15 Monocerotis
15 Monocerotis is a blue star, among the hottest there are, in the constellation Monoceros.
How far
920 light years
The light you see from 15 Monocerotis tonight set off about 920 years ago. Everything we know about it is that much out of date.
Distances this great are hard to measure, and this one could be out by a fifth or more.
How bright
950 Suns
It gives out 950 times as much visible light as the Sun. It can be seen by eye away from bright lights.
Astronomers put its brightness in our sky at magnitude 4.66. Smaller numbers are brighter, and the faintest stars the eye can see are about 6.
How hot
About 37,000 K
That is the temperature of its surface, worked out from its spectral type, O7, with a standard table of how hot stars of each type are. It is a guide and not a measurement, and could be out by a tenth or so. Its colour alone would suggest only about 14,000 K. Dust lying between us and the star reddens its light, the way the air reddens the setting Sun, so for this star the type is the better guide. The Sun's is 5,772 K. Hotter stars are bluer and cooler stars are redder, the same way a poker in a fire goes from red to white.
15 Monocerotis, as it looks through the dustThe Sun
In your sky now
Working it out…
Its names
It has no name of its own. Its name by constellation is a number and the constellation it is in, from the catalogue of John Flamsteed, the first Astronomer Royal.
- By constellation (Flamsteed)
- 15 Monocerotis
- Hipparcos catalogue
- HIP 31978
- Henry Draper catalogue
- HD 47839
- Spectral type
- O7
Where this comes from
Distance, brightness, colour and spectral type are from the HYG star database, version 4.4, by David Nash, shared under a Creative Commons Attribution-ShareAlike 4.0 licence. Its distances are those measured by the Hipparcos satellite. The temperature is read from the spectral type with the table of Pecaut and Mamajek (2013), and the words are written for this site.
To read more: Colour and brightness, How stars live and die, Measuring distance.