What is a lunar day and a lunar night -- All you need to know

Chennai: India's first moon lander Vikram successfully separated from its mother spacecraft Chandrayaan-2 on Monday at 1.15 a.m., said Indian Space Research Organisation (ISRO). According to ISRO, the Vikram Lander is currently located in an orbit of 119 km x 127 km. The Chandrayaan-2 Orbiter continues to orbit the Moon in its existing orbit. (Photo: IANS)

Moon is the only natural satellite of the earth and the nearest astral body to our mother planet. Humans have been dreaming for so long about settling in the moon. A number of science fictions have talked enough about how life will be on the moon. Humans have been sending people and machines to the moon to explore it. If we think the day and night on the moon are the same as how they are on the earth, we are fully mistaken. The days and nights on the moon called lunar day and lunar night are interesting concepts in astronomical studies.

Why talk of the lunar day and lunar night

There are two important reasons why we need to understand the concept of lunar day and lunar night. If we need to think of living on the moon at some point in time, we need to be ready for the kind of life on the moon. Any lunar adventure planned must take into account the length of the lunar day and lunar night. Humans and machines had always landed on the moon during the lunar day when the moon’s surface they landed on was exposed to the sun. Lunar days are extremely hot and lunar nights are extremely cold that we can just imagine with the temperature during lunar days reaching up to 270 degrees Fahrenheit and temperatures during lunar nights dipping up to minus 280 degrees Fahrenheit.

Chandrayaan-2 and lunar day

The Chandrayaan-2 mission triggered our interest about lunar day and lunar night. The Vikram lander was planned to land on the moon’s surface during the lunar day as the extreme cold temperatures of the lunar night would be thoroughly unconducive to its activities. When the orbiter lost its signals with the Vikram lander, the ISRO and NASA continuously tried their best to connect with the lander for about 14 days. When the lunar night started, their hopes of connecting with the lander were lost once for all.

What is a lunar day and lunar night

A lunar day means the time taken by the moon to complete one rotation on its own axis. The moon is tidally locked to the earth. This means one side of the moon is always facing the earth. The other side is turned away from the earth and it is never visible to the star lookers anytime.

The lunar day lasts for 29 days, 12 hours and 44 minutes. Precisely, this is the total time taken by the moon to make one orbit around the earth.

The earth and the Moon are orbiting around the sun. They complete a full rotation around the sun in one year (365 days). While the earth’s rotation around the sun is straightforward, the moon has to rotate the earth and as the earth moves in its orbit around the sun, the moon also automatically moves around the sun while circling the earth.

By an earth day we mean the length of time earth is exposed to the sun. By night we mean the duration for which the earth does not receive the sunlight. Since the earth takes 24 hours to go complete one rotation on its axis, an earth day lasts for 12 hours and the earth night lasts for 12 hours making a full day cycle.

In case of moon, the face of the moon locked to the earth surface remains exposed to the sun for about 14 days and the other side is exposed to the sun for the next 14 days. This is why the lunar day is approximately 14 days long and the lunar night is again of the same duration.
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