One Light
Sirius, the Dog Star — and the cat that was erased from the sky
Why the brightest star in the night sky is called the Dog Star, how far away it really is, and the short life of Felis, the cat constellation an astronomer drew in 1799.
The Dog Star
Sirius is the brightest star in the night sky. Its catalogue name is α Canis Majoris: the alpha, the brightest star, of the constellation Canis Major, the Great Dog. Its standard English nickname, the Dog Star, is exactly that: the star of the dog.
In Chinese it is 天狼星, “the sky-wolf star”. Among Chinese-speaking pet owners there is also a folk saying that a dog who has died has “gone back to 汪星”, the woof-planet. That is a figure of speech, not astronomy. But the coincidence is real: there is a star in the sky that English already calls the Dog Star.
How far away it is
About 8.60 light-years. The figure comes from the parallax measured by ESA’s Hipparcos satellite, 379.21 ± 1.58 milliarcseconds. One over the parallax gives 2.637 parsecs, and the uncertainty works out to about ± 0.036 light-years. In other words, light leaving Earth today needs about eight years and seven months to cover the distance, give or take roughly 13 days.
For comparison, Proxima Centauri, the nearest star, is 4.25 light-years away.
The cat that was drawn, then erased
In 1799 the French astronomer Jérôme Lalande had a cat drawn onto the star charts, between Antlia and Hydra. Later writers agree on this English rendering of his remark:
“I am very fond of cats. I will let this figure scratch on the chart. The starry sky has worried me quite enough in my life, so that now I can have my joke with it.”
Johann Elert Bode painted the figure, Felis, into his atlas Uranographia in 1801. Later astronomers dropped it. Its stars are faint, the brightest only about fifth magnitude, and they were folded into Hydra. The cat is gone from the charts. The stars were not removed.
What these stars are, and what they are not
A constellation is a set of coordinates and a story people told about them. It says nothing about anyone’s character or fate, and no star is a place where someone lives. Sirius is useful as a measuring rod: a real distance, measured well, that you can compare a stretch of time against.
Questions
Why is Sirius called the Dog Star?
Because it is the brightest star of Canis Major, the Great Dog. Its catalogue name is α Canis Majoris.
How far is Sirius from Earth?
About 8.60 light-years, from a Hipparcos parallax of 379.21 ± 1.58 milliarcseconds (± 0.036 light-years).
Was there ever a cat constellation?
Yes. Felis was drawn by Jérôme Lalande in 1799 and appeared in Bode's Uranographia in 1801. It was later dropped and its stars folded into Hydra.
- Sirius = α Canis Majoris, the brightest star in the night sky, with the English alias “the Dog Star”, as checked for the One Light app’s fact sheet; catalogue entry: SIMBAD.
- Distance: Hipparcos parallax 379.21 ± 1.58 mas (ESA Hipparcos); Proxima Centauri 4.25 ly from NASA.
- Felis: Lalande 1799, Bode’s Uranographia 1801. The quotation is the English rendering repeated by later writers; we have not checked it against Lalande’s French original.
- “汪星” is a folk saying among Chinese pet owners; we have not traced its origin.
Also in this series
One Light uses Sirius as a measuring rod: from the day you said goodbye, it shows how far light has travelled since. It does not say they live on a star.