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Sigma Geminorum — Star in Gemini

Magnitude 4.1–4.3m Star Gemini (Gem) Visible
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1Physical Properties

Magnitude 4.28
Range 4.13 - 4.29
Period 19.4 days
Variable Type RS CVn (Chromospherically Active)
Spectral Type K1III giant
Star Color Orange (B-V 1.12)
Distance 181 ly

2Position & Identifiers

RA 07h 43m 18.7s
Dec +28° 53' 01.0"
Constellation Gemini (Gem)
HR 2973
HIP 37629
HD 62044
SAO 79638
Bayer Sigma
Flamsteed 75 Gem
Variable ID Sig Gem
SIMBAD

3How easy to spot?

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Equipment Bortle 3 Bortle 4 Bortle 5
Naked eye Medium+ Medium+ Medium
50mm finder Easy Easy Easy
150mm scope Easy Easy Easy
Easy Medium Hard Very hard Impossible

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

4Visibility

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Best season Dec – Feb (peak: Jan)

5Survey Image

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7

Size Comparison

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8

Compare Stars

9

Spectral Classification

10

Hertzsprung-Russell Diagram

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Read: The Hertzsprung-Russell Diagram — Reading Stars Like a Map
11

Stellar Lifecycle

12

Blackbody Spectrum

13

Stellar Absorption Spectrum

Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.

14

Stellar Fusion

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15Stellar Notes

RS 4.13 - 4.29V, 19.423d.
19.605d, K 34.2k/s, V0 +45.8k/s, asini 9.22. Possible radio binary.
Eta Cep group.
H alpha emission.
16

Light Travel Time Machine

17

Relativistic Travel

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.

Pollux
HIP 37826; Beta Geminorum; 78 Geminorum
Easy
Bright naked-eye star, mag 1.1
Star mag 1.14 1.0° Gemini
Upsilon Gem
Easy
Cool red giant
Star mag 4.06 2.6° Gemini
Castor
HIP 36850; Alpha Geminorum; 66 Geminorum
Easy
Easy double, sep 5.7″
Double Star mag 1.98 3.5° Gemini
NGC 2420
Easy
Open cluster
Open Cluster mag 8.3 7.4° Gemini
Eskimo Nebula
NGC 2392
Medium+
Small bright planetary nebula
Planetary Nebula mag 9.2 8.6° Gemini
Show on Map

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