At this time of year the familiar sight of the Pleaides rising means that Winter’s on its way. They’re easy to observe with the naked eye or whatever optical instrument you have, but can be a little tricky to image.
M45 – the 45th object in Messier’s catalogue, also known as the Pleiades or the Seven Sisters, are easy to find and visible with the naked eye. They are one of the best objects to wow your family and friends with through a telescope! To find them, follow the 3 stars of the belt of Orion up to the right to reach Aldebaran, the red eye of the bull in Taurus. Continue the line on a little further and you reach the Pleaides.
Most people can see 5, 6 or 7 stars with the naked eye but there are many more visible through binoculars or a telescope. In reality, there are probably over 1,000 stars associated with the cluster. Galileo Galilei was probably the first astronomer to view the Pleaides through a telescope and he reported on it in 1610.
M45 is an Open Cluster containing mostly hot B-type stars (very luminous and blue-ish!) and lies 444 light years from Earth. Images show a blue reflection nebula around the cluster. It’s likely that this is not actually associated with the cluster but simply a gas cloud that the cluster is curently passing through.
There are several reasons why the cluster can be tricky to image well:
- It’s a large cluster – about 110 arc minutes across (almost 4x the size of the Moon in the sky) and so it can be difficult to fit into your telescope-camera combination’s field of view.
- The main stars are bright – so with longer exposures the brighter stars can burn out and overpower the image, even causing stray reflections in the optical system.
- The nebulosity is faint compared to the stars – so if you expose long enough to show the nebulosity, stars can get overbright and bloated in the image.
It’s a balancing job to get imaging the Pleiades right, but when you do they are a very beautiful and rewarding subject.
Article and banner image Mark Phillips
Charts from Cartes du Ciel and Stellarium