First Light Guides #18: Delta Orionis

The object: Delta Orionis

A detailed guide to finding / observing the double star in Orion

First Light Guide 18 graphicFirst Light Guides #18 is a detailed written and video reference to finding and observing the double star Delta Orionis, or Mintaka, in the constellation of Orion. This guide is ideal for beginners, but many advanced amateur astronomers may find it useful. It is designed to help you locate this double star with almost any telescope. There is a video to using a magnified finderscope, red dot finder, or setting circles along written tips on observing Mintaka.

Visitors who are new to this site may wish to get started here, while more advanced observers can search the First Light Guides by constellation, or by right ascension


Find Delta Orionis in the sky

Delta Orionis is an easily split visual double star within our own Milky Way galaxy. But it is really a multiple star system. The primary component we see visually is actually composed of a spectral class B star that is a blue giant, with a smaller and hotter O class companion, separated by 0.3 arc seconds of distance and they orbit each other in just 5.7 days. The visual component that is highlighted in this First Light guide is the easily split 52 arc seconds away 6.8 magnitude secondary.  

While the Bayer designation applied to this star is Delta Orionis, many observers are more familiar with it's Arabic name, Mintaka. It means, منطقة manṭaqa, which means "the belt" or "the giant's belt."

If you have a magnified finderscope on your telescope, start here to find Delta Orionis:


Observing tips:

Delta Orionis is an easily split double star, with a wide separation of 52 arc seconds between the brighter, 2.2 magnitude primary star(s), and the dimmer 6.8 magnitude secondary. Orion is not a zodiac constellation, but it is one of the most easily recognized shapes in the sky. It is visible from most anywhere on earth, as the celestial equator runs right through Orion's belt stars. View this star when Orion is at or near the meridian. In this way, it will be at it's highest point (culmination), providing the least amount of atmosphere to look through in order to find and observer the star. Use a long focal length eyepiece.

There is quite a bit of difference in magnitude between the primary and secondary stars, making this double a good 'starter star' for anyone looking to observe double stars of different magnitudes in the future. Look at the color difference between the brighter one and the dimmer one. How does the dimmer star's magnitude alter what you perceive for color here?  What color(s) do you see?

Useful filter(s): None needed.

What should I see?

Below is an approximate view of Delta Orionis and the surrounding stars as seen with a 70mm telescope at 38x magnification, and a 1.40 degree telescopic field of view.  

Delta Orionis as seen at 28x in a 1.4 degrees field of view

Details of Delta Orionis

Type: Double star

Orbital period: Unknown, but the dimmer secondary is ~1/4 of a light year from the primary!

Distance: 916 light years

Apparent separation: 52 arc seconds

Apparent magnitudes: 2.2, 6.8

Right ascension: 05h 32m 00.4s

Declination: -00° 17′ 57









Because telescopes and observers are all different, here are some alternate sketched/drawn views of Delta Orionis:

Jeremy Perez at 240x

The constellation: Orion

General information can be found here about Orion the Hunter, where Delta Orionis is located.  This will help you know where to find the constellation in the sky and be able to locate and identify its brightest stars.

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Name of constellation: Orion

Abbreviation: Ori

Genetive form: Orionis

Common names: The Hunter

Associated asterisms: Belt stars (three bright stars that form a "belt" across the hunter's midsection)

Original 48 of Ptolemy: Yes

Area by size: 594 square degrees

Relative size: 26 out of 88 (Cassiopeia is next larger, and Cepheus is next smaller)

First Light Guides objects: Messier 42, Delta Orionis, NGC1981, NGC2169, Struve 747, Sigma Orionis

Brightest stars, in order of magnitude 

First lists the Bayer designation, then the "traditional" star name (often Arabic, but not always - see each star's notes for details). Graphic shows the constellation on the meridian while facing south from the northern hemisphere.

  • β (beta) Orionis (Rigel) magnitude 0.18, the 7th brightest star in the sky. There is not a traditional name precisely for Rigel, but one of them that may have been attributed to it riǧl al-ǧabbār came from Arabic which meant, "Foot of the Great One."
  • α (alpha) Orionis (Betelgeuse) magnitude 0.43, the 9th brightest star in the sky. The word itself does not mean anything in any prior language, and was often spelled differently in many texts. Paul Kunitzsch, Professor of Arabic Studies at the University of Munich has proposed that the full name is a corruption of the Arabic يد الجوزاء Yad al-Jauzā' meaning "the Hand of al-Jauzā'"i.e., Orion.
  • γ (gamma) Orionis (Bellatrix) magnitude 1.62, the 27th brightest star in the sky. Traditional name comes from Latin and means "female warrior" which explains it sometimes being referred to as the "Amazon star."
  • ε (epsilon) Orionis  (Alnilam) magnitude 1.68, the 30th brightest star in the sky. It's name comes from Arabic which means "string of pearls."
  •  ζ (zeta) Orionis (Alnitak) magnitude 1.70, the 31st brightest star in the sky. It's traditional name means "the girdle."
  • κ (kappa) Orionis (Saiph) magnitude 2.05, the 52nd brightest star in the sky. The traditional name is from the Arabic saif al jabbar, ' which means "Sword of the Giant." This name was originally applied to the star now known as Eta Orionis.
  • δ (delta) Orionis (Mintaka) magnitude 2.21, is the 69th brightest star in the sky. It's traditional name is derived from Arabic, and means, "The Giant's belt."
  • ι (iota) Orionis magnitude 2.75, and is 1,325 light years distant.
  • π 3 (pi 3) Orionis magnitude 3.19, and is 26 light years distant.
  • η (eta) Orionis magnitude 3.35, and is 901 light years distant.