57 Hydrae
57 Hydrae is a blue-white star, far hotter than the Sun, in the constellation Hydra. It is in the long, steady part of its life, making helium from hydrogen in its core, as the Sun is.
How far
450 light years
The light you see from 57 Hydrae tonight set off about 450 years ago. Everything we know about it is that much out of date.
At this distance the figure could be out by a tenth or so.
How bright
81 Suns
It gives out 81 times as much visible light as the Sun. It can just be seen by eye from a really dark place.
Astronomers put its brightness in our sky at magnitude 5.76. Smaller numbers are brighter, and the faintest stars the eye can see are about 6.
How hot
About 10,000 K
That is the temperature of its surface, worked out from its spectral type, B9.5V, 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. For stars as hot as this, colour is a poor thermometer, because most of their light is ultraviolet, so 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.
57 HydraeThe 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)
- 57 Hydrae
- Hipparcos catalogue
- HIP 72378
- Henry Draper catalogue
- HD 130274
- Spectral type
- B9.5V
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.