Tonight

See the Double Cluster in Perseus

Posted by

and

February 3, 2021

Star chart of constellations Cassiopeia and Perseus with two small circles of dots between them. — Cassiopeia and Perseus, guides to the Double Cluster.

Finding the Double Cluster

Tonight, find the gorgeous Double Cluster in the constellation Perseus. It’s a wonderful sight to see, assuming your sky is dark. To see it at this time of year, face north to northwest as darkness falls. The Double Cluster consists of two open star clusters, known as H and Chi Persei (also called NGC 884 and 869).

How to find them? First, you really do need that dark sky. Second, you might need binoculars, as the Double Cluster is only faintly visible to the unaided eye, even on an inky black night. Look for the famous constellation Cassiopeia the Queen in the northwest, forming a backwards “3,” or perhaps an “E,” or the letter “M” or “W” turned on its side.

Just above Cassiopeia, assuming your sky is dark enough, you’ll see a faint fuzzy patch. This is the Double Cluster, which blooms into a sparkling array of stars through binoculars or a small backyard telescope.

EarthSky lunar calendars are still available! We’re guaranteed to sell out – get one while you can.

Star field with constellation Cassiopeia and line pointing to the double cluster. — Finding the Double Cluster with the constellation Cassiopeia. Image via madmiked/ Flickr.

Science of the Clusters

These two open star clusters reside an estimated 7,400 light-years away. Each contains 300 to 400 stars. These stars are thought to be approximately three million years old … babies in star time! The stellar gas and the myriad stars that compose the flat disk of our Milky Way galaxy pass right through Cassiopeia and Perseus – and in front and behind the Double Cluster. If your sky is dark enough, you’ll see the hazy pathway of the winter Milky Way crossing this part of the sky.

Double Cluster in antiquity

The Double Cluster was charted by skywatchers as early as 150 B.C. Hipparchus saw it, and Ptolemy named it as one of seven “nebulosities” in the Almagest, an ancient astronomy text used for over a millennium. The Double Cluster in Perseus ranks as a favorite among stargazers, a bejeweled place in the heavens to zoom in on with binoculars.

Deborah Byrd

View Articles

About the Author:

Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.