24 Cancri (Struve 1224): A Quaint Triple Star in Cancer

Posted byWayne McGrawPosted inDouble/Multiple StarsTags:,
Illustration of double star system

On early spring nights, the constellation of Cancer takes its prominent place on the firmament. Several stellar gems, including the wonderful Beehive Cluster and a smattering of double stars, make their home in the celestial crab. Among them is a quaint triple star in Cancer called 24 Cancri, known to astronomers since February 2, 1782, when astronomer William Hershel first spotted these stars staring back at him.

While 24 Cancri is known as a triple star system, backyard astronomers will only see two of them, 24 Cancri A and B. The third in the bunch is a binary brother to 24 Cancri B. Unfortunately, a meager 0.15 arcseconds separate the two, making the pair practically impossible to view for backyard astronomers. Nevertheless, both 24 Cancri A & B don’t disappoint in the eyepiece as a nice tight pair.

Both A & B shine white with a slight yellow tinge and are classified as F-type main sequence stars. 24 Cancri A shines at a magnitude of 6.9, while 24 Cancri B is a touch dimmer at 7.5. The pair of stars present an enjoyable challenge to separate for backyard astronomers.1

My Observations

24 Cancri is a tight double-star system with two stars of close brightness, though they are clearly not equal. Both stars appear white with a slight tinge of yellow. On this clear Ides of March night, I reflect on the alluring yet simple close pairs like this one. They are always welcome in my eyepiece, resembling two eyes looking back at me.

DateMarch 15, 2024
Time9:33 p.m.
LocationSeattle, WA
Magnification254x
ScopeMeade 8″ SCT
Eyepiece8mm
SeeingGood
TransparencyAverage
Sketch of 24 Cancri, multiple star system in the constellation Cancer. The system has a combined apparent magnitude of 6.5, and the two components A and B are separated by 5.7″ The drawing shows what the pair look like through an 8-inch SCT scope with an 8mm eyepiece under suburban skies. Also known as
Sketch of 24 Cancri on the Ideas of March 2024

Key Stats

ConstellationCancer
Best ViewingSpring
Visual Magnitude+6.9 | +7.5
Distance from Earth260 ly
Separation5.6″
Milky Way LocationOrion Spur
My Viewing GradeB
Designations24 Cnc A, HD 71152, HR 3312, SAO 80184, STF 1224, Struve 1224, upsilon

Sources and Notes

The double star banner on this page is an artist’s impression showing the double star OGLE-LMC-CEP0227 in our neighboring galaxy the Large Magellanic Cloud. This media was created by the European Southern Observatory (ESO). This file is licensed under the Creative Commons Attribution 4.0 International license.

1 Handprint. (n.d.). William Herschel’s star gages. Retrieved June 3, 2024, from https://www.handprint.com/ASTRO/Herschel_All.html

Sketch by Wayne McGraw

Leave a comment