Fortunately, things are getting easier. That's because Sirius B is heading toward the apastron point in its 50-year orbit around Sirius A. Over the course of half a century, the separation of these two stars varies from 3 arc-seconds to 11.5 arc-seconds. The pair appeared closest in 2000 and have been widening ever since. Both will continue to grow apart until next year, after which, they will close on each other. The table below lists the separation and position angle of Sirius B over the next several years.
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Year |
Position Angle (°) |
Separation (") |
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2020.0 |
68.3 |
11.15 |
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2021.0 |
66.5 |
11.22 |
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2022.0 |
64.6 |
11.27 |
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2023.0 |
62.7 |
11.28 |
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2029.0 |
51.1 |
10.57 |
Even when the separation is widest, seeing the Pup takes strategy. Beyond steady skies and high magnification, determine where the companion should be in the view relative to Sirius itself, and then move Sirius just out of the field. Keep in mind that, however, that depending on your eyepiece, edge distortions could distort the Pup out of existence. Therefore, many use an occulting bar across the center of the field to hide the glare of Sirius. Rotate the eyepiece around until it matches the Pup's position angle, which is currently toward the east-northeast. Incidentally, if you are using a Newtonian or Cassegrain reflector that has a spider mount holding the secondary mirror in place, double check that a diffraction spike from the spider does not inadvertently cover the star.
Here is a great capture of Sirius and the Pup by CN'er Thomas Ashcraft, which he shared in the Deep Sky Observing forum last January. He imaged the pair back on January 24, 2012, using a Celestron C14, ZWO 224 MC camera, and a Luminence filter. He also created a wonderful short video showing the visual appearance. You can view that on his YouTube channel here.
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Above: Sirius and the Pup. Photo
copyright by Thomas
Ashcraft. Used with permission. |
Give the
Pup a try when Sirius is highest in the southern sky, but again, wait for those
nights when exceptional seeing. Be sure to begin your hunt before the sky fully
darkens, since a twilight sky will help absorb some of Sirius's glare. Sirius B
is magnitude 8.5, so the sky does not have to be darkened fully to see it. Set
your telescope up before the Sun goes below the horizon, let the optics cool to
ambient temperature, and then as you are waiting for twilight to wane, focus on
Sirius and see what you discover.
Have a favorite challenge object of your own? I'd love to hear about it, as well as how you did with this month's challenge. Contact me through my website or post to this month's discussion forum.
Until next month, remember that half of the fun is the thrill of the chase. Game on!
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About
the Author: |
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Phil Harrington's Cosmic Challenge is copyright 2022 by Philip S. Harrington. All rights reserved. No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder. |
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- Bob S., John Huntley, weis14 and 10 others like this
21 Comments
great article!
Attempt #1 with a 10 inch dob was a bust but I plan to try again with an occulting bar and a mask designed to shape the diffraction pattern. Fun challenge! I also plan to try with my C6.
What magnification range is suggested when trying to catch a glimpse of the pup?
Highest the atmosphere allows, however if you can't catch even a glimpse of Sirius' airy disk, then your seeing probably isn't good enough to catch a glimpse of the Pup.
My experiences regarding observing the Pup: Using a good 10 inch Newtonian, you need high-quality eyepieces that do not induce glare for seeing it. I tried for many years using some cheap Plossls, and couldn't see it, but using a Baader orthoscopic, I was able to catch intermittent glimpses of it at 400X last winter.
The seeing where I live is good, but no great; so someone with better seeing should be able to make short work of it with a 10 inch Dob.
I will be trying again with my 6 inch F/5 Starblast, as I've heard some say its visible with 5-6 inch refractors.
I think the biggest help to seeing the pup was moving south. I've spotted it multiple times here in Atlanta with a 10" Dob. I've seen it at 200x, but it certainly is easier with higher, like 350x or 400x. I never did see it in Utah, but then again I have much more experience now with collimation. It's either that or the improved seeing (again, further south, but also the temperature doesn't drop nearly as much at night, which helps).
I'm in Birmingham with conditions to Atlanta. Was Sirius up towards zenith when you saw the Pup? I have a Paradigm ED 5mm eyepiece that gives me 240x in the dob but no luck so far.
