The main highlights for this month are Orion, Mars and Saturn.
There is lots to see in Orion, which is visible around the South throughout the evening (click on the map to the left for a bigger version).
Betelgeuse (a name that is often thought to translate from 'armpit of the central one'!) is a red supergiant star, to the top left of Orion. It is so big that if the Sun were to be replaced by Betelgeuse, the outer layers of the star would lie in the asteroid belt between Mars and Jupiter. The outer layers of the star also have the density of air.
To the bottom right is Rigel, a white supergiant star about 40,000 times brighter than the Sun.
Between the two are the three belt stars of Orion. The far left star in the belt is Alnitak, and close to that star is the Horsehead nebula, unfortunately too faint to be seen with the unaided eye (nebula is a Latin word meaning cloud).
One nebula that is visible to the unaided eye is in the dagger stars that hang down from the three belt stars. Take a look through binoculars and - wow - what a sight! Even better through a small telescope. I will talk more about the Orion nebula in a follow-up posting soon.
To the top right of Orion is the constellation of Taurus, the Bull, with the bright red giant star Aldebaran forming the eye of the bull. To the top right of Aldebaran are the Pleiades - a beautiful cluster of stars that is a delight in binoculars. Don't bother looking at the Pleiades through a telescope however, unless you have a very wide angled lens, since this star cluster is far too big, being bigger than the Moon!
But what about the planets?
Well, the five main planets have all been known about since antiquity, thanks to them being so blindingly bright. Mars is especially so at the moment, due to it being on the opposite side of the Earth to the Sun. It is around the south all night - just look for the brightest red object you can find in the sky!
After admiring Mars, and if it is later than 8pm, look to your left by 90 degrees to see another bright planet, Saturn. How do you know if you've found it? Well, take a look in binoculars, and you may just be able to see the rings around Saturn - although you will need a small telescope if your eyes are older than 30.
To the top right of Saturn is the bright star Regulus, and above Saturn is the bright star Algieba - a beautiful orange-yellow double star system, well worth a look with a telescope while looking for Saturn's rings.
The Camera Obscura will be closed from 21 May until 25 May. The rest of the Royal Observatory and Meridian Line remain open.