The National Aeronautics and Space Administration’s (NASA’s) prediction is correct, and we will be able see a super blue blood moon in the night skies today on January 31st, 2018. In this event the lunar eclipse with a reddish moon, the super moon (a closer and larger moon) and the blue moon (two full moons within a month) could all be visible simultaneously. Termed as a super blue blood moon, this sort of lunar eclipse is an extremely rare event and last occurred in December, 1982. It is expected to happen again only in 2037, if predictions hold (Petro, 2018).
A lunar eclipse occurs when the Sun, the Earth and the moon are aligned in a straight path where the Earth is positioned between the Sun and the moon such that the Earth blocks sunlight for the moon. In the process of sunlight being completely blocked by the Earth in a total lunar eclipse, the moon can for some observers on Earth, appear with a reddish hue due to the manner of the scattering of blue light by the Earth’s atmosphere where parts of sunlight belonging to reddish wavelengths reflect off the moon, caused also partially by Earth’s shadow during a lunar eclipse. This sort of reddish moon is called a blood moon.
This produces an optical effect similar to how we see iridescent clouds or reddish sunsets due to the scattering of the visible colour spectrum of sunlight by the Earth’s atmosphere. Iridescent clouds are rainbow coloured clouds seen due to the optical effect produced by the diffraction of sunlight by water droplets or tiny crystals in the clouds. Similarly, a reddish sunset occurs because of the refraction of sunlight by its passage through a greater depth of the Earth’s atmosphere, such that shorter wavelengths in the colour spectrum are rendered invisible and the Sun appears reddish due to the longer wavelengths of reddish hues.
Fig: NASA’s predicted mapping of the global visibility of the lunar eclipse
Although the next lunar eclipses are predicted for July 27th, 2018, and January 21st, 2019, they will not be blue moons (NASA, 2018). A blue moon happens when a full moon appears twice in a month, giving rise to the adage of ‘once in a blue moon’. The moon will n0ot be blue in hue and blue moon is merely a term. The moon’s orbit around Earth is also not completely symmetrical as an equidistant circle. At its farthest from the Earth in the moon’s orbit it is termed as apogee, and at its nearest to the Earth it is termed as perigee, when the moon appears fairly larger and brighter to observers on Earth. In a perigee, the moon appears about 14 per cent bigger and 30 per cent brighter to observers on Earth. Although the changes in the moon’s visible size might not be perceptible for most observers, the optical effect is most pronounced when one catches a full moon as it rises or sets (Science at NASA, 2017). However, it will not be until 2037, as mentioned before, that these three phenomena occurring simultaneously will produce a super blue blood moon.
People who live in northwestern US, Canada, in Australia, New Zealand and eastern Asia will be able to view the entire event (Lewin, 2018). In India people in India’s northeastern states will be the first to view the event between 4:21 and 5:18 pm IST. The west coast of India and Rajasthan will be able to see the event between 6:21 to 7:37 pm IST (Bhattacharya, 2018). People in Delhi can see the event between 5:53 to 9:38 pm IST and the effects are predicted to be maximum at 18:59 pm IST.
Noah Petro of NASA speaking with Sarah Lewin of the astrophysics website Space says that researchers can be interested in the cooling of the moon that happens during the total lunar eclipse. The cooling of the moon during a total lunar eclipse is much more sudden than in the Earth during a solar eclipse because of the absence of an atmosphere on the moon. This cooling of the lunar surface, Petro says, can help us in understanding the properties of the lunar surface better which cannot be properly understood in the normal day/night cycle of heating of the lunar surface, particularly parts of the lunar surface that are inaccessible to astronauts (Lewin, 2018).
NASA however, is experiencing some problems in studying the lunar surface during the eclipse in that its Lunar Reconnaissance Orbiter (LRO), which draws its power from sunlight, will be shut down for the duration of the eclipse. Although the LRO can shift to batteries during a lunar eclipse, the extreme cold has strained the orbiter which has been through 7 lunar eclipses since its launch in 2009. As a solution NASA has said that all instruments on board the LRO will be shut except for the diviner, which can study how the uppermost portion of the lunar surface responds from hot temperatures to quickly advancing extremely cold temperatures during the lunar eclipse. The diviner has been used in lunar eclipses before and can help in establishing time scales on the behaviour of the lunar surface (Johnson, 2018).