The Dog Star & the Pup

Camera :
300 x 2 sec., stacked
Image date:

Which is the first star to become visible after sunset?

If you’re looking between December and May, the answer will be Sirius. It’s the brightest star in the whole sky. It gets is name from the Greek word “seirios”, meaning “the brilliant one”. Not named after me, then.

It can be outshone in the night sky only by the Moon, Venus, Jupiter or Mars (or that elusive supernova that we’ve been waiting four hundred years to see and still hasn’t happened).

Did you know?

1. The Sirius system is the the fifth nearest star system.

2. The Voyager 2 spacecraft, launched in 1977, is predicted to pass within 4.3 light-years of Sirius in approximately 296,000 years time.

Sirius is called the “Dog Star”, due to it being the brightest star in the constellation of Canis Major (the Great Dog). It’s a double star, only 8.6 light years away and the smaller companion, Sirius B, is known as the Pup.

What makes Sirius interesting to amateur astronomers is that the Pup is very challenging to spot, due to its very close proximity to the overwhelming brightness of Sirius A.

ComponentNicknameApp. MagClassTemp ºK
Sirius AThe Dog Star-1.47Type A9,940
Sirius BThe Pup+8.44White Dwarf25,000

The magnitude difference represents a brightness ratio of 10,000:1, where the bright glare of Sirius A overwhelms the dim Pup (Sirius B), making it a challenge to find. I recall once attempting to see it visually as an observational astronomer – and failing.

I was able to locate the Pup for the first time by stacking a number of short exposures – and it stood out immediately near the 12 o’clock position, a tiny dot just above the brilliance of Sirius A.

Because of the short exposures, no other stars appeared in the image but I had the foresight to take a long exposure to enable me to confirm that the orientation of the Pup matched its known position exactly.

I was also helped by the two stars being almost at at their furthest separation of their fifty year orbital cycle. Current separation is 11.3 arc-seconds.

Real and apparent orbital trajectories of Sirius B around Sirius A.
Because of our position relative to Sirius, we see the orbit as more elliptical than it really is.
Image credit: Wikimedia

Thanks for reading!

Images © Roger Powell
amateur astronomy in australia

Cosmic Focus Observatory

34° South

Above us only sky….

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    1. Neither can I…..

      Sadly within a few years DSN will not be receiving data of any kind from the Voyagers. The imaging systems were permanently switched off a long time ago and the software removed because there is nothing to image (and to conserve resources).


  1. You have the MOST interesting posts. No wonder I can’t wait to read what you post.
    Yesterday the temperature where I live near Ottawa, Ontario was – 6* F.
    Yes,, I meant Fahrenheit.

    Liked by 1 person

  2. At first glance of your title, I thought you were going to write something about Procyon, the brightest star in Canis Minor, and sometimes called the “Little Dog” Star, …as you know, not far in the sky from Sirius. I perked up, because some years ago we named our Carin Terrier …Procyon, or Procy, for short! Great info about Sirius A & B!. M 🙂

    Liked by 1 person

    1. Thanks. I had a feeling this post might attract your attention. I thought maybe you may have attempted to see “the Pup” visually.

      I think the Canis Major constellation is known as the “Greater Dog” and Canis Minor is the “Lesser Dog”. Procyon apparently means “before the dog”.

      Liked by 1 person

    1. Thanks, I had the same problem with the eyepiece, which is why I wanted to find a way to image it.

      I hope you keep trying while the separation gap is at its widest. Maybe an internet search to find out how others have seen it?



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