Star Stars · In Hercules
Rasalgethi
Rasalgethi, α¹ Herculis, is a red bright giant in Hercules: the 130th brightest star in the night sky.
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- Constellation
- Hercules
- Designation
- α¹ Herculis
- Apparent magnitude
- 2.78 · 130th brightest star in the night sky
- Spectral class
- M5IIvar
- Distance
- 360 light-years
- Highest at midnight
- early June
- Position (J2000)
- RA 17h 15m · Dec +14° 23′
A red bright giant, around 3,100 K, like Betelgeuse and Antares. About 31× brighter than the faintest star the eye can see. Gives off about 790 times the Sun's visible light. The light you are seeing left around 1666.
When to see it
On the night of Mon 7 Jun 2027, when it is highest around midnight, on each city’s own clock:
| From | Rises | Highest | Sets |
|---|---|---|---|
| London GMT+1 | 17:57 | 01:11 · 53° | 08:25 |
| New York EDT | 18:16 | 01:06 · 64° | 07:56 |
| Singapore GMT+8 | 19:16 | 01:17 · 77° | 07:17 |
| Sydney GMT+10 | 18:48 | 00:08 · 42° | 05:27 |
Common questions
- Can I see it from 50° north?
- Yes. It rises and sets, and at its highest it stands 54° up in the south.
- Can I see it from 35° south?
- Yes. It rises and sets, and at its highest it stands 41° up in the north.
- When is the best time of year to see it?
- Around early June, when it stands opposite the Sun and is highest at midnight. It comes round about two hours earlier each month, so by early September it is highest in the early evening, and in early March not until the hours before dawn.
- How far away is it, and how bright?
- It is 360 light-years away, and shines at magnitude 2.78 in our sky. From that far, the Sun would be a star of magnitude 10.0: too faint for the eye, a target for binoculars.
- Naked eye, binoculars or telescope?
- The naked eye, even from a city: at magnitude 2.78 it is brighter than the faintest stars a city sky still shows, about magnitude 4.5.
Look for
Start from Rasalhague: Rasalgethi is 5.3° west of it, three fingers at arm’s length.
Look for
From 50° north it climbs to 54°; from 35° north it climbs to 69°; from the equator it climbs to 76°; from 35° south it climbs to 41°.
Science
Rasalgethi’s surface is about 3,100 K, some 2,700 K cooler than the Sun’s 5,772 K, so its light is strongest at about 930 nm, in the infrared, past the red 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 −2.4, brighter than Sirius, the brightest star in our sky.
Did you know
Against Rasalhague, the brighter star the hop starts from: Rasalhague looks 1.9 times as bright as Rasalgethi in our sky, but Rasalhague is 49 light-years away and Rasalgethi 360 light-years, so side by side Rasalgethi would give off 29 times as much light as Rasalhague.
Science
Rasalgethi is the 106th nearest to us of the 156 stars on these pages with a measured distance. Its nearest neighbour among them in space is Saik, about 170 light-years from it; on our sky the two are 27° apart.
Look for
The Sun passes 37° south of Rasalgethi around early December, when it is highest at noon, in daylight: the weeks either side are its worst time of year. From 50° north it is above the horizon for about 14 hours a day, from 35° north about 13 and from 35° south about 11. It is 28° from the plane of the Milky Way.