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Algenib — Star in Pegasus

HIP 1067; Gamma Pegasi; 88 Pegasi

Magnitude 2.8m Star Pegasus (Peg) Visible
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About Algenib

Description

Algenib is a blue subgiant of spectral type B2IV at magnitude 2.83 in Pegasus. Located about 390 light-years from Earth, it has a luminosity of roughly 5,840 times solar. Algenib marks the southeastern corner of the Great Square of Pegasus and is a Beta Cephei variable with a pulsation period of about 3.6 hours.

Observing Tips

Algenib sits at the lower-left (southeastern) corner of the Great Square of Pegasus. It is the faintest of the four corner stars after Markab. Its blue-white color contrasts with the orange Scheat (Beta Peg) at the opposite corner. Best observed September through January.

History

The name Algenib comes from the Arabic 'al-janb,' meaning 'the side' or 'the flank.' The same name has historically been applied to Alpha Persei (Mirfak), causing occasional confusion in older references.

Fun Facts

Algenib pulsates with a period of 3.6 hours — if you could speed up time, you would see it gently 'breathing' in size and brightness. These pulsations are driven by the same iron-opacity mechanism that powers all Beta Cephei variables.

Observe

1Physical Properties

Magnitude 2.83
Range 2.82 - 2.86
Period 3.6 hours
Variable Type Beta Cephei (Pulsating)
Spectral Type B2IV subgiant
Star Color Blue (B-V -0.23)
Distance 390 ly

2Position & Identifiers

RA 00h 13m 14.2s
Dec +15° 11' 01.0"
Constellation Pegasus (Peg)
HR 39
HIP 1067
HD 886
SAO 91781
Bayer Gamma
Flamsteed 88 Peg
Variable ID Gam Peg
SIMBAD Wikipedia

3How easy to spot?

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Equipment Bortle 3 Bortle 4 Bortle 5
Naked eye Easy Easy Easy
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 Aug – Oct (peak: Sep)

5Survey Image

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7

Size Comparison

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Spectral Classification

10

Hertzsprung-Russell Diagram

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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

Beta C 2.80 - 2.87V, 0.1517495d.
6.830713d, K 1.34k/s, V0 2.5k/s, asini 0.181Solar R.
Color excess E(B-V) = +0.01.
Lyman beta observed from COPERNICUS. Chlorine in spectrum.
RV also varies with period 0.151750125d.
ALGENIB.
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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.

NGC 57
Hard+
Elliptical galaxy
Galaxy mag 13.0 2.2° Pisces
47 Psc
Medium+
Semi-regular variable, range 4.7–5.4
Variable Star mag 5.06 4.5° Pisces
Chi Peg
Easy
Cool red giant
Star mag 4.80 5.0° Pegasus
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