First Light Guide #3: NGC225

NGC 225, the "Sailboat Cluster"

A detailed guide to finding / observing the open cluster

First Light Guide 3 graphicFirst Light Guides #3 is a detailed written and video reference to finding and observing the open cluster NGC 225 in the constellation of Cassiopeia. This guide is ideal for beginners, but many advanced amateur astronomers may find it useful. Note that NGC 225 is sometimes known as the "Sailboat Cluster" due to its outline (see Observing Notes below). This guide will help you locate this open cluster with almost any telescope set up. 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 225 in the sky

NGC 225 is an open cluster within our own Milky Way galaxy. It is over 2,100 light years from Earth, so the photons from it reaching your eye in a telescope left that cluster over 100 years before the Common Era began. The cluster was first discovered by Caroline Herschel on September 23, 1783. The cluster was thought to be 120 million years old, but recent spectral evidence suggests that it is likely much younger, a mere ~10 million years of age (quite young as open clusters are concerned).

If you have a magnified finderscope on your telescope, start here to find NGC 225:

If you have a red dot finder on your telescope, start here to find and observe NGC 225:

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 225:

Observing tips:

NGC 225 really does look a lot like a sailboat shape. It also tends to stand out fairly well from the Milky Way background in this area of sky. There are about 2 dozen or so stars that form the "boat" and "sail" shape for this cluster that are 12.0 magnitude or brighter. The brightest star glows at magnitude 9.3, while the faintest ones just help add to the shape of most of the other 9-th and 10-th magnitude suns. 

Being an open cluster, most of the stars in the cluster will shine through light pollution fairly well. Keep in mind that more will be seen with a smaller telescope in darker skies, and if viewing through city light pollution, telescope of 114mm to 150mm or larger may be required. Because this cluster is approximately 12 arc minutes across - or nearly quarter of a degree - a medium field of view is best to frame it well. Start with a wide field of view to locate the cluster, then use an eyepiece that provides your telescope with a 1/2 degree to 3/4 degree field of view for best viewing. 

Useful filter(s): None; a filter will likely just dim the stars and make the cluster harder to see.

What should I see?

Below is an approximate view of NGC 225 as seen with a 70mm telescope at 60x magnification, and a 0.90 degree telescopic field of view. The "sail" is at the the center/bottom/left. This 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 generate 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 NGC225 through a small telescope

Details of NGC 225

Type: Open star cluster

Distance: 2,143 light years 

Apparent dimensions: ~12 arc minutes

Apparent magnitude: 7.0

Right ascension: 0h 43m 24.0s

Declination: +61 47' 00"

Because telescopes and observers are all different, here are some alternate sketched/drawn views of NGC 225:

NGC225 at 70x

George Sauter, 8" SCT

Looking for other nearby First Light Guide objects? Here's some to consider:

Double star: Eta Cassiopeiae

Open cluster: NGC 457

Double open cluster: NGC 869 / NGC 884

Spiral / dwarf galaxies: Messier 31 / 32

Variable star: Delta Cephei

The constellation: Cassiopeia

General information about Cassiopeia, the Queen, where NGC225 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).