Solar eclipses

The Sun is about 400 times wider than the Moon and about 400 times farther away, so the two look almost the same size.

The Moon in front of the Sun

A solar eclipse happens when the Moon passes between the Sun and Earth and its shadow lands on Earth. That can only happen at new Moon. Like lunar eclipses, solar eclipses need the new Moon to fall near a node; otherwise the Moon passes above or below the Sun as seen from Earth, which is what happens most months. NASA notes that solar eclipses happen about as often as lunar ones. The difference is where you can see them. A lunar eclipse is visible from half the planet, while the Moon's shadow on Earth is small, so any one place sees a total solar eclipse only rarely.

The size match is a coincidence. The Sun is about 1,392,700 km across and the Moon about 3,475 km, a ratio of about 400. The Sun is 149.6 million km away and the Moon 384,400 km, a ratio of about 389. Because both ratios are close to 400, the two disks look nearly equal: the Sun about 0.533° wide and the Moon about 0.518° on average. The Moon's distance changes along its elliptical orbit, so its apparent size changes too, and that decides which kind of central eclipse we get.

Four kinds of solar eclipse

• Total: the Moon covers the whole Sun. The sky darkens like dusk and the Sun's faint outer atmosphere, the corona, appears.
• Annular: the Moon is near its farthest point, looks smaller than the Sun and leaves a bright ring.
• Partial: the line-up is not exact and the Moon covers part of the Sun. People outside the central path of a total or annular eclipse also see a partial one.
• Hybrid: because Earth's surface is curved, the eclipse changes between annular and total along its path.

The Moon's shadow on Earth's surface is only about 480 km wide, according to NASA, so the path of totality is a narrow track. Earth turns fast enough to sweep that track a third of the way round the planet before the Sun, Moon and Earth drift out of line, but at any one spot the total phase lasts only minutes. The total solar eclipse of 8 April 2024 across Mexico, the central United States and eastern Canada gave up to 4 minutes 28 seconds. The one on 2 August 2027, crossing Spain, North Africa and Arabia, will give up to 6 minutes 23 seconds.

The model shows the line-up as seen from Earth's centre. From different places on Earth's surface, the Moon appears shifted by up to about 1° against the Sun, which is why one eclipse can be total on a narrow path and partial over a much wider area. Change the distance menu: at the closest point the Moon's disk is about 0.548° and covers the Sun; at the farthest it is about 0.491° and a ring of Sun remains. This balance will not last forever. NASA explains that as the Moon drifts away by about 3.8 cm a year, it will one day look too small to cover the Sun, but not for more than 600 million years.

How often do eclipses come? NASA says the Sun, Earth and Moon line up for an eclipse four to seven times a year, counting both kinds. They arrive in eclipse seasons, about twice a year, when the line of nodes points roughly at the Sun. A season is long enough that a solar eclipse at one new Moon is often paired with a lunar eclipse at the full Moon about two weeks before or after. NASA's tables show it clearly: the annular solar eclipse of 17 February 2026 came 14 days before the total lunar eclipse of 3 March 2026, and the total solar eclipse of 12 August 2026 came 16 days before the partial lunar eclipse of 28 August 2026.