Yes it was, and it's quite helpful to have Sirius as high as it will go. I also have to set out my Dob early so the mirror isn't warm, and make sure collimation is good (star testing works best). Some nights I still can't see it, but others I can. When you first see the pup, it seems like you just saw a hint of a star -- but then you see that hint again in the same place repeatedly as you look there.
Thanks for the tip!
Unfortunately, I've pretty much missed the last dark moon period due to my wife and I being ill. We're better now, so I'm hoping to catch up at the end of the month when the moon is again absent from the sky. The good news is that dark skies aren't needed to attempt the Pup!
John
Success! Thank you, Tangerman. Equipment: 10 inch dob, 6mm plossl eyepiece with a 2x Barlow. (400x)
I've observed Sirius B a number of times in the past few years but it was through rather large truss-tube Dobs in the 20-inch range.
I've managed to catch the Pup star with my scopes from 300mm down to 100mm. The smaller apertures have worked over the past 36 months or so as the gap between the A and B stars has reached it's widest. Before that the 300mm dobsonian was the only scope that I owned that would show it.
I find around 250x magnification seems to be the optimum for this task whichever scope I'm using, oddly enough.
I have made numerous attempts to look for Sirius B. I think I spotted it during one exceptional night through my 82/1670mm refractor. I live at 50deg North, Sirius is quite low and seeing is the largest obstacle to see the companion in any telescope. This night was quite memorable (not only because of Sirius B, I got also the best view of E and F components in Trapez), and I wrote this report to keep it in my memory
https://www.fzu.cz/~...70316_ATC82.pdf
I was also lucky enough to look through the Clark's refractor that was used to discover Sirius B. Very nice intrument.
A little bit easier white dwarf is omicron2 Eri. It is also part of stellar system. No challenge for larger telescopes (like my former 250mm Newton) but very difficult in 80mm refractor. The challenge was to separate BC components of the system (B is white dwarf, C is one of the smallest known red dwarfs). It is a different challenge than Sirius B. The system is wide but the two stars are faint. Phil, this could be a good candidate for Cosmic Challenge.
This was actually the first night for which I wrote a report back in 2011
https://www.fzu.cz/~...111229_AS80.pdf
I believe I got it, but it was before the challenge was posted… back in January! I used an ES ED127 with a 2.5x luminous Barlow, I was using a 9mm ES 100 degree eyepiece after zooming in with a Baader Hyperion 8-24mm zoom. I was also using an Optilong L-enhance filter (I think). So I was at about 260x. I wasn’t so sure because the pup had a nice blue tint to it. I was expecting Sirius to have a blue tint and the pup to be white. But it was just the opposite. I was a bit puzzled because I knew I had Sirius, duh, brightest star in the sky! The relative positions had changed a little, but not much.
After seeing the picture posted above, I knew I wasn’t seeing things! The separation was not as good as in the photo, it was right up close, barely separated. It certainly was beautiful, it could just be my optics, but the pup was a deeper blue. Like that diamond that’s going up for auction this month. It seemed like there was more contrast than in the photo above. Sirius was brilliant white. I think that contrast made it easier to see. A friend was there, he’s not into astronomy, but he saw it too and was impressed!
I need to start keeping a logbook… but that’s work! I’m in it for fun and exploration… and I don’t think anyone will read my logbook after I’m gone!
I stared at it for about 20 minutes. It was a test for my mount - tracking at highest useful magnification. The iOptron AZ Mount Pro performed like a champ! I did have to adjust the alignment as I zoomed in, but once I had it centered at high magnification, I put the 9mm ES 100 degree eyepiece on and it stayed dead center for the whole 20 minutes! It was enchanting. I guess I got really lucky. The skies were as good as it gets around here, high pressure, no wind, very little turbulence in the atmosphere. I’m at 29.5984N latitude… a little south of Atlanta & Birmingham…
Since I saw the challenge, I’ve been looking for a good night to try again, but we just haven’t had any. Totally socked in the last 5 days. The only clear nights have been windy as all heck. We are supposed to have few clouds tomorrow night and again Monday and Tuesday, but it’s gonna be very windy tomorrow… 5mph on Monday and Tuesday night. Wednesday night it’ll be searching for breaks in the clouds… then 5 more days of cr**! Of course February ends on Monday… so that will be the last chance for the challenge!
