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Observer's Challenge – Sirius and the Pup

Sirius, the dog star, is in the constellation Canis Major. It is the brightest star in the night sky (mag-1.46) and during the next few months is an easy object to spot as it follows dutifully behind Orion, the Hunter. What is not quite so obvious, certainly with the naked eye, is that Sirius has a companion commonly known as the ‘Pup’.

The Pup (Sirius B) is a white dwarf star of magnitude 8.5, located, with Sirius, at about 8.6 light years from Earth. In fact, the Pup is only slightly smaller than the Earth in size, with a diameter of about 12,000 km. Sirius, by comparison, is some 2 million km in diameter!

Whilst not a naked eye star, without its proximity to Sirius it would be an easy target with some  optical assistance. But being Sirius’ companion necessarily means it will always be swamped by the glare of its far brighter companion. The picture (right) shows the Pup just to the left of Sirius. This is an image taken by Leo Aerts. See for full details.

Although Leo, based in Belgium, used a Celestron C14 for this image, of the Pup, some sources claim to have seen it from the UK in a 130 mm refractor and a 127 mm Maksutov under excellent seeing conditions. 

The diagram (lower left) is taken from Jerry Lodriguss’ excellent website, ‘Catching the Light’.

As can be seen from the diagram, the orbit of the Pup, from our perspective, is almost at maximum distance from Sirius, and still drawing away for the next year or so. Consequently, it is becoming slightly easier to observe. The challenge, either photographically or visually, is to show both Sirius and the Pup. This could be a ‘one-off’ or a series of images/drawings, as a longer-term project, over the next months/years that shows the gradual increasing separation of the two stars. It may be possible to observe the pup more easily by obscuring Sirius itself by means of an occulting bar or something similar. 

Members are encouraged to submit Images or drawings of Sirius and its Pup to their areas on the website, at They are also encouraged to send these to the Deep Sky Section Director at

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