An incredibly rare event will occur on this January 31. The end of the month will see a lunar eclipse happen during a blue moon. A lunar eclipse occurs when the earth moves in front of the moon, in between the sun and the moon. This casts a shadow on the moon. Meanwhile, a blue moon refers to the second full moon which occurs in a month. These two events will happen on the same night, making it a rare event that hasn’t happened for the last 150 years.
The last blue moon lunar eclipse occurred back in March 1866, almost 152 years ago. This makes blue moon lunar eclipses fairly rare events, though fortunately a bit of luck has ensured that we are around for this eclipse. Furthermore, those who miss the lunar eclipse this year may have another chance to see one on December 31, 2028, and then again on January 31, 2037.
What’s A Blue Moon?
Technically, there are two different definitions of a blue moon. A much older version of the term refers to the third full moon that happens in a season which has four full moons. This is sometimes referred to as a seasonal blue moon, and this event occurs approximately every 2 ½ years. The more familiar use of the term blue moon refers to the second full moon within a month, the monthly blue moon came out of a misinterpretation of a definition included in a Farmer’s Almanac.
Note that the moon does not actually appear blue in the sky. It remains the same color. Though rare events actually can cause the moon to appear blue, such as dust within the atmosphere after a fire or dust storm. This can also occur after volcanic eruptions such as the eruption of Krakatoa in 1883 or Mt. Saint Helens in 1980.
How Does A Lunar Eclipse Happen?
Everyone knows that the moon has phases, but a lunar eclipse can actually only occur during a full moon. Furthermore, the moon must pass through some part of the Earth’s shadow. The shadow the Earth casts is split into two different parts, a penumbral region, and an umbral region. The penumbral region is the where the Earth prevents only some of the light coming from the sun from reaching the moon, still allowing some of the light to reach the moon. The umbral region is the darkest part of the shadow, where the Earth stops all the sun’s rays from reaching the moon.
Due to the interactions between the moon and the shadow cast by the earth, three different types of eclipses can occur: penumbral lunar eclipse, partial lunar eclipse, and total lunar eclipse.
In a penumbral lunar eclipse, the moon will pass only through the penumbral portion of the Earth’s shadow. These typically aren’t very visually impressive, and they are also hard to observe. Partial lunar eclipses occur when only one part of the moon passes through the umbral shadow cast by the Earth. These events are easy to see, even with the unaided eye, though they are not quite as impressive as total lunar eclipses. For a total lunar eclipse to occur, the entire moon must pass through the umbral region of the Earth’s shadow. The moon often turns a sharp red color during the phase of totality.
If you’re curious as to why the moon does not experience an eclipse every month during a full moon, this is because the orbit of the moon around the Earth is off-center, when compared to the Earth’s orbit around the sun. The moon orbits the Earth approximately 5° below or above the Earth’s plane of orbit around the sun, meaning that the moon is typically out of the zone of shadow when it is on the far side of the Earth. Slight fluctuations in the moon’s orbit mean that approximately 2 to 4 times every year, the moon will pass through part of the Earth’s shadow causing one of the three types of lunar eclipses.
Why Does The Moon Look Red?
As for why the moon turns red during a total lunar eclipse, it is because of the sunlight passing through the Earth’s atmosphere. Even though the moon is completely within the Earth’s shadow, rays of light from the sun can still indirectly illuminate the moon. This occurs because the Earth’s atmosphere is refracting and bending some of the light from the sun, allowing these rays of light to reach the moon. Because these rays of light are going through the Earth’s atmosphere, the atmosphere filters out most of the blue colored light. As such, only light within the red and orange wavelengths can hit the moon and illuminate it. This causes the moon’s general red/orange appearance during a total lunar eclipse. The precise color the moon turns to an observer varies, depending on their location on the Earth and what sort of atmosphere they are looking at the moon through.
Naturally, where you live will affect when and how much of the blue moon lunar eclipse you will be able to see. If you live somewhere on the West Coast of the United States, the phase of totality will begin around 4:51 AM Pacific Standard Time. Unfortunately for those on the East Coast, they will only be able to see a partial eclipse before the moon dips below the horizon. The moon will be entering the umbra, which is the darkest part of the Earth’s shadow, around 6:50 AM Eastern Standard Time, just as it is sinking below the horizon.
The best places to see the eclipse (in the USA) will actually be in Alaska and Hawaii, as these regions will get to see the majority of the eclipse. The Pacific Ocean will be facing the moon for most of the eclipse, so those who live in places like Australia, New Zealand, both Central and Eastern Asia, as well as Indonesia, will have an excellent view of the event.
Meanwhile, those who live in Eastern Europe and the Middle East will have to contend with only seeing part of the eclipse, as the eclipse will already be occurring as the moon rises in these regions.
Be sure to check when the lunar eclipse will be visible in your area on the 31st. You won’t want to miss the event, if at all possible.