Leo I is a dwarf spheroidal galaxy among the most distant satellites of the Milky Way, lying almost behind Regulus, whose glare long made it hard to study.
At a glance
| type | galaxy |
|---|---|
| distance from the Sun | 815,000 light-years (250 kpc) |
| its light left it | 815,000 years ago |
| size in the piece | about 2,300 light-years acrossmodel |
Read off the piece’s own catalogue, the same values it draws with. Model marks a property of the piece’s galaxy model rather than a measurement.
About Leo I
Leo I was found by Albert Wilson on plates from the Palomar Sky Survey. It lies very close in the sky to Regulus, the bright star at the heart of Leo, and the star’s scattered light washes over it, so for a long time it was poorly observed. It is a dwarf spheroidal galaxy, but younger in its makeup than most: it formed stars over a long span, and has a substantial intermediate-age population.
It is far out and moving fast. Its velocity is high enough that astronomers have debated whether it is bound to the Milky Way at all. Measurements of its motion across the sky suggest it passed close to our galaxy in the past and is now heading outward, and its pull has been used to weigh the Milky Way’s dark halo.
What you see in the piece
In the piece it is a faint swarm of warm-coloured stars far above the disc. From Earth it would sit next to Regulus; fly out and the bright star, near the Sun, is left behind long before you reach the galaxy.
Measured or modelled
Whether Leo I is bound to the Milky Way depends on the mass of the Milky Way’s halo, which is itself uncertain.
Questions
Where is Leo I in the sky?
Leo I lies very close to the bright star Regulus in Leo, whose glare makes the faint galaxy hard to observe.
How far away is Leo I?
Leo I is 815,000 light-years (250 kpc) from the Sun, so its light left it 815,000 years ago.