Finding NGC 457

NGC457: The Owl Cluster (or E.T. Cluster)

NGC 457
The Owl Cluster; The E.T. Cluster
Open Cluster
Season Visible in Evening
Summer & Autumn; Aug – Dec
Conversation Notes
Open Cluster. Would be unremarkable except for the shape, and two bright stars, that make it look like various amusing objects.

This isn’t a particularly dense or interesting open cluster. It’s in the beginner’s repertoire because of an amusing coincidence: it has two bright stars positioned so that the human observer tends to think, “eyes!”, and then your mind will easily fill in the rest of the shape of an animal. The traditional interpretation was of an owl but, in the last 20 years or so, people have found it easy to imagine the movie character “E.T.: The Extraterrestrial” in the cluster.

Kids who have the seen the movie, and especially parents, get a great kick out of this. I’ve heard “hey, hon! come and look at E.T.” many times at star parties, and I always smile.

Open clusters are easy to find and observe in small telescopes, pretty, and scientifically important. This is a group of stars all born from a common cloud of gas and dust. Since they came from the same gas cloud they are, astronomically speaking, all about the same age and all about the same distance from us, and they all started with about the same chemical composition. Knowing that they are the same age and at the same distance, the fact that they have different appearances allows us to learn a great deal about stellar evolution – the different appearances can only be a result of the different masses of the different stars.

Finding NGC457

Find the constellation Cassiopeia. It’s shaped like a W, and is found on the other side of Polaris from the Big Dipper. It rotates around the sky with the seasons, so it may be upside down or on its end.
Let’s have a closer look at Cassiopeia, oriented as it would be on an August night.

We’ll name a few of Cassiopeia’s stars for easy reference.

”Gamma Casiopeiae ”is the centre star of the “W”. (It is sometimes informally called “Navi”. This name, which is “Ivan” backwards, was given to it by astronaut Virgil Ivan (Gus) Grissom.) Then heading out toward the lopsided end, we pass ”Ruchbah” and end at ”Segin”.

Imagine extending the line from Segin to Ruchbah farther, so it sticks out into the space below the centre of the “W”.

Extend that line just far enough that a line dropped down from Gamma would meet it at a 90 degree angle.

For observers old enough to have taken technical drawing in school, it forms a nice 30-60-90 triangle.

Point your telescope below the corner of this triangle, at a distance about 1/2 the length of the short side of the triangle.
The cluster is quite small, and the stars are dim except for the “eyes”. In a 6×30 or 8×50 magnifying finder, you will probably see only the “eyes” – two stars very close together. Centre these.

In your main telescope, select an eyepiece that will give 30x to 50x magnification. This view is about 30x.

Find the two bright stars for eyes, then look for the body and arms. The image may be upside down or on its side.

Here I’ve rotated the image so the eyes are on top.
This cluster was traditionally called “the Owl Cluster” – the bright stars are the eyes of an owl, whose body can be seen, and who is sitting on a branch.
It’s also often called “the E.T. Cluster”, because it is easy to see E.T.’s bright eyes, plump body, and outflung arms.

All the above images were generated with Starry Night Pro.

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