By John Pressly, Science Curator & Observatory Officer at Coats Observatory
Someone once said “Men are from Mars and Women from Venus.” Whilst there are times that we may seem like different alien species to each other, the two forenamed planets are certainly vastly different in nature. This month it is possible to get a close-up view of these two celestial bodies by visiting Coats Observatory.
Throughout February, Venus and Mars will appear very close together in the sky, something referred to as a ‘planetary conjunction’. Even though these planets orbit the Sun millions of miles apart they will appear almost side-by-side in the night sky from our perspective here on Earth.
The brighter of the two is Venus, easily spotted in the early evening sky as it shines with a very bright solid light. The reason for this brightness is a thick blanket of cloud which shrouds the entire planet, reflecting most of the sunlight Venus receives back into space. The sunlight that does penetrate the clouds ends up trapped and cannot escape, thus heating the surface to an incredible 450oC, the hottest surface temperature of any object in our Solar System. The thick carbon dioxide atmosphere makes the air pressure much greater than here on Earth. In fact the surface pressure is 90 times that of our home-world, meaning if you could stand on Venus it would be like standing on the seabed with over a mile of water above you!
Aside from the inhospitable atmosphere Venus shows traces of a past volcanic history and extinct volcanoes and solidified lava flows dot the surface. It is possible that some of these may still be active as recent missions to Venus have seen evidence, such as lightning in the upper atmosphere, which may have been caused by volcanic eruptions.
To add to all the strangeness Venus also rotates in the opposite direction to all of the other planets, meaning if you could see the Venus through the thick clouds it would rise in the west and set in the east. This rotation is also very slow – it takes Venus 243 Earth days to spin on its axis once. A year on Venus is the equivalent of 224 Earth days, meaning a day is longer than a year.
Venus was radar-mapped by the NASA spacecraft Magellan in the 1990s and all of the surface features discovered have been given women’s names, either real or mythical, with one exception. The ‘Maxwell Mountains’ are named after Scottish scientist James Clerk Maxwell, meaning there is one lonely Scotsman on the planet surrounded by women!
In contrast Mars is a much colder but slightly wetter planet. Mars does have a lot of water locked up in the polar ice caps and as ice underneath the surface but none flowing openly, although there is plenty of evidence that it did so in the past. Spacecraft orbiting the planet have returned images of ancient dried-up rivers and the robotic rovers travelling across the surface have found rocks and minerals that form in water here on Earth.
Mars atmosphere is mostly carbon dioxide, similar to that of Venus but much thinner – in fact Mars’ atmospheric pressure is only about 1% that of Earth’s. The thin atmosphere means that temperatures can range from 35oC at the equator in summer to -143oC at the poles in winter.
Mars’ atmosphere is also quite dusty and planet-wide sandstorms are common, which can obscure all the surface features. Mars does have some very interesting landscapes such as the largest canyon in the Solar System, Valles Marineris or Mariner Valley, which is over 4000km long is almost 10 times longer than the Grand Canyon in Arizona in the USA.
A giant extinct volcano known as Olympus Mons towers 26km above the Martian surface, making it the largest mountain in the Solar System – if it was here on Earth it would be three times taller than Mount Everest!
The best way to see these two amazing worlds up close is through a powerful telescope such as those housed at Coats Observatory. On Tuesday and Thursday nights throughout February both Mars and Venus will be the main observing targets when the skies are clear. The observatory is open on these evenings from 6:30pm to 9pm (last entry to the building 8:45pm), admission free and no need to book. If the weather prevents telescope use planetarium shows and films will run instead.
For more information about Coats Observatory click here.