5th May 2023 – Penumbral Eclipse: All You Need to Know – Poornaprajna Amateur Astronomers Club

The Full Moon of May 2023, will pass through the Earth’s shadow on 5th May 2023 causing a Penumbral Lunar Eclipse.

What causes a Lunar Eclipse?

The Moon passes behind the Earth every month, and during this time, the night-side of the Earth can see the Moon completely illuminated by sunlight, which we call, the Full Moon. Although we have a Full Moon every single month, we do not have eclipses as often.

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We can imagine the path of the Sun to be along a circle in the sky, and the same can be done with the Moon. We can imagine these circles (path of Sun and Moon) to form imaginary planes (like a floor on which the Moon and Sun roll around the Earth) with the Earth at the center. The Moon’s plane is slightly tilted at an angle of 5 degrees with respect the Sun’s plane. Such planes would intersect at two points in the sky and we call them Lunar Nodes in astronomy. In Indian astronomy, these points were identified as ‘Rahu and Ketu’.

The tilt between the two planes causes the Sun-Earth-Moon system to be slightly out of alignment and therefore prevents Eclipses from occurring every month. However, when the Moon achieves the Full-Phase at one of these points, the Sun-Earth-Moon alignment is almost straight and therefore, the Moon passes through the Earth’s shadow causing a Lunar Eclipse.

What is Penumbral Eclipse?

This eclipse occurs as the Moon passes through Earth’s penumbral shadow. The penumbral shadow is a part of the shadow of any object. The darkest region of the shadow of any object is called the Umbra and the light, blurry outer edge of the shadow is called the Penumbra. When the Moon passes only through the Earth’s penumbra, we call it a Penumbral Lunar Eclipse and when the Moon passes partially through Earth’s Umbra, we call it a Partial Lunar Eclipse. If the Moon completely passes through the Earth’s Umbra, it turns red and is called a Total Lunar Eclipse.

Penumbral eclipses are hard to notice, as the Earth’s penumbral shadow is faint and the reduction in the brightness of the Moon at peak eclipse will be very less. For an untrained eye, the peak eclipse might look like a normal full moon with a slightly reduced brightness.