First Light Guide #5: NGC457

NGC 457, the "E.T. Cluster"

A detailed guide to finding / observing the open cluster

First Light Guide 5 graphicFirst Light Guides #5 is a detailed written and video reference to finding and observing the open cluster NGC 457 in the constellation of Cassiopeia. This guide is ideal for beginners, but many advanced amateur astronomers may find it useful. Note that NGC 457 is sometimes known as the "E.T. Cluster" due to its resemblance to the 1980's movie character. It is alternately known as the "Dragonfly Cluster" or "Owl Cluster" as the shape can resemble a dragonfly or owl with outstretched wings. This guide will help you locate this open cluster with almost any telescope. There is a video to using a magnified finderscope, red dot finder, or setting circles along written tips on observing NGC 225.

Visitors who are new to this site may wish to get started here, while more advanced observers can search the First Light Guides by constellation, or by right ascension

Find NGC 457 in the sky

NGC 457 is an open cluster within our own Milky Way galaxy. It is over 7,900 light years from Earth, so the photons from it reaching your eye in a telescope left that cluster about the time copper was being used in the Middle East. The estimated age is about 21 million years, making it one of the younger star clusters in our galaxy.

If you have a magnified finderscope on your telescope, start here to find NGC 457:

If you have a red dot finder on your telescope, start here to find and observe NGC 457:

If you have a telescope that has an equatorial mount with fairly precise setting circles, you may find this video useful when trying to find NGC 457:

Video not available yet, but coming soon!

Observing tips:

NGC 457 is called the "E.T." or "Owl" cluster for good reason: There appear to be two prominent "eyes" and then a fainter body with arms - or wings - outstretched. So imagine E.T. like this (except with it's arms outstretched on either side) or an owl like this, and you have some idea of what to expect at the eyepiece. 

The most notable thing to look for is the "eyes" though. One will appear slightly blue; this is a B-class star over 5,000 light years away. The other to me appears somewhat yellow-ish in comparison, even though it is a more pure-white F-class star more than 2 times as far away at 12,000 light years. Neither of these belong to the cluster, however, that sits between these two stars' distance at around 8,000 light years. This cluster truly is a chance line-of-sight phenomenon. In a magnified finder, the "eyes" are easy to see when searching for the object; given it's overall size at 13 arc minutes, beginning with a lower magnification that yields 1 degree or more is a good idea. 

Useful filter(s): None required. 

What should I see?

Below is an approximate view of NGC 457 as seen with at 60x magnification with a 0.90 degree field of view. Not that depending on the orientation of Cassiopeia in the sky, and your telescope's mirrors, the view may be significantly rotated or even upside down compared to what is shown here. Most of the stars are high 10th to low 12-th magnitude, meaning most are similarly bright at the eyepiece, and also visible in most any telescope under most sky conditions.  

Graphic demonstrates how view would look with objects on the meridian using a refractor telescope and a star diagonal.  Other telescopes or object sky positions may incur a differing view.  Various magnifications, eyepieces, telescope focal lengths and other variables may alter the view compared to this one.  This is a representation only intended to help the observer get some idea what they may see at the eyepiece.  Extreme local light pollution may block the view entirely.

Approximate view of NGC457 as seen through a small telescope

Details of NGC 457

Type: Open star cluster

Distance: 7,922 light years 

Apparent dimensions: 13.0 arc minutes

Apparent magnitude: 6.4 (integrated)

Right ascension: 01h 19 6.0s

Declination: +58 20' 00"

Because telescopes and observers are all different, here are some alternate sketched/drawn views of NGC 457:

Jeremy Perez, 15x70 binoculars 

Sebastian, 114mm reflector

The constellation: Cassiopeia

General information about Cassiopeia, the Queen, where NGC457 is located. This will help you know where to find the constellation in the sky and be able to locate and identify its brightest stars.

Name of constellation: Cassiopeia

Abbreviation: Cas

Genetive form: Cassiopeiae

Common names: The Queen, Ethiopian Queen

Associated asterisms: Five brightest stars form a "W" or "M" shape depending on the time of night/year

Original 48 of Ptolemy: Yes

Area by size: 598 square degrees

Relative size: 25 out of 88 (Perseus is next larger, Orion is next smaller)

First Light Guides objects: Eta Cassiopeiae, NGC225, NGC457, NGC663, NGC637

Brightest stars, in order of magnitude 

First lists the Bayer designation, then the "traditional" star name (often Arabic, but not always - see each star's notes for details).

  • α (Alpha) Cassiopeiae (Schedar, Shedir) magnitude 2.25, the 71st brightest star in the sky. The traditional name is derived from the Arabic word صدر şadr, meaning "breast," appropriate for a queen constellation.

  • β (Beta) Cassiopeiae (Caph) magnitude 2.27, is the 73rd brightest star in the sky. Its name comes from a pre-Islamic Arabic term al-Kaff al-Khadib which means "the stained hand" (referring to stain from henna). .

  • γ (Gamma) Cassiopeiae (Tsih, Navi) magnitude 2.39, is 82nd brightest star in the sky. However, it is also somewhat variable, dropping as low as 3.0, and as bright as 1.6. The star has no traditional Arabic name. "Tsih" comes from Chinese, derived from the word "whip." A nickname was applied to the star by American astronaut Gus Grissom; his middle name was "Ivan" and spelled backwards, it is "Navi."

  • δ (Delta) Cassiopeiae (Ksora, Ruchbah) magnitude 2.68. It is an Algol-type eclipsing variable star, with a period of 2 years/1 month, and varies by 0.1 magnitude. The traditional names are from the Arabic word ركبة rukbah meaning "knee."

  • ε (Epsilon) Cassiopeiae, magnitude 3.35. It has no traditional Arabic name assigned to it. 

  • η (Eta) Cassiopeiae, magnitude 3.45. It has no traditional Arabic name assigned to it. It is a very Sun-like star in size, mass and luminosity. This is a double star highlighted in the First Light Guides (link here).