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Sigma Sagittarii, 34 Sagittarii

Proper NameNunki
Bayer DesignationSigma Sagittarii
Flamsteed Number34 Sagittarii
HR (BSC)7121
Right Ascension18h 55m 16s
Declination-26° 17' 48"
Distance228 light years
70 parsecs
MagnitudeApparent: +2.1
Absolute: -2.2
Spectral ClassB2V Blue Dwarf
Optimum VisibilityJuly
NotesThe brightest of the five stars that make up the 'Milk Dipper' formation at the heart of Sagittarius, marking the flights of the arrow raised by the Archer. The name Nunki is extremely ancient, being derived from Babylonian texts, and though meaning is unclear, it seems to have been associated with the ocean.

Nunki is a hot blue star in the central regions of Sagittarius, in the belt of the Milky Way. Like all Sagittarius' stars, it lies in the direction of the Galaxy's core, and is also close by the line of the Ecliptic.

Imagery provided by Aladin sky atlas

The mass of this star is comparable to that of the Sun (in other words, it lies among the Main Sequence, or Dwarf, stars), although its surface temperature of about 8,000 K is roughly twice that of our own star. Nunki also differs from the Sun in being a binary: in common with many stars, it has a fainter companion.

From Earth, Nunki has a magnitude of +2.1 (equivalent to Alpheratz or Mirach, both in Andromeda), but this is largely due to its great distance, more than 200 light years from the Sun. At ten parsecs (the standard for measuring absolute magnitude) it would shine with a magnitude of -2.14, brighter even than Sirius.


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