Brought to you by Dr. Roy Gretton, Journal Editor of The Nottingham Astronomical Society.
Contact details are on the Nottingham Astronomy website: https://nottinghamastro.org.uk/
Please note, the NAS new permanent venue for our main meetings on first Thursday of the month is ยญNottingham Emmanuel School, Gresham Road, West Bridgford, Nottingham. NG2 7YF
Mercury, the Elusive Planet
Some people have a bucket list of things they wish to see before they die. I have a suggestion for an item you could place on your list, and you wonโt need to travel far to see it. I refer to the planet Mercury. It is said that even the great Copernicus, the man who overthrew the ancient idea that the Sun, Moon and planets revolve around the Earth, never actually saw Mercury for himself. Of course, the object Iโm inviting you to search for wonโt appear anything like as spectacular as the Grand Canyon or the Niagara Falls. It will be little more than a speck of light unless you have a telescope or binoculars handy. But it can be seen with the naked eye, if you know where to look. What you will de๏ฌnitely need is the sky to be clear near the horizon, either in the west in the evening, or the east in the morning, with obstacles such as trees or buildings well out of the way. Such an opportunity will occur this spring, lasting from midยญ-March until the beginning of April, when Mercury will be visible in the western sky after sunset. Mercury can be one of the brightest of the planets, but is challenging to observe because it is too close to the Sun to be seen in a dark sky, which is the main reason why so few people have ever spotted it.
Mercury is a small world (about 3000 miles across) compared with Earth (8000 miles across). One of Jupiterโs moons, Ganymede, is actually larger than Mercury. Being the closest planet to the Sun, we would expect Mercury to be hot โ and indeed it is on the side facing the Sun, where the temperature can exceed 400C; while on the opposite side the temperature can fall to minus 170 degrees. This huge difference is down to the fact that Mercury has virtually no air to carry the warmth around the planet. A curious fact to get your head around is that on Mercury a day lasts longer than a year! An average โdayโ on Mercury lasts 176 earthยญ-days, while a โyearโ lasts 88 earthยญ-days. This comes about because for every three rotations on its axis, Mercury travels around the Sun exactly twice. Another curiosity of Mercuryโs orbit is that it is the least circular of any planet in the Solar System, carrying it within 29 million miles of the Sun at its closest, and out to 43 million miles at the most distant.
Although Mercury is one of the nearer planets to Earth, only three space probes have actually visited it. This is because, paradoxically, travelling to Mercury requires more energy than is needed to escape right out of the Solar System. On leaving Earth, a spacecraft trying to get directly to Mercury would be rapidly accelerated by the Sunโs gravitational pull, and would end up travelling far too fast to enter into orbit around the planet without using an impossible amount of fuel to slow it down. So a roundabout route has to be devised. It wasnโt until 2011 that a spacecraft was successfully placed in Mercury orbit, and it took nearly seven years to get there. Messenger was launched in 2004, did a ๏ฌy past of Earth in 2005, two of Venus in 2006 and 2007, and three ๏ฌy pasts of Mercury itself in 2008ยญ-2009 before ๏ฌnally going into orbit around the planet in March 2011. Now a mission called BepiยญColombo is currently on its way to Mercury, and is scheduled to go into orbit around the planet in 2025 after doing no fewer than six ๏ฌy pasts of Mercury itself.
The Planets in March and April
Jupiter will be ending its current apparition this spring. At the beginning of March it sets at 9pm but by the end of April will be setting only a matter of minutes after the Sun and will therefore be lost from view. Saturn remains too close to the Sun in the morning sky to be observed. Mars rises less than an hour before the Sun throughout March and April, and must also be regarded as unobservable. Venus, after putting in a brilliant performance over the autumn and winter months, has also disappeared from the morning sky. So, once Mercury disappears from the evening sky in April, the planets can reasonably be described as a dead loss until later in the year!
Phases of the Moon
| MAR | APR | |
| Last Quarter | 3rd | 2nd |
| New Moon | 10th | 8th |
| First Quarter | 17th | 16th |
| Full Moon | 25th | 23rd |
