Altitude — how high something is above the horizon
Altitude is the angle of an object above the horizon — 90° overhead, negative once it has set. A total eclipse at 3° may be hidden behind the skyline.
Altitude is the angle of an object above the horizon: 0° on the horizon, 90° at the zenith directly overhead. A negative altitude means the object has set. Together with azimuth it pins a point in the sky as seen from one place at one instant.
Why it decides whether an eclipse is worth travelling for
Because a total eclipse at low altitude may be one you cannot see. At 3° above the horizon the Sun is behind almost anything — a line of trees, a low building, a bank of haze — and you are looking through about fifteen times as much atmosphere as at the zenith. Right down at the horizon that figure is nearer forty.
This app shows altitude at maximum for every eclipse in your location's list, and it is the first thing to check after the obscuration. A 100% eclipse at 5° and a 100% eclipse at 60° are very different propositions. The altitude quoted is the Sun's centre.
How it is computed here
Altitudes on this site are geometric and topocentric — computed for an observer on the Earth's surface rather than at its centre, which matters for the Moon. They do not include atmospheric refraction, which lifts an object near the horizon by about 34 arcminutes. Near sunrise and sunset the true altitude is therefore slightly higher than the figure quoted, and the Sun may still be visible when this app says it is a fraction below the horizon.
That is exactly why the conventional definition of sunrise puts the Sun's centre at −0.833° rather than at 0: 34′ of refraction plus the 16′ from the centre of the disc to its upper limb. By the time the geometric altitude reaches zero, the Sun has been up for a couple of minutes.
Related
Updated 13 August 2026.