· · · ·

Yed Posterior

Epsilon Ophiuchi, 2 Ophiuchi

Proper NameYed Posterior
Bayer DesignationEpsilon Ophiuchi
Flamsteed Number2 Ophiuchi
HR (BSC)6075
Right Ascension16h 18m 19s
Declination-4° 41' 33"
Distance106 light years
33 parsecs
MagnitudeApparent: +3.2
Absolute: +0.7
Spectral ClassG9.5IIIbFe-0.5 yellow giant
Optimum VisibilityJune
NotesThis yellow star has undergone a transition to the giant class, evolving to produce energy by fusing helium rather than hydrogen, and in the process expanding to become a giant star some ten times the Sun's diameter.
Location of Yed Posterior

With Yed Prior, Yed Posterior shares a small square patch of sky that connects the body of Ophiuchus with its neighbouring zodiacal constellation, Libra.

Image of Yed Posterior

A view of the Yed Posterior system. In the foreground is Epsilon Ophiuchi B, a small and faint 'satellite' star, invisible from Earth. The system's much more massive and luminous primary is seen here in the distant background.

The name 'Yed' comes from the Arabic word for 'hand': Yed Posterior and the nearby Yed Prior represent either the left and right hands of the Serpent Holder Ophiuchus, or two parts of one hand. This hand-star is known as the 'Posterior' because it crosses the sky about four minutes behind Yed Prior.

Though they appear close in the sky, the two Yeds are really some considerable distance apart. Yed Posterior is about 106 light years from the Earth: Yed Prior is 62 light years further still. The intervening space is occupied by a small white star, HR 6067, that is invisible to the naked eye.

Yed Posterior is a yellow, G-type star, which means that its structure and chemistry are similar to those of the Sun. There are differences, though: Yed Posterior is several hundred degrees cooler than the Sun, and very considerably larger.

This is a binary system: Yed Posterior's companion is relatively distant from the main star (at least 3,500 AU). It is also very faint, with an apparent magnitude of just +12 as compared to the main star's +3.2.


Related Entries