First Light Guide #7: NGC663

NGC 663

A detailed guide to finding / observing the open cluster

First Light Guide 7 graphicFirst Light Guides #7 is a detailed written and video reference to finding and observing the open cluster NGC 663 in the constellation of Cassiopeia. This guide is ideal for beginners, but many advanced amateur astronomers may find it useful. Note that NGC 663 is sometimes also known as Caldwell 10. 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 663.

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 637 in the sky

NGC 663 is an open cluster within our own Milky Way galaxy. It is over 6,800 light years from Earth, so the photons from it reaching your eye in a telescope left that cluster about the time circular ditches - such as the Goseck Circle - were being dug as solar observatories in the 5th millenium BCE. NGC 663 is stil considered a young open cluster, with an estimated age around 20 million years.

If you have a magnified finderscope on your telescope, start here to find NGC 663:

If you have a red dot finder on your telescope, start here to find and observe NGC 663:

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 663:

Video not available yet, but coming soon!

Observing tips:

This is a good cluster for helping the observer understand what kind of viewing conditions they have, and what magnitude of stars their telescope will reveal. NGC 663 is not as small as NGC 637, but it is only 16 arc minutes across in total, or just over 1/4 of a degree. So higher magnification will help in a couple of ways; one, it will frame the cluster nicely at a 1/2 to 2/3 degree field of view, and two, the higher power will darken the sky background, often assisting in revealing more stars.

How many more stars? There are about 10 of them that are 9-th to 10-th magnitude. That alone makes the cluster worth finding. These will be the easiest to find and see from most anywhere. But at 11-th magnitude (down to 11.4), close to 20 more can be seen. Add a bit more aperture, and for 12-th magnitude, and as many if not more are now observable. A 6" telescope at 100x to 150x magnification under reasonably dark suburban skies can show a lovely cluster and stars down to 13.5 magnitude, make this a magnificent sight. 

So aperture and magnification will help. Use both as you can, just don't overdo the magnification. 

Useful filter(s): None necessary

What should I see?

Below is an approximate view of NGC 663 as seen with a 70mm telescope at 60x magnification, and a 0.9 degree telescopic field of view.  

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 NGC663 as seen through a small telescope

Details of NGC 663

Type: Open star cluster

Distance: 6,850 light years 

Apparent dimensions: 16 arc minutes

Apparent magnitude: 7.1

Right ascension: 01h 46m 0.0s

Declination: +61 15' 00"













Because telescopes and observers are all different, here are some alternate sketched / drawn views of NGC 663:

Jeremy Perez, 6" f/8 at 120x

Mike M, 16" at 84x


The constellation: Cassiopeia

General information about Cassiopeia, the Queen, where NGC663 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 catalog (link here).