Shallow Sky Object of the Month: Collinder 69 (Cr69) Orion’s Head

Original article appears in GuideStar March, 2016.

by Bill Pellerin, GuideStar Editor

Object:  CR69—Orion’s Head
Class:  Open Cluster
Constallation:  Orion
Magnitude:  Stars 3.4 and dimmer
R.A.:    5 h, 35 m, 8.3 s
Dec:    9°  52’ 3”
Size/Spectral:  1 degree field
Distance:  1055 ly to Meissa (brightest star)
Optics needed: Binocs or small telescope

This set of stars comprising Orion’s head is easy to spot. Find the top two stars of the constellation, comprising the shoulders of Orion, named Betelgeuse and Bellatrix. Cast your eye about halfway between them then move up (north) about 3 degrees to find this cluster.

You should see about 10 stars with your binoculars and perhaps 50 stars in a small telescope. It’s a fairly dense star field so picking out stars that are part of the cluster from those that just happen to be along the line-of-sight to the cluster may be difficult.

The object is well placed in the sky with a transit time (mid March) of 7:15 p.m. and a set time of 1:40 a.m. You have plenty of time to get a look at this one in your telescope, but it’ll be best, meaning highest in the sky, earlier in the evening.

If you have a go-to telescope you can enter the star name Meissa (Lambda (λ) Ori) to find the cluster. Meissa is the brightest star in the cluster at 3.4 magnitude. Meissa is a double star whose 5.5 magnitude companion is 4.4 arc-seconds to the northwest of its companion.  Meisa is a very hot (35,000° K) star that provides 65,000 times the energy of our Sun. It is so powerful that it ionizes (lights up) a very large cloud of dust and gas in the constellation.

Since the stars that comprise the cluster are related to each other by birth, they’re all approximately the same distance (1300 ly) from us.

As is often the case the catalog that includes this cluster’s designation CR69 is less well celebrated that some of the other catalogs that are familiar to amateur astronomers (Messier, NGC, Caldwell, etc.). The Collinder catalog lists 471 open clusters, originally identified by Per Collinder, a Swedish astronomer. Cr 399 is well known to most of us as ‘The Coathanger’ in the summer sky.

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