The Night Sky February 2020
It sounds like a great title for a new Harry Potter book but I refer to Hydra, the largest constellation of all. Portions of it are visible from anywhere in the world. The most recognisable part of the constellation is its head; this is made up of a group of six stars. In mythology, it was the second of Hercules’s twelve labours to defeat the Hydra. The sea monster had the body of a snake with nine heads. When one was chopped off it just sprouted another 2 or 3! He managed to defeat it and the story is immortalised in the sky. Mid-month, looking south-east half-way up the night sky you will see Hydra’s head, just to the right of the inverted question mark that forms Leo. It is not until mid-March around midnight that the whole constellation becomes visible in its entirety. Located in the constellation of Hydra is an object that William Herschel discovered in 1785 and it is mysteriously named the ‘Ghost of Jupiter’. This object is a star that has thrown off its outer layer to produce a wonderful display called a planetary nebula. It is very faint, but at the centre is the remnant white dwarf star.
To look at it through a telescope, you will be reminded of the similar appearance and apparent size to the planet Jupiter, hence the name. Of course the nebula is much further away (1000 light years) so as you can imagine it is colossal, at 2 light years across!
Exoplanets
Back in 1991 we only knew of one solar system, ours! We looked out into space and only guessed that they existed elsewhere. No-one could have imagined that by 2020 that we would have discovered over 4000. What is even more remarkable is the way they are being discovered.
The transit method is measuring a small dip in the light of a star as an exoplanet passes in front. Another method is by detecting the ‘tug’ the planet makes on its parent star by measuring how this effects the star’s distance to us. Both of these methods are amazing in the sense that the measurements are so miniscule. It is also a demonstration of how ingenious astronomers can be in discovering something that seems impossible to do.
Exoplanets range in size and positions. Some are more massive than our own Jupiter, others are smaller than Earth. The orbits range from the parent star to very distant to incredibly close. Importantly, the range of distances from the parent sun where liquid water could exist on a rocky planet is called the habitable zone. Latest research shows that nearly a quarter of Sun-like stars have Earth-sized planets in their habitable zones. There has even been an exoplanet discovered that has its own exomoon!
So when you look out into the dark night sky this month, just pick any star and in all likelihood it will have planets orbiting it. You may pick one that has a planet in the habitable zone. The question it raises is how common is life out there?
Moon and planets this month.
The Full Moon this month is on 7th February (New Moon 23rd).
Between 18th-20th of this month you will get the chance to see Saturn, Jupiter and Mars just before sunrise, very low in the south-east. They will appear to be following the same path of the Moon over this period.
A very bright and brilliant Venus will be on show in the evening sky towards the end of the month looking West.
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