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NGC 2158 — Open Cluster in Gemini

Open Cluster Good (48/100)
Magnitude 8.6m OpenCluster Gemini (Gem) Visible
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1Properties

Magnitude 8.6
Angular Size 8.4′
Cl, pS, mC, vRi, irr triangle st eS

Position & Identifiers

RA 06h 07m 25.6s
Dec +24° 05' 46.3"
Constellation Gemini (Gem)
Catalog NGC 2158
Physical size
34 light-years across — about 4.0× 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 18 of 800 members.

3Visibility

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Best season Nov – Jan (peak: Dec)

4 Eyepiece View

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125x TFOV: 0.4° Lim. mag: 13.6
N E

NGC 2158 · 8.4′ diameter

5 Best Magnification

6Where this cluster sits in time

1 Myr 10 Myr 100 Myr 1 Gyr 10 Gyr NGC 2362 Pleiades Hyades M67 NGC 188 NGC 2158 1.5 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.

M35
NGC 2168
Easy
Open cluster
Open Cluster mag 5.1 0.4° Gemini
IC 2157
Easy
Open cluster
Open Cluster mag 8.4 0.6° Gemini
3 Gem
Easy
Variable star, range 7.0–10.0
Variable Star mag 5.75 1.1° Gemini
NGC 2129
Easy
Rich open cluster
Open Cluster mag 6.7 1.6° Gemini
Collinder 89
Easy
Open cluster
Open Cluster mag 5.7 2.5° Gemini
M1
Crab Nebula
Medium+
Supernova remnant
Supernova Remnant mag 8.4 7.8° Taurus
Show on Map

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