Sirius B Observing Challenge - Results


Challenge results


Alan Whitman (Okanagan Centre), published his observations in "October's dawn window for Sirius B", Sky & Telescope 126, 4 (Oct. 2013), 30-31.

Dr. Roger Ceragioli (Vancouver Centre, and University of Arizona's Steward Observatory Mirror Lab), on 2013 October 20, writes:

I wanted to report a positive sighting of Sirius B with a 145 mm refractor tonight.

You see, I have long been extremely skeptical of amateur reports of seeing Sirius B through small telescopes -- that is, less than about 400 mm.  I tried many, many times over the past 10 years using 200 mm refractors, but saw nothing.  And now I know the reason why.  I have previously seen Sirius B in a 600 mm and 400 mm reflector from the Florida Keys during the Winter Star Party in 2009.

After much fruitful discussion with Alan Agrawal, a skilled amateur observer, who alerted me to the value of using simple polished glass balls as eyepieces, I renewed the assault on Sirius B recently.  And tonight with success!

I used a 145 mm f/8 semi-apochromat of my own construction.  It has the secondary spectrum of a 150 mm f/15 achromat, but in a much more compact package.  Essential to my success tonight was the use of an aperture mask with a hexagonal opening.  This device has long been recommended by double-star observers such as W.R. Dawes.  It alters the diffraction pattern of stars from the normal bull's-eye pattern to one in which a bright star shows the Airy disk, but with the diffraction rings mostly suppressed.  Instead of rings, one gets 6 rather dim diffraction spikes around a star.  The important point is that most of the light normally seen in the immediate vicinity of a bright star is removed, and channeled into the spikes.  Faint companions near bright primary stars in close double stars are more easily seen.

But the benefits of the hexagonal mask go beyond this.  The spikes essentially disappear around fainter stars (say 3rd mag. in moderately light-polluted skies, like mine in the middle of Tucson under a full moon).  It's as if the mask contracts the images of these stars and makes them appear as simple tiny disks.  Even around a planet like Jupiter, where the spikes can be seen, the halo of scatter light that usually accompanies the image of Jupiter is significantly diminished.

So I highly recommend the use of a hexagonal mask for all double-star and lunar/planetary observing.  It really helps, even on extended objects, I think.

The second essential device for seeing Sirius B tonight was an occulting bar.  I took an old Kellner eyepiece and fitted a narrow strip of aluminum foil onto the field lens.  Kellners are helpful in this regard since the internal eyepiece focus is normally very close to the exterior surface of the field lens: this makes attaching an aluminum strip (occulting bar) easy.  Glue it onto the lens surface!  I have an old 12 mm Kellner with such a bar.

Tonight [2013 October 20] at 4 am MST, we had very tranquil skies in Tucson and the air was not cold (ca. +50F/10C).  Sirius was high in our sky and not twinkling.  It formed a good diffraction pattern in the telescope.  Sirius B has a position angle of roughly 90 degrees or so with respect to A.  So I rotated the mask such that the spikes straddled east and did not run in that direction.  Using a 2x Barlow in my telescope gives about 190x with the 12 mm Kellner.  Next, I positioned the bar so as to run N-S, with Sirius A behind the bar and blocked, but near its edge.  The periodic drive error of my Losmandy G-11 is helpful in that Sirius A could be made alternately to approach and recede from the edge of the foil all the while staying behind it.  The 6 diffraction spikes continued to be visible where they were not blocked by the occulting bar.

With this arrangement most of the interfering light from Sirius A was blocked, except for a little secondary spectrum which announced the approach of A to the edge of the foil bar.  Within a few moments of obtaining sharp focus and setting A behind the bar, on the east side of A in the expected position I saw a very faint, but quite definite little star: Sirius B.  It appeared within the circle of secondary spectrum caused by A.  Then I rotated the mask several times in succession and examined the image.  The spikes clearly rotated with the mask.  But the faint star did not so move: the spikes shifted with respect to it.  So for the first time I feel quite sure that I have seen Sirius B in one of my own telescopes, and that a 145 mm.

If I brought Sirius A out from behind the bar, Sirius B instantly vanished in the glare of A.  Even using the bar but not the hexagonal mask rendered B invisible, since the non-use of the mask greatly increased the halo of light around A.  Only the simultaneous combination of mask/bar so reduced the stray light that B showed itself, and very clearly.

So now for the first time I'm willing to credit the idea that Sirius B can be seen even in a 100 mm telescope (using the mask and bar), as the French doublestar observer, Paul Couteau says was done at Nice 50 years ago.

Cheers and all the best.

and, from 2013 October 31:

I just came in from observing.  The seeing was again very good tonight, after some days of turbulence from a storm that passed to the north of us.

I looked for Sirius B using my 145 mm f/8 semi-apo refractor, which gives excellent images.  With the hexagonal aperture mask in place and by using an occulting bar, it is quite easy to see B.  There is no doubt whatever of its visibility, and no delusion.  I could also see it even without the occulting bar to block A, but only because I knew exactly where B was.  I could not see B without the use of the aperture mask and/or occulting bar.

