Arkab Posterior
Arkab Posterior (β2 Sagittarii) is a yellow-white giant star in the constellation Sagittarius. With an apparent magnitude of 4.29 it is the 699th-brightest star in the night sky, and it is about 140 light-years from Earth.
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Facts
| Constellation | Sagittarius |
|---|---|
| Designation | β2 Sagittarii (Beta Sagittarii), HR 7343 |
| Apparent magnitude | 4.29 (699th brightest) |
| Spectral type | F2III |
| Color | yellow-white (B−V 0.34) |
| Distance | about 140 light-years |
| Right ascension | 19 h 23.2 min |
| Declination | −44.80° |
| Best month | August (at about 9 pm) |
How to find Arkab Posterior
Arkab Posterior is in Sagittarius. From 40° N it is highest in the south in August evenings, about 5° above the horizon. From 35° S it reaches about 80° in the south. Nearby bright stars: Kaus Australis (15° away), Peacock (15° away) and Sargas (19° away).
Where on Earth can you see Arkab Posterior?
Arkab Posterior is best seen in the evening in August. The table shows, for different latitudes, whether it ever rises and how high it climbs when it crosses the meridian.
| Latitude | Visibility | Highest point |
|---|---|---|
| 60° N (Oslo, Helsinki) | Never rises | — |
| 50° N (Frankfurt, Prague) | Never rises | — |
| 40° N (New York, Madrid, Beijing) | Rises and sets | 5° (south) |
| 30° N (Cairo, New Orleans) | Rises and sets | 15° (south) |
| 20° N (Mexico City, Mumbai) | Rises and sets | 25° (south) |
| 0° (Quito, Nairobi) | Rises and sets | 45° (south) |
| 20° S (Rio de Janeiro area) | Rises and sets | 65° (south) |
| 35° S (Sydney, Buenos Aires) | Rises and sets | 80° (south) |
| 45° S (Dunedin, southern Patagonia) | Rises and sets | 90° (north) |
How far away is Arkab Posterior?
Arkab Posterior is about 140 light-years from Earth. The light you see tonight left the star around the year 1890. That is about 32 times farther than Alpha Centauri, the nearest star system to the Sun.
What kind of star is Arkab Posterior?
Arkab Posterior has the spectral type F2III. Stars of class F have surface temperatures of about 6,000 to 7,500 kelvin, which makes them look yellow-white. It is a giant: it has used up the hydrogen in its core and swollen to many times the size of the Sun.
Questions about Arkab Posterior
How far away is Arkab Posterior?
About 140 light-years. The light we see today left it around the year 1890.
What color is Arkab Posterior?
Arkab Posterior looks yellow-white. Its spectral type is F2III, which means a surface temperature of about 6,000 to 7,500 kelvin.
Can you see Arkab Posterior from the Northern Hemisphere?
Yes. From 40° N it rises and sets; at its highest it stands 5° high in the south.
Can you see Arkab Posterior from the Southern Hemisphere?
Yes. From 35° S it rises and sets; at its highest it stands 80° high in the south.
When is the best time to see Arkab Posterior?
In the evening in August, when it is highest at about 9 pm. It is 4.29 magnitude, the 699th-brightest star in the night sky.