Page 5 - Dream June 2020

ANNULAR S LAR ECLIPSE COVER STORY Annular S lar Eclipse:
Annular S lar Eclipse:
21 June 2020
SArvind C. Ranade
ince antiquity, there have been solar and lunar eclipses. Last year there was an annular solar eclipse on 26 December, visible from southern parts of India. The upcoming annular solar eclipse of 21 June
2020 will be visible from parts of northern India.
An eclipse is a shadow play, in which one astronomical body gets obscured by another from an observer as a third body comes between. From Earth we can see two types of eclipses; one is solar eclipse in which the Earth passes through the shadow of the Moon on the day of new moon, while the other is a lunar eclipse in which the Moon passes through the shadow of the Earth on the full moon night. Both the Earth’s and Moon’s shadow is not uniformly dark but has two distinct regions called the umbra and penumbra. The umbra region is the darkest and forms the middle of the shadow while the penumbra, which forms the outer region, is much lighter. For
this article, we will restrict to solar eclipses only.
A solar eclipse occurs when the Moon comes between the Earth and the Sun in a straight line on a new moon. Depending on the positions of the three, there can be four types of solar eclipses: (i) Total solar eclipse, in which certain region of the Earth passes through the umbra of the Moon; (ii) Annular solar eclipse ,in which certain region of the Earth passes through the antumbra – the region from which the Moon appears entirely within the disc of the Sun, with a bright ring visible around the Moon body; (iii) Partial solar eclipse, in which certain region
of the Earth passes through the penumbra of the Moon; and (iv) Hybrid eclipse, a rare type of solar eclipse that changes its appearance – from total to annular – depending on the observer's location along the central eclipse path. Compared to total and the annular solar eclipses, a hybrid eclipse is very rare. The next hybrid eclipse will occur on 20 April 2023 but will not be visible from India.
In early 17th century, German astronomer Johannes Kepler had proved that all the planets move in elliptical orbits around the Sun. It implies that when the Sun comes very
close to Earth (perihelion), it looks bigger than when the Sun is farthest from Earth (aphelion).In between, the apparent angular size of the Sun varies from 32’ 32’’ (32 arcminutes and 32 arcseconds) and 31’ 27’’ (31 arcminutes and 27 arcseconds). It happens once in a calendar year of 365 days.
The Moon also revolves around the Earth in an elliptical orbit. Hence, the Moon also comes very close to the Earth at perigee with apparent angular size of 34’ 06’’ (34 arcminutes and 06 arcseconds) and moves to the farthest point at apogee with 29’ 20’’ (29 arcminutes and 20 arcseconds). This happens once in 27.32 days as Moon takes 27.32 days to complete one revolution around the Earth. These
june 2020 / dream 2047
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