Yed Prior is a cool red giant in the hand of Ophiuchus, the leading star of a close-looking pair that is no pair at all once you leave Earth.
At a glance
| type | red giant (class M) |
|---|---|
| distance from the Sun | 171 light-years (52.5 pc) |
| its light left it | 171 years ago |
| luminosity | 691 × the Sun |
| radius | 65.7 × the Sun |
| surface temperature | 3,650 K |
| constellation | Ophiuchus (Serpent Bearer) |
Read off the piece’s own catalogue, the same values it draws with.
About Yed Prior
Yed Prior, Delta Ophiuchi, is a red giant: a star that has used up the hydrogen in its core and swollen to many times the Sun’s width, its surface cooled to a deep orange-red. Its glow comes from a vast, tenuous envelope rather than a hot surface.
The name comes from the Arabic for hand, with the Latin prior, the one that goes first. With Yed Posterior just beside it, it marks the hand of the Serpent Bearer gripping the serpent. Rising first each night, it leads its partner across the sky.
What you see in the piece
From Earth the two Yeds look like a matched couple; flown out to, they separate at once, because Yed Prior lies well beyond Yed Posterior.
Questions
How far away is Yed Prior?
Yed Prior is 171 light-years (52.5 pc) from the Sun.
Why is Yed Prior red?
Its surface temperature is only about 3,650 K, far cooler than the Sun, and a cool star glows red. It is a giant, so it is still very luminous: 691 × the Sun.