The Sun is about 400 times larger than the Moon and is also 400 times further from the Earth than the Moon, causing them to appear nearly the same size as seen from the Earth. Slight variations in the Sun and Moon`s distance from the Earth cause the Moon to appear sometimes smaller or larger than the Sun.
The Moon’s shadow has three components – the Umbra, Penumbra and Antumbra. (The Earth’s shadow has the same components, but only the penumbra and umbra play a part in eclipses.)
The umbra is less than 250 kilometres in width at the Earth`s surface, whilst the penumbra is several thousand kilometres wide. The umbra passes very quickly along the surface, allowing for a maximum totality of 7½ minutes. However, the last 7-minute eclipse was in 1973 and the next will be in 2150. In 2009 an eclipse crossed China, E. China & the Philippine Seas to the western Pacific Ocean and, at 6 minutes 39 seconds, has the longest duration of totality in the 21st Century. Shanghai is on the centre line for this event.
Solar Eclipse: 21 August 2017. It will be total for parts of North America and partial from Europe. From Malaga view the partial eclipse from 8.45pm to 9pm.
When the moon appears large enough to completely cover the sun, a total eclipse can occur. The darkest shadow is the central umbra and anyone in this shadow will experience the total eclipse and will not be able to see the Sun.
During totality, observers can see solar prominences, the faint inner solar atmosphere (chromosphere), and the Sun’s brilliant outer atmosphere (coronal halo), which are too faint to be seen when any part of the bright solar disk is exposed. In addition, the sky usually darkens enough to reveal bright stars and planets while a twilight glow circles around the horizon.
The outer shadow, the penumbra, is not as dark as the umbra. Part of the Sun can be seen from within the penumbra which becomes less dark the closer you get to its outer edge. Anyone within the penumbral shadow of either the Earth or the Moon will see a partial eclipse of the Sun.
An antumbral shadow occurs when the umbra does not reach the Earth and the Moon appears too small to completely cover the Sun. The antumbra is an extension of the umbra and causes an annular eclipse. For anyone within the Moon’s antumbral shadow, the lunar disk will appear smaller than the solar disk, and the Sun will be seen as a ring (or annulus).
This bright ring of sunlight surrounding the Moon’s disk does not permit phenomena such as the Sun’s chromosphere and corona, associated with total eclipses, to appear.
Total Eclipses – These occur when the Moon travels completely into the Earth’s umbra. With the Moon’s speed of about one kilometre per second, totality may last up to 102 minutes. Time between the Moon’s first contact with the umbra and last contact, when it has completely exited the umbra, may be several hours.
The Moon doesn’t completely disappear as it passes through the umbra because of the refraction of sunlight by the Earth’s atmosphere. The amount of refracted light depends on the amount of clouds or dust in the atmosphere blocking the light. This can cause the Moon to glow with a coppery-red hue that varies from one eclipse to the next.
If only part of the Moon enters the umbra, it is seen as a partial lunar eclipse.
This type of eclipse occurs when the Moon passes through the Earth’s penumbra only. This does not cause a noticeable darkening of the Moon’s surface.
A special type of penumbral eclipse is a total penumbral eclipse. The moon is completely in the penumbra of the earth, but not in the umbra. At a total penumbral eclipse, the parts of the moon closest to the umbra are a bit darker than the rest of the moon. Total penumbral eclipses are a rare type of lunar eclipses.