Sirius B — A New Pup in My Life

Aaah-ooooooooooh! Let me howl it to the world. I finally saw "the Pup," the companion to the Dog Star, Sirius. Here are some tips on you can see it, too.

Dog Star Dwarfs the Pup!

The "Pup" hides in the glare of Sirius. Now — and for the next couple years — it pokes its head into better view.
Bob King

Saturday night the phone rang. The words "Unknown Caller" glowed on the landline phone screen. "Has to be a spam call," I thought. Then I looked at the number and noted that it was local. Against my better judgement I lifted the receiver and answered a tentative "Hello ...?"

"Hi Bob," a familiar voice said. It was my friend Jim, a real human and fellow amateur astronomer.

"I've got Sirius B in the scope right now and it's really obvious. Would you like to come over?" Would I?! I told him I'd get in the car right now.

"Be there in two minutes," my voice trailed off.

Dog Eat Dog Pair

This photo, taken earlier this year (2017), comes very close to showing the true appearance of brilliant Sirius and diminutive Sirius B through a telescope both in brightness and apparent separation.The two are currently about 10″ apart. North is up, east to the left.
Gabriela and Fabio Carvalho

After explaining to my wife that despite untold hours under the sky, I'd never seen the Pup, the informal name for the white dwarf companion to Sirius, the sky's most brilliant star, I was out the door. I've tried finding it with a variety of telescopes ever since I was a teen, but the dwarf has always eluded me. Either it was too close to Sirius and swamped in its glare or jittery seeing mushed the two canines into a single unresolvable blob. Sirius never rises higher than 26° altitude from my home, and serene air is as hard to come by as a good January tomato.

Even in great seeing, the magnitude difference makes splitting the pair a worthy challenge. The Dog Star shines at magnitude –1.46 and the Pup at +8.4, a difference in brightness of 10,000 times. Why would anyone bother? Amateurs would! We bother a lot because we like to see real stuff with our own eyes. To witness how the universe is put together and even at times to see it fall apart.

Feeling Diffracted

A few years back in 2008, the Pup and Dog Star were considerably closer. This image illustrates how diffraction spikes can sometimes get in the way of the star and make it impossible to see even on an ideal night. Sirius B is smaller than Earth but 98% as massive as the Sun. A 150-pound person standing on its surface would weigh 50 million pounds!
Johannes Schedler / panther-observatory.com

I arrived at Jim's place and stepped up to his 18-inch homemade Dob fitted with an eyepiece providing 300×. The air was calm, the sky partly cloudy, and the stars appeared as still as sleeping babies. I knew to look for Sirius B a short distance to the northeast of the primary. Jim described it as obvious and located just below a prominent diffraction spike sticking out like some luminous cactus spine due east of Sirius A.

OMG — there it was!

It took only a little effort to uncover this shyest of suns, but once seen, it was easily acquired again and again. For fun, we upped the magnification to 600×, and while the seeing degraded at bit, the white dwarf became even more obvious. It's one thing to read that Sirius A is 1.75 times larger than the Sun and 26 times more luminous, but when you see it next to Sirius B, a star 360 times fainter than the Sun and 400 miles smaller than the Earth, you begin to appreciate how radically different a white dwarf is from an average main sequence star.

I found it even more amazing to behold two stars that on average are only as far from one another as Uranus and the Sun, a distance of about 20 a.u. To see the pair is to sense something of the scale or our Solar System as seen from Sirius, 8.6 light years away.

Collaring the Dog Star

If you've never tried to see Sirius B, there's no better time than now through 2020, when the star will be at or near its greatest separation from Sirius A. The dwarf currently sits a hair more 10″ east-northeast of the primary; maximum separation of 11″ occurs in the year 2019. With an orbital period of 50.1 years, the Pup reached reached minimum separation of 3″ in 1994 and will again in 2044.
Jerry Lodriguss

While an 18-inch proved handy in making an astronomical wish come true — thank you, Jim! — a large scope isn't required to split these inseparables. I've seen reports of amateurs cracking them with 8-inch and occasionally even with 6-inch telescopes. The keys to success are these:

