Eclipses represent one of the more fascinating spectacles in astronomy, occurring either when the moon enters the Earth’s shadow – a lunar eclipse, during the full moon phase, or when the Earth pass through the moon’s shadow – a solar eclipse, during the new moon phase. The difference in size between the Earth and the moon, and thus the difference in their shadow widths, coupled with the relative distances and sizes of the moon and the sun as seen from Earth, mould our experience of both eclipse types.

In understanding eclipses, it is important to understand that the Earth and the moon are not always perfectly in line with the sun. The moon’s orbit is tilted by around five degrees from the plane of the Earth’s orbit around the sun, meaning that the moon is only fleetingly exactly in the same plane as Earth and the sun. When it is, however, it lasts long enough in that plane – between 31 and 37 days – for there to always be two eclipses – one lunar and one solar – a fortnight apart, and possibly three eclipses in a month, if the timing is just right. This period of 31-37 days is called the eclipse season, and happens approximately once every 173 days.

Solar eclipses involve the Earth’s passage through the moon’s shadow, with the umbra – the darkest part of the shadow – only covering a small portion of the Earth’s surface. As a result, in the event that the moon’s umbra does cross the Earth’s surface during a total solar eclipse, only a small portion of the planet gets to experience totality, with most observers in other locations experiencing partial eclipses of varying percentage coverages, depending on distances from the path of the lunar umbra.

The occurrence of solar eclipses is further complicated by the fact that the distance between the Earth and the moon varies, roughly between 350,000km and 410,000km

The occurrence of solar eclipses is further complicated by the fact that the distance between the Earth and the moon varies, roughly between 350,000km and 410,000km. If the moon happens to be further than around 384,400km during a solar eclipse, its angular size in the sky is not enough to completely cover the sun, and thus an annular eclipse occurs instead. In this case, the Earth would be passing through the moon’s antumbra, as opposed to the umbra.

Lunar eclipses, on the other hand, involve the moon’s passage through the Earth’s shadow. In the event that the moon completely passes through Earth’s umbra, the entire lunar surface is covered by Earth’s shadow and this can last for a total of nearly two hours.

Anywhere on Earth where the moon would be visible in the sky at the time would be able to experience the lunar eclipse. A partial lunar eclipse would be one where the moon only partially enters the Earth’s umbra, but this would once again be visible from anywhere on Earth where the moon is visible in the sky.

We are indeed currently in an eclipse season – with a partial lunar eclipse having occurred (locally) in the early morning hours of last Wednesday. Sure enough, it is also one of a pair of eclipses in this eclipse season – it will be followed by an annular solar eclipse on October 2, which will unfortunately not be visible from Malta.

Josef Borg completed a PhD in astronomy at the Institute of Space Sciences and Astronomy, University of Malta, and is currently a post-doctoral researcher in space biology and astrobiology at the Faculty of Health Sciences at the University of Malta.

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DID YOU KNOW?

•         Caution is required when observing a total solar eclipse. Experiencing a total solar eclipse first hand is an experience like no other but requires caution to ensure eye safety. The moments leading up to totality and just after totality can be hazardous to observers. Never observe the sun through any optical instrument, be it a camera lens, telescope, binoculars or any other such device, without the appropriate solar filters in place!

•         Malta will almost experience a total solar eclipse in 2027. On August 2, 2027, Malta will experience a 97.33 per cent partial solar eclipse, with totality being visible over the Arabian peninsula, Northern Africa and Gibraltar. The next total solar eclipse actually visible in Malta will occur in 2088!