Cancer

by Shaphan Shank | Apr 1, 2024 | 0 comments

Cancer, the Crab, is a mid-sized constellation that lies just east of Gemini and just west of Leo. Cancer is made up solely of dim stars, and its shape is not particularly distinctive, yet it has been recognized as a constellation since before the time of Christ. This constellation is fairly easy to find due to its proximity to other easily-recognizable constellations.

The main objects of interest in Cancer are its open star clusters and double stars. The most well-known of these objects is M44, the Beehive Cluster. This cluster lies in the heart of Cancer, just east of an imaginary line connecting the stars Asellus Borealis and Asellus Australis. The Beehive appears exceptionally large and bright for an open cluster; in moderately dark skies, it is easily visible to the unaided eye as a fuzzy patch of light.

The Beehive Cluster is at its finest when viewed with a binocular, or a telescope at very low magnification (<30×). This cluster is made up of a number of bright stars, and a good binocular will provide the magnification and light grasp necessary to resolve many of these stars while also showing the surrounding star field. You will be able to resolve even more stars with a telescope, but use the lowest magnification possible. At all but the lowest magnifications, the Beehive will completely fill the field-of-view, which will make it look less cluster-like.

Beehive Cluster
Beehive Cluster. Photo © Tragoolchitr Jittasaiyapan|Dreamstime.com.

Another fine open cluster, M67, lies in the southern part of Cancer, just under 2° west of the star Acubens. M67 is smaller and dimmer than M44, but it is a fine cluster nonetheless. A binocular should show this cluster as a small hazy spot of light, while a mid-sized telescope at low magnification will resolve many of its stars. M67 contains a high number of dim stars, which appear as a faint background haze in smaller telescopes.

Iota Cancri, the northernmost star in the figure of Cancer, is an outstanding example of a color-contrast double star. The primary component of this pair is gold-colored, while the slightly dimmer secondary component is pale blue. The two component stars are separated by 31 arcseconds, making the pair an easy split at low magnification. With a steady rest, you should even be able to split this double with a 10× binocular, although a telescope will give a much better view. Iota Cnc is similar in color and separation to the famous summertime double Albireo; for this reason, it is sometimes called the “Spring Albireo.”

Phi2 Cancri is another fine double in the northern part of Cancer, but it looks quite different from Iota. Phi2 Cnc consists of two white stars of equal brightness that are only separated by about 5 arcseconds. A telescope at moderate magnification will comfortably split this evenly matched pair. To find Phi2 Cnc, look for a triangle (~1° across) of faint stars about 5° west-southwest of Iota Cnc. The star in the southeastern corner of the triangle is Phi2 Cnc. This is also the faintest star in the triangle, and if your skies suffer from much light pollution, you may not be able to see the star with the unaided eye. However, it should be easy to see with binoculars.

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