Star Stars · In Crux
Imai
Imai, δ Crucis, is a blue-white subgiant in Crux: the 131st brightest star in the night sky.
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- Constellation
- Crux
- Designation
- δ Crucis
- Apparent magnitude
- 2.79 · 131st brightest star in the night sky
- Spectral class
- B2IV
- Distance
- 345 light-years
- Highest at midnight
- late March
- Position (J2000)
- RA 12h 15m · Dec −58° 45′
A blue-white subgiant, around 26,000 K, like Rigel and Spica. About 30× brighter than the faintest star the eye can see. Gives off about 720 times the Sun's visible light. The light you are seeing left around 1681.
When to see it
On the night of Tue 23 Mar 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT | Never rises | ||
| New York EDT | Never rises | ||
| Singapore GMT+8 | 19:27 | 01:17 · 30° | 07:07 |
| Sydney GMT+11 | Never sets | 01:08 · 65° | — |
Common questions
- Can I see it from 50° north?
- No. From there it never rises: you would have to travel south of 31° north before it cleared the horizon at all.
- Can I see it from 35° south?
- Yes, on any clear night of the year — it is circumpolar from there and never quite sets, though at its lowest it skims the horizon, where trees and haze will hide it.
- When is the best time of year to see it?
- Around late March, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by late June it is highest in the early evening, and in late December not until the hours before dawn.
- How far away is it, and how bright?
- It is 345 light-years away, and shines at magnitude 2.79 in our sky. From that far, the Sun would be a star of magnitude 9.9: too faint for the eye, a target for binoculars.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 2.79 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Gacrux: Imai is 2.7° south-west of it, two fingers at arm’s length.
Look for
From 50° north and 35° north it never rises; from the equator it climbs to 31°; from 35° south it is circumpolar and never sets.
Science
Imai’s surface is about 26,000 K, some 20,200 K hotter than the Sun’s 5,772 K, so its light is strongest at about 110 nm, in the ultraviolet, past the violet end of what the eye can see, where the Sun’s is strongest at 500 nm. Moved to 33 light-years, the distance astronomers compare stars at, it would shine at magnitude −2.3, brighter than Sirius, the brightest star in our sky.
Did you know
Against Gacrux, the brighter star the hop starts from: Gacrux looks 3.0 times as bright as Imai in our sky, but Gacrux is 89 light-years away and Imai 345 light-years, so side by side Imai would give off 5.0 times as much light as Gacrux.
Science
Imai is the 104th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Acrux, about 35 light-years from it; on our sky the two are 4.6° apart.
Look for
The Sun passes 50° north of Imai around late September, when it is highest at noon, in daylight: the weeks either side are its worst time of year. It is 4° from the plane of the Milky Way, inside the band a dark sky shows.