Altair is a white A7V main sequence star. The star is about 1.6 times the diameter of the sun.
The spectral type implies an effective temperature of 8100 K, a luminosity about 9 times that of the sun, and a mass almost twice that of the sun.
According to Burnham Altair is one of the most rapidly rotating stars known. The rotational speed at the equator, as determined from the spectrum, amounts to 160 km/s, which implies a rotational period of about 6.5 hours. (The equatorial rotation period of the sun is 25.4 days.) This very rapid rotation suggests that the star is very appreciably flattened by centrifugal force, so that the polar diameter might be one half of the diameter measured across the equator.