When is the best time to observe Caldwell 75?

Caldwell 75 is best observed from April through June, with peak visibility during May when it transits around midnight in the Northern Hemisphere.

Where is Caldwell 75 located in the sky?

Caldwell 75 lies in the constellation Scorpius at right ascension 16h 25m and declination -40° 39′.

What telescope do I need to see Caldwell 75?

At magnitude 5.8, Caldwell 75 is easy in 7×50 or 10×50 binoculars.

Caldwell 75 — Open Cluster in Scorpius

NGC 6124

Open Cluster Showpiece (86/100)

Magnitude 5.8^m OpenCluster Scorpius Visible

Credit: Legacy Surveys / D.Lang (Perimeter Institute) & Meli thev. License: CC BY 4.0. (Wikimedia Commons)

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About C75

Description

NGC 6124 is a large, bright open cluster in Scorpius, about 1,600 light-years away. It contains about 100 stars spread across 29 arcminutes, with the brightest members at magnitude 8-9.

Observing Tips

A fine cluster for binoculars and small telescopes. The large angular size is best appreciated at low power. Several color contrasts among the brighter stars. Located in the rich Scorpius Milky Way. Best in summer evenings.

History

Discovered by Nicolas Louis de Lacaille in 1751 from South Africa. One of many southern clusters discovered during his pioneering sky survey.

Fun Facts

NGC 6124 is about 140 million years old, old enough that some of its stars have evolved into orange and red giants, providing nice color contrast against the blue-white main-sequence members.

Observe

1Properties

Magnitude 5.8

Angular Size 13.5′

Distance 1,500 ly

Description

Open Cluster [Distance: 1500 ly]

Position & Identifiers

RA 16h 25m 20.2s

Dec -40° 39' 14.4"

Constellation Scorpius

Catalog C75

Also known as NGC 6124

Physical size

8.4 light-years across — about 1.9× the Sun-to-Alpha-Centauri 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 230 of 800 members.

3Visibility

Set a location in User Settings to see visibility data.

Best season Apr – Jun (peak: May)

4 Eyepiece View

Telescope Eyepiece

125x TFOV: 0.4° Lim. mag: 13.6

C75 · 13.5′ 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.