THERE is going to be a lunar eclipse this coming Jan. 31. During the eclipse, the Moon will turn reddish-brown, leading to the use of the term ‘blood moon’ to describe such celestial events.
Where and when will you be able to see it? Why do lunar eclipses happen, and why does the Moon appear red? And what makes this next eclipse special compared to other lunar eclipses?
If you are living in the Philippines, you will be able to see the entirety of the lunar eclipse next month. Those living in the eastern parts of Asia, including Japan and many parts of China, as well as those living in Australia and the Pacific islands, will also be able to see the eclipse from start to finish.
The lunar eclipse on Jan. 31 will begin at around 6:51 p.m., Philippine Standard Time (PST). The entire eclipse will go on until midnight.
However, the Moon won’t appear to be obviously darkened until about 7:48 p.m. PST. This has something to do with the nature of shadows and eclipses, so before we go back to the times when you see the most remarkable changes in the appearance of the Moon, let us first review the science of lunar eclipses.
A lunar eclipse happens when the Moon enters the Earth’s shadow. During a lunar eclipse, the Earth is between the Sun and the Moon. The light from the Sun therefore gets blocked by the Earth from reaching the Moon.
As you can imagine from the configuration of the Earth, Moon, and Sun during a lunar eclipse, such events can take place when the Moon is either full or close to being full.
As the Moon goes around the Earth once every 27 days, the Earth’s shadow misses it most of the time. This is why we do not get a lunar eclipse every full moon.
Like everything else that cast shadows, the Earth’s shadow has two parts, a darker ‘umbra’ and a less dark ‘penumbra.’
The Earth’s penumbra is bigger than its umbra, especially at the distance of the Moon. This is why in many lunar eclipses, the Moon only enters the Earth’s bigger, not-so-dark penumbra.
During such ‘penumbral lunar eclipses,’ the Moon only turns grayish in color, as if dark ash has been thrown into the face of a regular, silvery full moon.
During the lunar eclipse this coming Jan. 31, however, the Moon is entering the Earth’s darker umbra.
The start of the coming eclipse at 6:51 p.m. is when the Moon begins entering the Earth’s penumbra. At around the time, it takes a trained eye to notice anything different with the Moon.
As the Moon moves deeper in the the Earth’s penumbra, it will appear less and less bright. By around 7:48 p.m., most people would notice a dark gray shadow touch a part of the Moon. That shadow is the Earth’s umbra.
As the night goes on, the umbra will appear to cover more of the Moon’s face. By around 8:51 p.m. Philippine time, the umbra will appear to cover the entirety of the Moon. By this time, the Moon will appear brownish-red in color, earning the name ‘blood moon.’
The Moon will appear darkest red at around 9:30 p.m. Philippine time.
The reason why the Moon turns reddish during a lunar eclipse is the same reason why sunsets on Earth appear reddish in color and why the sky looks blue.
Different colors of light get scattered differently by the atmosphere. Blue gets scattered easily, making the sky appear blue.
Red and orange get scattered least. When the Sun is setting, sunlight has to pass through a much thicker layer of atmosphere to get to the surface, by which time all the other colors have been scattered leaving red and orange to dominate.
The remaining reddish parts of sunlight that passes through the Earth’s atmosphere gets bent around the globe and goes into the Earth’s umbra. When the Moon enters the Earth’s umbra, it gets bathed in this reddish light, making it appear red.
If you have not seen a ‘blood moon’ before, you should definitely see one. If next month’s blood moon will be your first, then lucky you! This lunar eclipse also happens to be a “supermoon” or a larger than average full moon.
Because the full moon of Jan. 31 is the second full moon of the month after January 2nd’s, it will also be a “blue moon,” a term sometimes used to describe the second full moon of a month. Blue moons aren’t really blue. In fact, January 31st’s will be appear reddish.
So mark that date on your calendar and don’t miss this celestial treat!
Pecier Decierdo is the resident physicist and astronomer of The Mind Museum.
