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Canis Minor, the Lesser Dog, is one of the smallest and simplest constellations in the sky — two stars, Procyon and the much fainter Gomeisa, forming a short line east of Orion and just south of Gemini. Procyon is bright enough to be unmistakable and marks one corner of the Winter Triangle; the rest of the figure is not much more than that single line. From Central Ohio it is visible alongside Orion on winter evenings and, like its neighbours, is not circumpolar.
Finding it
Procyon sits roughly level with Betelgeuse and well east of it, forming the Winter Triangle's third point along with Betelgeuse (Orion) and Sirius (Canis Major); the three are spaced widely enough apart, and are all bright enough, that once two are found the third is easy to place by eye. Gomeisa, a full 2.5 magnitudes fainter, sits a few degrees north-west of Procyon and needs a darker sky to pick out.
The stars
| Star | RA (h) | Dec (°) | Mag | Spectral type | Distance (ly) | Name meaning |
|---|---|---|---|---|---|---|
| Procyon | 7.655 | 5.22 | 0.34 | F5 IV–V | 11.46 | Greek prokyon, "before the dog" |
| Gomeisa | 7.453 | 8.29 | 2.89 | B8 Ve | ~160 | Arabic al-Ghumaisa, "the bleary-eyed" |
Procyon is a yellow-white F-type star only 11.46 light-years away — one of the Sun's nearer neighbours — and the eighth-brightest star in the night sky as a result of that closeness rather than any unusual size. Its name is Greek, prokyon, "before the dog": because of Earth's rotation Procyon rises a little before Sirius does, the smaller dog announcing the greater one. Procyon has its own white dwarf companion, Procyon B, predicted in the same 1844 letter in which Friedrich Bessel deduced Sirius B from wobbles in stellar proper motion. It took far longer to actually see: Procyon B is fainter relative to its primary's glare than Sirius B is, and it was not directly observed until 1896, when John Martin Schaeberle found it at Lick Observatory with a 36-inch refractor — 34 years after Sirius B was caught.
Gomeisa is a much hotter, more distant star — a blue-white B-type star around 160 light-years away, surrounded by its own disc of gas that gives it faint emission lines (a "Be star"). Its Arabic name, al-Ghumaisa, "the bleary-eyed" or "the weeping one," comes from an old piece of Arabic star lore in which Suhayl (the star Canopus) crosses the Milky Way to the south and never returns, leaving his sisters — identified with Sirius and Procyon — to weep after him.
Myth and history
Canis Minor drew less independent mythology than its larger neighbour; most Greek sources fold it into the same hunting-dog imagery as Canis Major rather than giving it its own story, and Hyginus's Astronomica is the usual source cited for what little distinct material exists.
Key dates
| Date | Event |
|---|---|
| c. 150 CE | Ptolemy catalogues Procyon and Gomeisa in the Almagest. |
| 10 August 1844 | Bessel's letter predicting an unseen companion to Sirius also predicts one for Procyon, from the same kind of proper-motion wobble. |
| 1896 | John Martin Schaeberle directly observes Procyon B at Lick Observatory, 34 years after Sirius B was found. |
Related
- Orion — Betelgeuse, the Winter Triangle's third point alongside Procyon.
- Canis Major — Sirius, the greater dog Procyon is traditionally paired with.
- Auriga — Capella, on the far side of the Winter Hexagon that also passes through Procyon.