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Alnitak

HIP 26727; Zeta Ori; 50 Ori

Observable Double Star Good (58/100)

Sep: 2.5", Companion: mag 3.7

HIP 26727; Zeta Ori; 50 Ori DoubleStar Ori Visible Level 4 Large telescope (10"+) - Requires steady seeing
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Physical Properties

Magnitude 2.05
Spectral Type O9.7Ib
Star Color Blue (B-V -0.21)
Distance 135.9 ly

Position & Identifiers

RA 05h 40m 45.5s
Dec -01° 56' 34.0"
Constellation Ori
HR 1948
HIP 26727
Bayer Zeta
Flamsteed 50 Ori
Double Cat 4263

Visibility

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Multiple Star System

Components 3
Component IDs AB
Separation 2.5″
Companion Mag 3.7
Companion Sp B0III
Position Angle 167°
Star Colors A: Blue B: Blue
Discoverer STF 774

Eyepiece View

80x Dawes: 1.9″ TFOV: 0.6°
Realistic = true angular size
N E 167° A (2.0) B (3.7)

Sep: 2.5″ · PA: 167° · N up, E left

Unresolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 3.1″

Size Comparison

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Stellar Lifecycle

Spectral Classification

Hertzsprung-Russell Diagram

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Blackbody Spectrum

Stellar Absorption Spectrum

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

Stellar Notes

ADS 4263. Uncertain which component, HR 1948 or 1949, is the variable suspect.
AB 1.88 O9.5Ib, 4.02 B2III, 1508.6y, a = 2.728". Colors for combined light. Blended magnitude 1.76V, 18 and 6 solar | masses. B is HR 1949. C is 9v at 58", possibly physical.
Color excess E(B-V) = +0.09.
Ori OB1b1; Orion belt; exciting star of HII region S277; HII region; IC 434.
Nitrogen deficient. Interstellar Lyman alpha absorption observed by AEROBEE rocket. Also classified O9.5Ib and | O9.5Iab.
0.004".
Mass ejection up to 1800k/s.
ALNITAK; Alnitah.
Diam. = 0.00047 - 0.00048".

Survey Image

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About Alnitak

Description

Alnitak is the easternmost star of Orion's Belt at magnitude 2.05, a hot blue supergiant of spectral type O9.7Ib. Located about 1,200 light-years from Earth, it has a luminosity of roughly 250,000 times solar — one of the most luminous stars in the Orion region. Alnitak is a triple star system; the close companion is resolvable in moderate telescopes.

Observing Tips

Alnitak is the left (eastern) star of Orion's Belt. Just south of Alnitak lies the famous Horsehead Nebula (B33) and the bright Flame Nebula (NGC 2024) — both illuminated by Alnitak's intense radiation. The Belt stars are among the easiest patterns to identify in the entire sky. Best observed December through March.

History

The name Alnitak comes from the Arabic 'al-nitaq,' meaning 'the girdle' or 'the belt.' Together with Alnilam and Mintaka, the three Belt stars have been recognized and named across virtually every culture. They were 'the Three Kings,' 'the Three Marys,' and 'the String of Pearls' in various traditions.

Fun Facts

Alnitak is responsible for illuminating the Flame Nebula and creating the silhouette of the famous Horsehead Nebula, one of the most photographed objects in the sky. The star is so energetic that its ultraviolet light ionizes the gas clouds over a light-year away.