| Home > Stars > Blue > Altair |
Altair
Alpha (α) Aquilae
Blue Star
| Right Ascension | 19h 50m 47s | Best Seen | 8/1 - 11/15 |
| Declination | 8° 52' 06" | Magnitude | 0.77 |
| Constellation | Aquila | ||
Actual |
Compared to Sun |
|
| Distance | 16.8 ly | -- |
| Actual Brightness | -- | 10 |
| Surface Temperature | 14,400 ºF | 1.4 |
| Diameter (average) | 1.58 million miles | 1.8 |
| Mass | -- | ~ 1.9 |
| Surface Gravity | -- | -- |
| Surface Composition (by mass) | 74% hydrogen 24% helium 2% everything else |
same |
| Spectral Type | A7 IV-V | G2 V |
| Density (gram/cubic cm) | -- | -- |
What To Look For Through The Telescope
-
Recommended eyepiece: 24mm or 40 mm.
-
When people look through the telescope a bright bluish point of light should be seen.
Altair Information:
-
Altair is the 8th brightest star in the Northern Hemisphere’s night-time sky (12th brightest in night sky when including Southern Hemisphere’s bright stars).
-
Altair rotates on its axis very quickly.
a. Altair takes just 10-1/2 hours to rotate. Our smaller sun takes thirty days.
b. Since the star is gaseous, and because it spins so fast, Altair is a bit squashed: Altair’s equatorial diameter is about 14% larger than its polar diameter.
c. By comparison, Jupiter is also gaseous and slightly squashed, but its equatorial diameter is only about 3% larger than its polar diameter.
| Home > Stars > Blue > Altair |
References
| Item | Updated | Notes |
| Coordinates | 2002-07-15 | with SIMBAD |
| Distance | 2002-07-15 | with Hipparcos data |
| Actual Brightness | 2002-07-15 | previously 9 |
| Surface Temperature | 2002-07-15 | approx, with diam ~1.8 Sun’s diam |
| Diameter | 2002-07-15 | mean uniform disk size ~3.317mas (see ApJ citation below, Other info) |
| Mass | 2002-11-20 | since close to main sequence star, with mass-luminosity rel: L = M3.5 |
| Surface Gravity | – | |
| Surface Composition | – | OK for all stars |
| Spectral Type | 2002-07-15 | previously A7 V |
| Density | – | |
| Other Information | 2002-07-15 | |
| 2002-07-22 | 1. previously: “Altair rotates on its axis in just 6 ½ hours. The rotational speed at its equator is 160 meters/second. As a result, the equatorial diameter is nearly twice the polar diameter.” – BUT these speeds are debated: 118 mi/sec to 155 mi/sec. Also, Altair is flattened, but not nearly that much. See van Belle, G. T., Ciardi, D. R., Thompson, R. R., Akeson, R. L., and Lada, E. A., “Altair’s Oblateness and Rotation Velocity from Long-Baseline Interferometry,” ApJ 559, 1155–1164 (Oct. 2001) Web search indicated equatorial diameter only 14% larger, and spin is 10.4 hours. One site with this info is www.jpl.nasa.gov 2. previously: 15th brightest – BUT with Hipparcos, these brightness “ranks” |
|
| Composition | 2013-07-30 | Changed to 74% / 24% / 2% |