Recently, I also made a hexagonal mask with a greatest dimension of 100 mm (actually 4 inches).  That I tried as well tonight.  Yes, it is possible to see B with only 4" of aperture -- using the mask and the occulting bar.  Probably the same could be done for 3" of aperture, although then certainly one would be near the limits of visibility for sure and the sighting might be in question.  But it was still clear at 4", although much less plain than at 145 mm.

I used an old Celestron 12 mm Kellner eyepiece and a 2x Ultima Barlow, which give about 190x in my refractor.  The seeing must be very good, or the observation will fail.


Dr. Ceragioli's doctoral thesis in classics was on Sirius in Antiquity (Feruidus ille canis: the Lore and Poetry of the Dog Star in Antiquity, Harvard 1992), and he has contributed articles on the fascinating observational history of this star in the Journal for the History of Astronomy (see this, and its conclusion), Sky &Telescope, and other publications.

Chris Stevenson (St. John's Centre), succeeded in photographing Sirius B on 2015 February 28. He reports:

After a session of webcam-based Jupiter imaging this past saturday night (28 Feb 2015), I took a 30 frame/sec one minute clip of bright Sirius, hoping the clarity and reasonable "seeing" of that night (1-2 arcseconds) would enable Sirius B to be detectable, even without the use of a front-end diffraction mask. I'm happy to report that after processing in Registax4 (older, but this still works fine), there it was!  I used a CPC-1100 SCT housed in a SkyShed POD, a SPC900n webcam with a 3x barlow, taking1800 frames at 30fps, Registax4, with curves in Linux' The Gimp. Decent seeing (despite a cold breeze), Registax' "wavelet" processing, Sirius B being bright enough to at least register a few photons in each 1/30th sec frame, and (apparently) decent baffling by Celestron, is what made this work. And maybe some practice.


Image copyright C.C. Stevenson


Image copyright C.C. Stevenson

 Michael Boschat (Halifax Centre), managed to observe Sirius B on 2016 March 10/11, 2320-2340 UT. He reports:

Attached is a drawing I made between 2320-2340 UT tonight of Sirius looking for "B". I used my old Celestron C8, f/10, with a 10mm Tal plossl giving 200x ( FOV = 0.30 degrees ). Seeing was 2/5 on the Antoniadi Seeing scale.

 Sirius was behind tree branches, which helped to reduce it's glare some. I also kept Sirius out of the field, and used adverted vision to see those stars indicated. One was near Sirius, which I think is "B".

I had tried Rigel earlier and saw it's companion.

I also attach a field photo from a source reversing the image to try to match my drawing.

Note the fairly bright stars to the left on the photo, I used them as guide stars  to track "B" down.

On March 8 at the same time I noted the star in the same spot with my Russian Tal-1 110mm f/7.5 Newtonian at 160x using the same method.

JPEG of Drawing

 Trevor Chandler (Kitchener-Waterloo Centre), observed Sirius B on 2018 February 2018. He reports:

I was visiting my sister in the US, and I brought along the APM152/1200. The nights here have been very steady, although transparency is poor, and LP pretty bad. But a good place for doubles.

Almach was a warmer-upper with the 13mm ETH. The 9” pair were gorgeous, and the colours salmon, and a blue green, that would be right at home in a tropical sea. Then I swung to lambda Ori, and had more trouble at 4.5”. So I used a 5mm Vixen—and presto. Diffraction rings looked perfect, too. My first observation of this nearly even matched duo. Colours bluish white.

Then I saw Rigel, and thought "what the hey". I’ve never seen that pair so cleanly split. Rigel B was obvious just below its brilliant primary. Naturally, I thought if I could see Rigel B, then maybe I should try Sirius. I centered the star, and tried, and tried, but no dice. But there was a tree branch in the way.

So I swung to theta Aur. Sky Safari says this is a challenging double because the secondary is just inside the primary’s first diffraction ring. Well, it was a snap. I’ve tried to split this pair with my 11” reflector without success, but that was under Ontario skies.

I then centered the scope on 40 Eri. The bright orange primary is a K0 dwarf about 1/2 as luminous as the sun. 40EriB is 83” away (east, I think) and also easy. It’s not particularly challenging, but it’s my first ever view of a white dwarf! It was nice with the 13mm, but I couldn’t see the 11th mag 40EriC (a red dwarf). I tried the 8mm, and the 5mm, and thought I could glimpse it—but was not sure. If I did see it, it’s my first red dwarf star!

The Sirius cleared the trees. I centered it, and tried the 13mm. No dice. Then the 5mm, but it was no good. I was going to call it a night, but put in the 8mm. This EP is not one of my favorites, so I was not expecting much. But there was Sirius B, to the right of the primary (east). I’m pretty sure this was it, as I was able to see it clearly for several seconds before it disappeared in the glare. It was much farther from the primary than I expected. My first ever view of Sirius B!! What afantastic night, and a fantastic refractor.

And it’s nice to have folks close at hand who find all this stuff interesting.

Regards from central Florida,


Blair MacDonald (Halifax Centre), reports that "after five years, I've finally snagged this one". Details are available at his website Night & Day Photography.

Last modified: 
Monday, March 5, 2018 - 11:38pm