Total Lunar Eclipse - 27 July 2018

A Total Lunar Eclipse is very easy to enjoy, you just have to go outside and look at it!

Find a good location beforehand, maybe a couple of days prior to 27 July, where you can have a clear unobstructed view of the sky. The Moon will be high in the sky when it enters the umbra but will be near the western horizon near the end of the eclipse. Make sure that there are no very bright lights nearby, so that the fully eclipsed Moon will be beautiful and bright. If you are hosting a public event, you may want to ensure that there is plenty of space for people to move around safely.

Though it will be cloudy from most parts of India, you can still enjoy the eclipse if the clouds are in motion, with periods of clear skies, or even if there is a very thin cloud cover. So do go out and check every once in a while throughout the night.

Just follow the Moon as it gets eclipsed in the sky. The penumbral eclipse will not be spectacular, and you may not even be able to see a difference unless you look carefully. However, the umbral eclipse is obvious, where you can see the circular shadow of the Earth progressively cover the Moon.

If you have a small telescope or a pair of binoculars, the partially eclipsed Moon will look beautiful through it. Make sure that you have a long focal length eyepiece so that the entire disk of the Moon can be seen in the field of view.

Yes! It is absolutely okay to see the eclipse, and share the joy of the event with people you know.

We need to take precautions while seeing a solar eclipse. Any accidental viewing of the uneclipsed part of the Sun, especially through a telescope, can permanently damage the eyes. Even so, hundreds of millions of people regularly see solar eclipses safely using solar filters and other devices. There is no such danger for a lunar eclipse - after all, we can all look at the un-eclipsed full Moon without any problem!

You may hear that one should stay indoors and not eat during an eclipse, etc. These kinds of beliefs are common around the world have no basis in science. They come from an age when humans did not understand the sky and were easily frightened by eclipses. We would do well to follow the great astronomer Aryabhata (476-550 C.E.) who gave the correct explanation of eclipses as well as a method to calculate them, and did not believe in any of the myths surrounding these events. For further reading on Aryabhata, eclipses, and myths versus science, read this article

So, you can see the eclipse with your naked eyes or using a telescope and you can eat during the eclipse. In short, there are no harmful effects from seeing the eclipse on 27 July. An eclipse is one of the most grand and awe-inspiring spectacles that nature has to offer us. Why would we not want to see it?

The Total Lunar Eclipse on 27 July 2018 will be the longest this century. Specifically, the duration of totality, when the Moon is completely inside the umbra of the Earth's shadow, is the longest this century (reckoned from 2001 to 2100). This duration is 104 minutes long. This is due to two reasons.

First, the size of the Earth's umbral shadow at the distance of the Moon, during Full Moon, is more than 2.5 times the size of the Moon itself. Hence, depending on the particular path that the Moon takes during an eclipse, it can pass at different distances from the centre of the umbra. It is easy to convince ourselves that closer to the umbral shadow the Moon passes, longer is its path inside the umbra, and longer is the eclipse.

Second, the orbit of the Moon around the Earth is not a perfect circle, but is an ellipse. This means that the distance between us and the Moon varies along its orbit, from as close as 3,62,600 km (perigee) to as far as 4,05,400 km (apogee). This means that the size of the Moon in the sky also varies along its orbit. If an eclipse occurs when the Moon is farther from us, its angular size will be less, and hence will take longer to pass across our umbra, leading to a longer eclipse.

Now, the eclipse on 27 July 2018 occurs near apogee and in addition, the Moon passes extremely close to the umbral centre. These two factors make this eclipse longer than usual. However, it is not much longer than other total lunar eclipses this century. Its duration of 104 mins is close to that of 15 June 2011 (100 mins), 26 June 2029 (102 mins) or 7 Aug 2036 (96 mins).

(Pic from here)

Did you know that the blue colour of the sky and the reddish rise and set of the Sun and the Moon are connected? Sunlight has all colours in it, but the molecules and dust in our atmosphere scatters the bluer light more than it does the red. Hence, the sky is blue all over. The light from the Sun and the Moon travelling though a long path in our atmosphere at rise and set time, is thus reddened.

During a Total Lunar Eclipse, the Earth blocks sunlight from reaching the Moon directly. However, the red light from the sunrises and sunsets can pass through the edges of the Earth, and can refract on to the Moon, making it red in colour. Hence the name, Blood Moon or Copper Moon.

For more info, see here and here.

(Pic from Stellarium)

You may notice a bright red object just south of the Moon on the night of the eclipse. This is the planet Mars!

Mars, Earth and the Sun can line up in two ways, with the Earth in the middle, or with the Sun in the middle. The former is called the Opposition of Mars, and this is when the distance between Mars and Earth is the smallest. Hence, oppositions are when Mars appears biggest and brightest. Such an opposition occurs, coincidentally, on 27 July, during the eclipse. Since a lunar eclipse also occurs when the Earth is almost exactly in between the Moon and the Sun, we can see Mars and the Moon very close together on this night. A very red Mars will be only 6 degrees south of a very red eclipsed Moon, as can be seen in the image above!

Mars will actually be closest to us since 15 years on 31 July, four days after opposition. This curious fact is because the orbits of Mars and Earth around the Sun are ellipses, and not perfect circles. This is the reason for this difference of 4 days. In addition, this ellipticity, along with the non-zero angle between the two orbits, also ensure that the distance between Mars and Earth is not exactly the same every opposition. This is why 27 July is special!