When is the best time to observe Caldwell 13?

Caldwell 13 is best observed from September through November, with peak visibility during October when it transits around midnight in the Northern Hemisphere.

Where is Caldwell 13 located in the sky?

Caldwell 13 lies in the constellation Cassiopeia at right ascension 01h 19m and declination +58° 20′.

What telescope do I need to see Caldwell 13?

At magnitude 6.4, Caldwell 13 is easy in 7×50 or 10×50 binoculars.

Caldwell 13 — Open Cluster in Cassiopeia

NGC 457

Open Cluster Excellent (70/100)

Magnitude 6.4^m OpenCluster Cassiopeia Visible

Credit: Chuck Ayoub. License: CC0. (Wikimedia Commons)

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About Owl Cluster

Description

The Owl Cluster (NGC 457) is a bright open cluster in Cassiopeia, about 7,900 light-years away. It features two bright stars that form the "eyes" of an owl with wings spread, giving it its popular name. The cluster spans about 13 arcminutes.

Observing Tips

One of the most delightful open clusters for beginners. Even a small telescope reveals the owl pattern clearly. The bright star Phi Cassiopeiae marks one eye. Best at 40-60x to frame the entire figure. Circumpolar and best in autumn.

History

Discovered by William Herschel in 1787. Also known as the E.T. Cluster because some observers see the outline of the movie character E.T. instead of an owl.

Fun Facts

Whether Phi Cassiopeiae (the bright yellow star forming one eye) is actually a cluster member or a foreground star is debated. If it is a member, it would be one of the most luminous supergiants known.

Observe

1Properties

Magnitude 6.4

Angular Size 7.8′

Distance 7,900 ly

Description

Open Cluster [Distance: 7900 ly]

Position & Identifiers

RA 01h 19m 30.0s

Dec +58° 19' 58.8"

Constellation Cassiopeia

Catalog C13

Also known as NGC 457

Physical size

20 light-years across — about 2.4× the Sun-to-Sirius distance

2How easy to spot?

Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Easy	Easy	Easy
150 mm Newton 150mm Newt.	Easy	Easy	Easy
Celestron C8 (203 mm SCT) C8 203mm	Easy	Easy	Easy

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

Easy on Seestar S50

At 150mm under B5 skies you should resolve about 88 of 508 members.

3Visibility

Set a location in User Settings to see visibility data.

Best season Sep – Nov (peak: Oct)

4 Eyepiece View

Telescope Eyepiece

125x TFOV: 0.4° Lim. mag: 13.6

Owl Cluster · 7.8′ diameter

5 Best Magnification

6Where this cluster sits in time

Open clusters span more than four orders of magnitude in age — from newborn OB associations to ancient, metal-rich survivors.

7 Colour-Magnitude Diagram

A cluster's colour-magnitude diagram reveals its age: the bluer the turn-off point where the main sequence bends into red giants, the younger the cluster.

Loading member data…

Each point is a Gaia-DR3 member. Colour encodes spectral type; size reflects membership probability.