The path in which a planet revolves around the Earth is called its orbit. The Sun’s orbit is far from the Earth and the Moon’s orbit is close. That is why the Moon keeps rotating between the Sun and the Earth.
The Earth’s shadow remains in the direction opposite or in front of the direction in which the Sun resides. Just as the Sun rotates, the shadow also rotates and its length extends beyond the lunar orbit. Because the Earth is round, the Earth’s shadow in the Moon’s orbit is also round. It always revolves around the 6th zodiac sign from the Sun. When the Moon, while rotating in its orbit, is situated in a south-northwesterly line with the Sun, that time is called Darshant period. And when the Moon reaches 6 zodiac signs ahead of the Sun, that time is called Purnimant Kaal. The image of the moon is watery, the part of it on which the sun’s rays fall appears bright. Therefore, it helps in getting rid of darkness even at night.
It has been said above that the Earth’s shadow rotates at 6 zodiac signs from the Sun and a full moon occurs when the Moon reaches 6 zodiac signs from the Sun; Therefore, a lunar eclipse does not occur during the full moon when the Moon separates from the Earth’s shadow. And during the full moon, when the moon falls in the shadow of the earth, at that time the sun’s rays do not fall on it; Hence the Moon becomes completely invisible, and it is called ‘Sarvagraas or Khagraas’ lunar eclipse. During the full moon, when only a small part of the moon falls in the shadow of the Earth, at that time, due to that part being invisible, it is called ‘partial eclipse’. That’s why lunar eclipse occurs only on full moon day.
What to do and what not to do during lunar eclipse:
Food and drink: Food and drink should be avoided during the lunar eclipse. It is a religious belief that by not eating food at this time, the body does not have to face unnecessary heat and disorders.
Chanting Mantra: It is appropriate to chant mantra during lunar eclipse. There is a religious belief that chanting mantra purifies the body and mind and can protect one from negative powers.
Donation: Donating at the time of lunar eclipse is important from religious point of view. It is appropriate to serve and provide help to other people by donating.
Meditation and religious thoughts: Meditation and religious thoughts during lunar eclipse increase religious enthusiasm and peace. It is advisable to maintain self-discipline at this time.
source: https://www.sanatanjyoti.com/blog/chandragrahan/1335