Home > Stars > Blue Stars > Altair
Altair
"Alpha (α) Aquilae"
Blue Star
Right Ascension:
19h 50m 47s
Best Seen:
8/1-11/15
Declination:
8º 52' 06"
Magnitude:
0.77
Computer File:
altair
Constellation:
Aquila
Actual
Compared to Sun
Distance
16.8 l.y.
--
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:
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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.
Item
Updated
Notes
Coordinates
07-15-2002
with SIMBAD
Distance
07-15-2002
with Hipparcos data
Actual Brightness
07-15-2002
previously 9
Surface Temperature
07-15-2002
approx, with diam ~1.8 Sun’s diam
Diameter
07-15-2002
mean uniform disk size ~3.317mas (see ApJ citation below, Other info)
Mass
11-20-2002
since close to main sequence star, with mass-luminosity rel: L = M3.5
Surface Gravity –
Surface Composition
–
OK for all stars
Spectral Type
07-15-2002
previously A7 V
Density –
Other Information
07-15-2002
07-22-02
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 ApJ,559:1155-1164, 2001 Oct. 1
Web search indicated equatorial
diameter only 14% larger, and spin is
10.4 hours. One site with this info is:
http://www.jpl.nasa.gov/releases/200
1/release_2001_150.html
2. previously: 15th brightest – BUT with
Hipparcos, these brightness “ranks”
Composition 7/30/13 Changed to 74% / 24% / 2%