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IC 4756 — Open Cluster in Serpens

Open Cluster Excellent (62/100)
Magnitude 5.0m OpenCluster Serpens (Ser) Visible
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1Properties

Magnitude 5.0
Angular Size 24.0′
Cl, C

Position & Identifiers

RA 18h 38m 51.5s
Dec +05° 27' 43.9"
Constellation Serpens (Ser)
Catalog IC 4756
Physical size
12 light-years across — about 1.3× the Sun-to-Sirius distance

2How easy to spot?

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Telescope Bortle 3 Bortle 4 Bortle 5
80mm refr. Easy Easy Easy
150mm Newt. Easy Easy Easy
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 208 of 463 members.

3Visibility

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Best season May – Jul (peak: Jun)

4 Eyepiece View

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50x TFOV: 1.0° Lim. mag: 13.6
N E

IC 4756 · 24.0′ diameter

5 Best Magnification

6Where this cluster sits in time

1 Myr 10 Myr 100 Myr 1 Gyr 10 Gyr NGC 2362 Pleiades M67 NGC 188 IC 4756 1.3 Gyr

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.

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8 Classification Decoder

Nearby in the Sky

Other targets within a few degrees — pan your scope a little and keep exploring.

Visibility scores assume a 150 mm Newton at Bortle 4.

Tweedledee Cluster
NGC 6633
Easy
Rich open cluster
Open Cluster mag 4.6 3.1° Ophiuchus
X Oph
Easy
Mira-type variable, range 5.9–9.2
Variable Star mag 6.40 3.4° Ophiuchus
Alya
HIP 92946; Theta1 Serpentis; 63 Serpentis
Easy
Easy double, sep 22.4″
Double Star mag 4.62 4.5° Serpens
NGC 6709
Easy
Rich open cluster
Open Cluster mag 6.7 5.8° Aquila
NGC 6572
Medium+
Small bright planetary nebula
Planetary Nebula mag 9.0 6.8° Ophiuchus
NGC 6755
Easy
Open cluster
Open Cluster mag 7.5 7.3° Aquila
NGC 6756
Medium+
Open cluster
Open Cluster mag 11.0 7.5° Aquila
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