INTRODUCTION

A lunar eclipse is an astronomical phenomenon in which the Sun, Earth and Moon create a straight line as they move, and the Earth’s shadow cast into space falls on the Moon’s surface. A lunar eclipse is always observable from the entire Earth's hemisphere. Depending on whether the whole Moon or only a part of it enters the shadow cast by the Earth, we recognise a total, partial and penumbral lunar eclipse. During a total lunar eclipse, it is usually possible to observe a red or reddish-brown colouration of a darkened full moon. Reports of lunar eclipses have been known since ancient times. Similarly, eclipses are predicted for many centuries to come.

Lunar Eclipse

Basic information

A lunar eclipse is an astronomical phenomenon in which the Sun, Earth and Moon create a straight line as they move. At the same time, the shadow of the Earth cast into space falls on the surface of the Moon. In contrast to the solar eclipse, which is observable only from a narrow belt, on which a shadow cast by the moon falls, the lunar eclipse is always observable from the entire earth hemisphere, on which there is darkness.

If the Moon orbited the Earth in exactly the same plane as the ecliptic plane or the plane of the Earth's orbit around the Sun, the Moon would be eclipsed with each full moon, when the Earth is between the Sun and the Moon. In reality, however, the plane of the Moon's orbit around the Earth is inclined with respect to the ecliptic plane by about 5°, and therefore all three bodies get into one line only exceptionally. Therefore, the lunar eclipse is not a very common astronomical phenomenon. Nevertheless, for a given place on the Earth's surface, it is much more common than a solar eclipse. A lunar eclipse can be observed at a specific location several times a year (a solar eclipse on average once every 400 years). This is precisely because, as has already been said, the lunar eclipse is always observable at once from the entire facing hemisphere, while the solar eclipse can be seen only from a belt 100 to 270 kilometres wide and a few thousand kilometres long.

The following figure shows the relative position of the Sun, Moon and Earth during a lunar eclipse. The distances and sizes of the bodies do not correspond to reality, the Sun is much larger and much further from the Earth, the Moon is in fact also further from the Earth.

Depending on how much of the Moon's surface enters the full shadow cast by the Earth (dark grey area in the picture) and what part of the Moon's surface remains only in partial shade, we distinguish between total, partial and penumbral eclipse of the Moon.

Types of lunar eclipses

The shadow cast by the Earth into space is always large enough to cover the entire lunar surface. However, all three bodies of the Sun, the Earth and the Moon do not have to lie exactly in one line during each lunar eclipse, and a larger or smaller part of the moon's disk can enter the full shadow cast by the Earth..

Total lunar eclipse

A total lunar eclipse occurs when the entire Moon reaches the full shadow cast by the Earth. The phase of total eclipse of the Moon is, of course, preceded by the phase of penumbral and partial eclipse, during which the lunar disk slowly moves into the area of half-shadow and full shadow and is gradually obscured by the Earth. Likewise, a total eclipse is again followed by a phase of partial and penumbral eclipse, when the moon disk emerges from the shadow. During the phase of total eclipse, the Moon is irradiated only by residual light, which refracts towards the centre of the shadow in the Earth's atmosphere. Different colours of light refract in the atmosphere, so the colour of the full moon in the phase of total eclipse depends on the distance of the Moon from the centre of the shadow (from the junction of the centres of the Sun and Earth), and also on the purity of the Earth's atmosphere at the moment of eclipse. During a total lunar eclipse, the lunar full moon is most often observed in a dark orange, reddish or reddish-brown colour, but it can also be dark brown, grey or even with a bluish tinge at the edge. Probably the biggest influence on the colour shade of the darkened Moon is the volcanic dust released into the atmosphere in huge amounts during volcanic eruptions.

Partial lunar eclipse

If the Moon is further from the line between the Sun and the Earth, it does not have to get into the area of full shadow, but only part of it. In this case, the lunar disk is observable as a sickle moon throughout the eclipse, part of which more or less obscures the shadow cast by the Earth.

Penumbral lunar eclipse

During some eclipses, no part of the Moon enters the area of full shadow. In such a situation, the shadow on the moon disk or the sickle moon is not observable at all. The circular full moon is visible all the time, only its brightness decreases slightly. This effect may not be noticeable to the eye at all. Only when the Moon gets close to the area of full shadow can it be noted that it is slightly darkened on one side.

Lunar eclipse prediction

Although the lunar eclipse is not as significant and effective as a total solar eclipse, it has met with considerable human attention in the past. In ancient civilizations, the Moon played a much more important role than today. It provided enough light at night to move around the country, and especially the alternation of its phases served to measure time and was the basis of many calendars. Therefore, the sudden disappearance or redness of the full moon attracted attention and terrified. A red Moon also appears in the New Testament, foreshadowing the Apocalypse and the end of the world. Similarly, the reddening of the Moon helped Christopher Columbus, who with his accurate prediction stunned the local Indians on his fourth expedition to America and forced them to cooperate. (Europeans were already well aware of the eclipses and their cycles at the time.)