Rishiraj Bhagawati Jul 28, 2018 20:03 PM IST
With the longest total lunar eclipse of the 21st century scheduled for 27 July – and other celestial spectacles also lined up this month – stargazers have a busy calendar in the coming weeks. But given the time of the year, will monsoon play spoilsport? Experts believe clear skies are unlikely over most of India, although they would love to be proved wrong this one time.
The lunar eclipse, which will last one hour and 43 minutes, will also feature a "Blood Moon" — which is a non-scientific term used to refer to the red tinge on a fully eclipsed Moon. It will be preceded and followed by partial eclipses lasting over an hour.
The eclipse will be visible in parts of South America, most of Africa, and West and Central Asia. For viewers in India, the eclipse, both partial and the total, will be visible in their entirety from all parts of the country. The partial eclipse of the Moon will start around 11.54 pm IST, with the total eclipse beginning at 1 am on 28 July.
"The greatest eclipse, when the moon will look the darkest, will be at around 1.52 am and the totality will continue until 2.43 am. After this period, the moon will remain partially eclipsed till 3.49 am of 28 July," Debiprosad Duari, director at MP Birla Planetarium in Kolkata, said.
But will this timing pose a problem for astronomy enthusiasts? The director of the Mumbai planetarium thinks it may.
"The event is taking place close to midnight. Also, this being the monsoon season, travelling all the way to the planetarium at midnight to look at the eclipse might not be convenient for people. Since the eclipse is visible from anywhere, no matter where one is located, I am not inclined to keep a public viewing for the eclipse at this point of time. However, we will attempt to webcast the event if the sky clears up a little bit," Arvind Paranjpye, director of the Nehru Planetarium in Mumbai, told Firstpost.
Those final words of Paranjpye have some stargazers worried – will the skies clear up in time? Paranjpye says it is impossible to say for sure, but one shouldn't be too pessimistic either. "We really cannot predict one way or the other."
"If you want to be absolutely assured of having a clear view of the lunar eclipse, you will have to go 10 kilometres above the atmosphere, anywhere in India. That is the safest bet," Paranjpye quipped, as he recalled a two-decade-old incident.
"I remember one particular total solar eclipse of 1999. A small group of amateur astronomers from Nagpur decided to go somewhere far away to see the event, and the sky cleared up above the area over them just at the right time. Everywhere else in the country, people couldn’t watch the eclipse, even at places that were known to have clear skies. So it is often a matter of luck."
Something else that can turn out to be a matter of luck is the visibility of Mars on the same day. The Red Planet will come closest to Earth in 15 years during the total lunar eclipse.
On 27 July, Mars will be opposite the Sun in Earth's sky, just 51 days before it passes through perihelion, which is its closest point relative to the Sun in its orbit. As a result, the minimum distance between Mars and Earth will shrink to about 57.58 million kilometres on 30 July.
On that day, Mars will shine brightly, which means that it will blaze twice as bright as Jupiter, but dimmer than Venus. In other terms, the Red Planet will easily be visible to the unaided eye under a clear sky – the last part again being the most important.
Late at night on 27 July, the full moon will be near its apogee – the farthest point from Earth in its orbit around Earth – and it will be the smallest full moon of the year.
"This smaller and slower-moving full moon takes more time to cross the Earth's shadow than does a full moon that's closer to Earth and moving faster in orbit. That is why a full moon at or near lunar apogee adds to the duration of a total lunar eclipse," Duari said.
The full moon will plunge deeply into the Earth's shadow on the night of 27-28 July and the Earth-Moon distance just before the eclipse will be around 4,06,223 kilometres. The longest possible total lunar eclipse is 1 hour and 47 minutes. In this case, the centre of the lunar disk aligns almost perfectly with the centre of the Earth's shadow.
During a total lunar eclipse, the moon's disk can take on a dramatically colourful appearance from bright orange to blood red, and sometimes dark brown to very dark grey depending upon the part of the Earth's shadow it will be passing through.
With inputs from agencies