OrbitLab

Eclipse Calculator

Why some eclipses have a 'ring of fire.'

Sun diameter (km)

Sun distance (km)

Moon diameter (km)

Moon distance (km)

Eclipse type

Annular eclipse (ring of fire)

What you entered

Sun diameter (km): 1391000Sun distance (km): 149600000Moon diameter (km): 3474Moon distance (km): 384400

1
Sun's angular size
(1391000 ÷ 149600000) × (180/π)= 0.5327°
2
Moon's angular size
(3474 ÷ 384400) × (180/π)= 0.5178°
3
Comparison
Moon vs Sun angular size= Annular eclipse (ring of fire)

Result

Eclipse type: Annular eclipse (ring of fire)

With these angular sizes, a annular eclipse (ring of fire).

Why some eclipses are total and others annular

Whether an eclipse is total depends on which disc looks bigger. Angular size is diameter divided by distance, and both the Moon's and the Sun's distances vary through the year.

Configuration	Moon distance	Sun angular size	Moon angular size	Result
Apogee moon	406,700 km	0.5331 deg	0.4894 deg	Annular eclipse (ring of fire)
Mean distances	384,400 km	0.5331 deg	0.5178 deg	Annular eclipse (ring of fire)
Perihelion sun	384,400 km	0.5422 deg	0.5178 deg	Annular eclipse (ring of fire)
Perigee moon	356,500 km	0.5331 deg	0.5583 deg	Total eclipse possible
Aphelion sun, perigee moon	356,500 km	0.5244 deg	0.5583 deg	Total eclipse possible

At mean distances the Moon is very slightly too small to cover the Sun, which is why totality requires the Moon nearer than average. The best case is an aphelion Sun with a perigee Moon, giving the longest possible totality of just over seven minutes.

A cosmic coincidence of angular size

The Sun is about 400× wider than the Moon but also about 400× farther away, making their angular sizes in our sky nearly identical — this coincidence is exactly why total solar eclipses, where the Moon precisely covers the Sun, are even possible.

Why some eclipses are annular instead

The Moon's orbit is elliptical, so its distance (and angular size) varies slightly — when the Moon is near its farthest point (apogee) during an eclipse, it appears too small to fully cover the Sun, leaving a bright ring: an annular eclipse.

Frequently asked questions

The Moon's angular diameter is 0.52° and the Sun's is 0.53° — is this a total or annular eclipse?

Since the Moon (0.52°) is slightly smaller than the Sun (0.53°), it cannot fully cover the Sun. This would be an annular eclipse with a thin ring of sunlight visible.

How often do total solar eclipses happen?

About every 18 months somewhere on Earth, but any specific location sees one roughly every 375 years on average. The path of totality is typically only 100-150 km wide.

Why don't we get an eclipse every month?

The Moon's orbit is tilted about 5° relative to Earth's orbit around the Sun. Eclipses only occur when the Moon crosses the ecliptic plane (at a node) during a new moon — this alignment happens about 2-5 times per year.

What is the difference between a total and hybrid eclipse?

A hybrid eclipse appears total in some parts of its path and annular in others, due to Earth's curvature changing the observer's distance to the Moon. They are rare — only about 5% of solar eclipses are hybrid.