By Chaitram Aklu – FRGS
The first day of winter in the Northern Hemisphere is Monday December 21, the Winter Solstice when the sun stands still at 5:02 AM initiating the hemisphere’s longest night and shortest day. It is not however the coldest day of the year. Following the solstice the hemisphere will begin experiencing increasing daylight.
This 2020 Northern Hemisphere Winter Solstice coincides with a special and exciting event for astronomers and others interested in the heavenly bodies and the night sky. A rare alignment and conjunction of Jupiter and Saturn, two of the largest planets will look like one double planet just after sunset on December 21. They will appear to touch, thereby giving the impression of a huge extremely bright star. This rare event can actually be seen from earth – a sight that was not possible for 800 years because it rarely happens this close to earth. It must be noted that while from earth the planets will appear close, they are not in the same orbit and are far from being close. In fact they are more than 400 million miles apart.
According to scientists the last time observation was possible was March 4, 1226. Jupiter, the fifth planet from the sun, is larger than all the other planets and their moons combined. Saturn, known as the ringed planet, is the sixth planet from the sun and has over 250 000 miles of rings. It is also the third brightest planet in the night sky. This conjunction has already been dubbed the Christmas Star because of its occurrence so close to Christmas Day.
Why is the event so exciting? I asked Patrick M. Hartigan Professor of Physics and Astronomy at Rice University in Houston Texas. “It’s pretty, it’s rare, and it’s fairly easy to see. It won’t look like a brilliant star. There will be a fairly bright object in the dusk sky, up about 10-15 degrees for you, with a much fainter object just to its right. If you have a lot of light pollution a pair of binoculars will help. But you need to go somewhere you can watch the sun set without a lot of trees or buildings around. After about a half hour it will get dark enough to see Jupiter and Saturn will be right next to it, but 10 times fainter.” He told me in an email.
And why is the occurrence so rare? “Saturn and Jupiter move slowly, so once they line up it takes 20 years for Jupiter to loop around the sky and catch up with Saturn again.” He said. And to my question: Are there any more significant events soon? “They happen regularly every 20 years, but some appear too close to the sun to observe, and most are significantly wider than ours. The planets haven’t appeared this close together in the sky since 1623, and that one was too close to the sun to see. The last time such a close conjunction between these two planets was observable was in the dawn skies in March of the year 1226.” Hartigan told me.
On the solstices, places in the hemisphere experience the shortest period of daylight and the longest period of darkness of the year. (Monday, December 21 in the Northern Hemisphere and Saturday, June 20 in the Southern Hemisphere) It should be pointed out however that while the solstice marks the shortest period of daylight, it is not a case in which the sun rises latest or sets the earliest.
It is possible to observe the conjunction around the world on December 21. However observers close to the equator have the best chance and are encouraged to start looking until Christmas Day (15 -20 minutes after dark) to identify the planets and track them. The two planets will not just appear suddenly as a star on December 21. If you are on the lookout at the opportune time you will see the conjunction with your naked eye but using a telescope and a vantage position will definitely be to your advantage.
According to NASA, you can use a cell phone camera to record the event. One with ‘night mode’ and wide-angle lens features will enhance your photos. But remember on December 21, the day of the Great Conjunction the planets may look merged. To show the sequence it would be better to photograph before, on and after December 21.