A solar eclipse occurs when the Moon comes directly between the Earth and the Sun. When this happens, the Sun’s light is blocked, and the Moon’s shadow falls on Earth. During an eclipse, the Moon and the Sun appear to be exactly the same size in the sky, because although the Moon is much smaller, it is also much closer. Total eclipses occur once every 18 months around our planet. However, it is estimated that any one place on Earth only sees a total eclipse every 360 years. An eclipse is when one celestial object moves in front of another one. There are two types of eclipses, solar and lunar.
Solar eclipses
The Moon’s shadow consists of two cone-shaped areas (see Figure 1), known as the umbra (externally tangent to the Sun and Moon) and the penumbra (internally tangent to the Sun and Moon). For an observer standing between the Moon and the umbra cone summit the eclipse is total. If the observer is beyond the cone summit, the eclipse is annular (ring-like): the apparent diameter of the Moon is too small to mask the whole solar disk. For an observer standing in the penumbra, only a part of the Sun is masked: the eclipse is partial.
The most favourable conditions for a total eclipse are when the Moon is at its perigee, Earth is farthest from the Sun (around July) and when the Sun is observed near zenith. When these conditions are all met, one can have totality duration of more than seven minutes.
Lunar eclipse
A lunar eclipse occurs when Earth comes between the Sun and the Moon. This phenomenon can be seen by any observer on Earth for whom the Moon is above the horizon, and so is much more frequent. Lunar eclipses occur at the time of a Full Moon, and when the Moon is near one of the nodes of intersection between its orbit and the ecliptic plane.
Earth’s umbra is larger than the whole Moon. So, one will observe either a total eclipse by the umbra (which can be well observed), a partial eclipse by the umbra and penumbra, or a total or partial eclipse by the penumbra only. The duration of a lunar eclipse is much longer than a solar eclipse, and can take as much as six hours.
In practice, the lunar eclipse conditions are modified due to the refraction of the Sun’s rays by Earth’s atmosphere. This refraction (of 35 minutes of arc) allows some light to penetrate the cone of geometric umbra. So even during total lunar eclipse, the lunar disk is not completely dark. This grazing light is more absorbed by Earth’s atmosphere in the blue and yellow portions of the spectrum, giving a particular reddish light during total lunar eclipse.
Picture Credit : Google
