Penumbral lunar eclipse to occur in India on May 5; here's the science behind it

The Moon will undergo a penumbral eclipse on the intervening nights of May 5 and 6 and the event will be visible across different parts of the world. This event will begin at an estimated time of 8.45 pm (IST) on May 5 and 1 am on May 6 and skywatchers across Africa, Australia, and Asia will be able to experience it. The penumbral eclipse is part of the different stages of a lunar eclipse when the Moon transits through the Earth's shadow. 

What is a penumbral lunar eclipse?

A penumbral eclipse occurs when the Moon travels through the Earth’s penumbra or the faint outer part of its shadow. During its transit, the Moon dims slightly so the decrease in illumination could be difficult to notice. The picture below shows the Moon entering the penumbra, which is a slightly darker region formed by the Earth's shadow. 

(Image: NASA)

When the Moon is in this region, the eclipse is called a penumbral eclipse. As the Moon moves in its orbit, it enters what is called the umbra and this is the region where all direct light from the sun is blocked. It is at this stage when the Moon appears a mix of slight red and orange because only the light having longer wavelengths (red and orange) are able to pass through the edge of our planet (or its atmosphere). All other colours of the spectrum having shorter wavelengths get scattered away and fail to reach the Moon. Notably, the higher the presence of dust or clouds in the atmosphere, the redder the Moon appears. 

(Moon in the umbra appears red as the light of shorter wavelengths fails to reach it; Image: NASA)

According to NASA, the next penumbral eclipse will take place on March 25, 2024, and will only be visible across the American continents due to the Moon's position. Next up, however, are partial lunar eclipses on October 28 and September 18 this year followed by a total lunar eclipse on March 14, 2025.