I do have 15/20+1 vision in my left (dominant) eye… (the plus 1 means I got one of the 3 letters on the 10/20 line). I’m 57, when I was a kid, I had 10/20 (left) and 15/20 (right). I wanted to be a fighter pilot, but that’s another story…
BTW, I was impressed with the Explore Scientific 9mm 100 degree eyepiece. It’s $587, but I picked it up on of their 1 day sales for $287! Definitely worth the money. It feels like you can just fall right into it! I’ve always been a plain ole plossel kind of guy and just started getting into the super wide angle eyepieces. I’ve built a set with the 9mm ES 100 degree, 21mm TV ethos 100 degree, 31mm TV Nagler 68 degree and the WO (Swan) 40mm 72 degree. The ES compares well with the TV eyepieces, the WO isn’t bad, but it’s not quite in the same class. I’ve thought about replacing it with the 41mm TV Panoptic, but that’s gonna have to wait a while! I’m really impressed with these eyepieces, but for a great many things, the good ole plossels are easier to use and all you need! At least that’s my opinion, for what it’s worth!
Blue Skies & Clear Nights!
PS -> you’ve probably picked the challenge for March, but by April, we should be getting nice views of the Milky Way, perhaps there is a challenge there, near the center of our galaxy! Just a thought!
PPS: Thank you for putting together these challenges. It’s a lot of fun and provides an objective, a goal, so to speak, as opposed to just coming up with my own observation lists. Much Appreciated!
Phil,
Thanks for another great challenge--and it's been interesting reading about other people's attempts, successes, and failures. It has been too stormy here most of February to try for Sirius A and B--and when it clears off, the wind puts the seeing in the tank.
I was able to see Sirius B about this time last year on my third attempt and I found it easier to repeat the observation after my initial success, so I'd like to try it again as soon as things settle down a little bit here.
When I went for it last year I used both techniques Phil suggests in his article. I don't have an occulting bar but I do have an occulting eyepiece I made with a piece of magenta filter covering half the FOV to use to spot the moons of Mars. It worked for that purpose but Sirius A is so bright that it overwhelmed the filter. I had success with the second technique of placing Sirius A just out of the field of view.
In my sketch, Sirius A is a good way beyond the field stop but the diffraction spikes extend out to the Pup. I used my C14 at very high magnification. The seeing was only average, but transparency was good and the Dog Star was just high enough to be out of the soup.
I think I got it tonight in my CFF160. It was only there, if at all, in moments of good seeing. I'm at 44N, so Sirius never gets much higher in the sky than it is now and my southern view is over my neighbor's house, not the best by any means. However, I was able to easily split Rigel and hold both Trapezium E and F with direct vision tonight, so I am reasonably sure I spotted it.
Good seeing is rare here, but I will try to follow up once or twice more this month if the opportunity arises.
I think I must have been mistaken when I said I thought I had seen it in January. As I recall, it was about 1 an the morning and one of my last targets of the night. It was very high in the sky.
ive tried the last couple of nights with no luck - and we had clear skies with little turbulence and no joy. I do have one thing left to try… Ha filter, but at this point, I’m not overly optimistic…. So much for superior vision! I’m going out to the Brazoria National Wildlife Refuge in the next couple of weeks, weather permitting. Very dark skies. Give it one more try. I’m looking forward to trying out my new camera on this month’s (March) challenge.
Thanks Phil!
Lkealey,
Dark skies aren't necessarily helpful to see the Pup. If you start looking during twilight, the glare from Sirius A is lessened. I think Phil mentions this in his article. Also, try to look when Sirius is at its highest altitude for your location. That might help with the seeing, too.
I was just outside here up north in Canada doing naked eye astronomy looking at Sirius and other stars
I am up at 46 + degrees north
Hi Ancletto,
I found the Pup last night for the very first time. I had to exceed 300X to see it. Actually, I used 345X and it turned Sirius into a glaring disc, but it pushed the Pup out of the glare enough that I could detect it. It would dim and brighten and disappear at times as the seeing fluctuated. The author is correct in that moonlight and light pollution does not interfere in this challenge.
-Larry
Hi Ancieto,
I responded to your post in the Cosmic Challenge, but in case you did not see that, I recommend you push beyond 300X. I had to do that to see it and it does look slightly bluish.
-Larry