  • Excellent seeing: Walk away and look at something else if Sirius shimmies and shakes in the scope. Check every clear night till the seeing allows.
  • High magnification: You'll need at least 300× to get enough dark sky between the two stars to pry them apart. More is better!
  • Knowing exactly where to look: Keep the orbital diagram featured here handy to know where to focus your gaze. If your reflecting telescope uses a standard spider mount for the secondary mirror, stars will produce diffraction spikes. Make sure when searching for Sirius B that one of those spikes doesn't block the star from view.
  • Clever tricks: When seeking its companion, place Sirius just beyond the edge of the field or fashion a simple occulting bar for your eyepiece and tuck Sirius behind it. Both methods block the overbright star's ferocious glare, making it easier to coax out the fainter Pup.
View from the Other Side

This artist's impression shows how Sirius and its companion might appear during an interstellar flyby. The binary is close enough to Earth that most of the constellations would look the same including the Summer Triangle. Our Sun would appear as a 2nd-magnitude star.
NASA / ESA / G. Bacon (STScI)

I thoroughly enjoyed seeing Sirius B, and now that I know what to look for, I hope to find it in my own 10-inch scope. After all, the timing is good. If you've never seen the Pup, it will be at or near maximum separation for the next few years. Take advantage of a stellar opportunity to see the most famous pair of dogs in the sky. Steady skies!

13 thoughts on “Sirius B — A New Pup in My Life

      1. Anthony BarreiroAnthony Barreiro

        No, not yet. A couple of years ago a friend saw the pup through an 11-inch schmidt cassegrain, and several other people saw it, but I couldn’t. I suspect that either my eyeglasses or very mild cataract caused extra glare that prevented me from seeing it. I’ll keep pestering friends with big scopes to try.

  1. David-Green

    Hi Bob. I’m just curious: When you mention apertures regarding seeing the Pup, I assume you are talking about reflectors. Would using a high-end refractor perhaps allow for seeing the Pup with less aperture? Thanks!

    1. Bob KingBob King Post author

      Hi David,

      Yes, I think it would be possible, but I don’t know what the minimum size might be. I suspect you’d see it now in a 6-inch refractor.

  2. Alan-Harris

    My own story of seeing “the pup” is worth repeating. Back about 1977 and again a year or two later, I was observing Saturn’s satellites with the Mt. Wilson 100″ telescope. In 1977, my goal was to monitor the brightness of Iapetus as it passed through the shadow of Saturn’s rings, and in 1979/80 I was monitoring Janus and Epimethius at the time of the ring plane crossing. For both, I had build a coronagraph to eliminate diffraction and scattered light from the nearby intensely bright Saturn itself. On the first night of observation, I thought it would be a fun test to have a look for “the pup”, so in the October morning with Sirius well up in the sky, I had a look. Needless to say, Sirius in a 100″ telescope is, well, seriously bright. But there is was, more or less like the pictures in this article, and at about the same position angle, nearly a full orbit earlier. I was set up for photography but didn’t take a picture, as I expect the dynamic range of the high contrast emulsion I was using would be totally saturated by Sirius before showing “the pup”. But it was a memorable sight.

  3. eric.rachut@med.va.gov

    Within the last few years Sirius B was picked up with a Takahashi five inch triplet refractor from the Bay area in California. I have been trying with a 260mm (10.23 inch) Klevtzov catadioptric (Vixen VMC), but seeing has not cooperated yet.

    1. Bob KingBob King Post author

      Hi Eric,
      Thanks for sharing your observation. That’s quite a feat! That also answers the question another observer had about the possibility that a smaller aperture refractor might do as well as a larger aperture reflector.

  4. David AucoinDavid Aucoin

    I have seen it not so much visually as I have behind the screen of my laptyop and a ZWO ASI224MC camera on my Nexstar 8se. I was able to detect the pup several times while imaging this past winter. I used an old trick, from way back in 1977, when Dennis DiCicco made a pentagram mask for the front of his C8 to be able to photograph the pup between the spikes of the mask. On several occasions, I have imaged the pup with this set up abd have images to prove I have seen it.

  5. cypherinf

    Hi Bob,
    Emanuel from Buenos Aires here… First time commenting on your site, but frequent reader of your posts. Thanks so much for sharing your knowledge with such casual language anyone can get the message, even non-english speaking amateurs like me!
    Will be targeting the Pup with my 3-inch scope… hope to find something out there! 🙂
    Thanks again for sharing!

    1. Bob KingBob King Post author

      Thank you, Emanuel. And I hope you’re able to see it. At least Sirius is much higher in the sky for you compared to where I live. It will be a challenge, but if you find the pup, please let us know. Good luck!

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