Object: NGC 457 (Caldwell 13, ET Cluster, Owl Cluster, Number 5 is Alive! cluster)

Magnitude A / B / C
Separation A-BC/ AC
Position angle A-BC / AC
Spectral class A / B / C
Colour A / B / C
: Cassiopeia
: 01 19.5 / +58 17
: 20
: 6.4
: 204
: ? depends
: 2500-3000
Detail sketch:
Date / Time
Observing Location
Seeing / Transparency
Magnification / Field of View '
: 19/08/09 / 01:44
: Landgraaf
: 3 / 5
: Orion Optics UK 300mm
: 22mm Nagler Type 4
: 73 / 68

Observing Report

This striking open cluster is very easy to find and identify. Even with the lowest magnification possible, the 35mm Panoptic (46x and true field of view 89'), it is completely detached from the background. I first tried all possible magnifications but in the end I like the looks through the 22mm Nagler best. It shows NGC 457 nicely with some space left around it. This eyepiece was also used for the sketch.

NGC 457 looks like a little "stick-figure" with its arms spread out widely, and he welcomes me to visit his wonderful world. It looks like a very warm welcome. A nice way to start the observation! The shape of the little figure is very obvious. In my 300mm Dobson he stands right up with his feet down in the north and his head with two glittering eyes up in the south. He spreads his arms out to the east and west. A lot of observers refer to NGC 457 as the ET- or Owl cluster, and I understand why, but to me personally, NGC 457 reminds me very much of Johnny, the friendly robot from the movie "Short Circuit" (Number 5 is alive!). On the movie poster he stands with his mechanical arms stretched out to the heavens, while being struck by lightning, and that's exactly the pose I recognize in the star pattern of NGC 457.

A pair of bright stars represents the eyes of Johnny. One is definitely yellow with a hint of orange, the other looks plain white with a suspected very faint yellowish hue, but I'm not 100% sure about this. I know there is a magnitude 9 M class star somewhere in this cluster, which should be "red", though I cannot find it visually. There is no real "central star". However, I do see two small asterisms inside the "body" of NGC 457, which jump right out at me. First of all, going north from the eyes I see three stars forming a little triangle. A bit more to the north, somewhere on Johnny's chest, I see a group of six stars forming a large question mark.

There are several chains of stars forming the arms and feet, but there are also dark and empty patches. I see no glow of unresolved stars or nebulosity. It is a sparkling bright cluster but not very rich in stars. While sketching the cluster I counted about 45 to 50 stars, some of them popping in and out of view. I didn't include all of these stars in my sketch. The two bright eyes of Johnny are of magnitude 5 and 7. The other stars magnitudes range from 8 to 13, so there's quite a large range of magnitudes visible.


NGC 457 and the Cassiopeia window

When looking towards Cassiopeia, we are actually looking away from the galactic center. Our Sun is situated on the inside of our own spiral arm, so when we look away from the centre, we look into our own spiral arm, and towards the outer arms of our galaxy. In large parts of Cepheus and Perseus our view of the outer regions is blocked by nearby dust clouds. In Cassiopeia however the milky way looks much richer and better visible than in its surrounding constellations.

This is because in Cassiopeia there is a large gap in the dust clouds that block the view of the milky way in Perseus and Cepheus. This gap is known as the Cassiopeia window. The window opens up in central Cepheus, stretches right across the constellation of Cassiopeia, and ends at the Perseus double cluster. When looking through the Cassiopeia window, you can see the next outward arm of our galaxy, the Perseus arm.

NGC 457 is one of the clusters that are situated in the Perseus arm. It lies at a distance somewhere between 2.5 and 3-kilo parsecs (8,000 to 10,000 light years).
On the image below you see our Sun as an orange dot in the "Orion spur", a part of our own spiral arm. NGC 457 is the yellow dot in the Perseus arm. Here you can see that we have to look through our own arm and the inter-arm gap to see NGC 457 in the Perseus arm. With galactic latitude of -4.4, NGC 457 is situated well within the plane of the spiral arm.
The next image should give you an idea about the distribution of the open clusters you see in the direction of Cassiopeia. The clusters are plotted as yellow dots (not all clusters are plotted, you can observe 100+ open clusters in the constellation of Cassiopeia!). As you can see, two are situated within our own spiral arm (NGC 225 and NGC 189), some of the open clusters lie in the inter-arm gap (M 52, NGC 129, and NGC 7789), but most of them are members of the Perseus arm, just like NGC 457. The lonely cluster at the far side of the Perseus arm is NGC 136.
By the way, the 5 stars that form the "W" of Cassiopeia are all foreground stars, that lie within our own spiral arm.

Phi Cassiopeia, the brightest star in NGC 457 (or not?)

In most publications, Phi Cassiopeia is considered to be the brightest member of NGC 457. It is also stated that Phi Cassiopeia is a yellow supergiant or even hypergiant. But according to Jim Kaler, things are not always that simple with stars and their distances. It has everything to do with measuring the distance, which is one of the most difficult things in astronomy. Phi Cassiopeia probably lies at a distance of 4500 light years, which would make it a foreground star, and not a member of NGC 457. That's why I put a questionmark where there should be a magnitude for the "brightest star" in the cluster data at the beginning of this page.To read more about Phi Cas, please follow this link to Jim Kaler's excellent website on stars.