1 Serpentis
{{Short description|Red giant star in the constellation Virgo}}
{{Starbox begin}}
{{Starbox image
| image=
{{Location mark
|image=Serpens Caput IAU.svg|alt=|float=center|width=280
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=1 Ser
|x=758|y=838
}}
|caption=Location of 1 Serpentis (circled)
}}
{{Starbox observe
| constell = Virgo
| equinox = J2000.0
| epoch = J2000.0
}}
{{Starbox character
| type = Red clump
| variable =
}}
{{Starbox astrometry
| prop_mo_dec = {{val|-26.500}}
| parallax = 10.1280
| p_error = 0.1010
}}
{{Starbox detail
}}
{{Starbox catalogue
| names={{odlist|F=1 Ser|BD=+00°3277|GJ=3881|HD=132132|HIP=73193|HR=5573|SAO=120758}}
}}
{{Starbox reference
| Simbad = 1+Ser
}}
{{Starbox end}}
1 Serpentis (1 Ser) is a red giant in the constellation Virgo with an apparent magnitude of 5.5. It is a red clump giant, a cool horizontal branch star that is fusing helium in its core. It has expanded to over 13 times the radius of the Sun and although it is cooler at {{val|4,581|fmt=commas|ul=K}} it is 77 times more luminous. It is 322 light years away.
The Flamsteed designation 1 Serpentis was given to the star when the constellation Serpens was combined with the constellation Ophiuchus. It was also given the Bayer designation M Serpentis. When Ophiuchus and Serpens were separated into distinct constellations, 1 Serpentis was left over the border in Libra. Since then it has moved slightly and is now in Virgo.
A 10th-magnitude companion star discovered by William Herschel is {{val|86|ul="}} away. It is at the same distance as 1 Ser and shares a common proper motion, It is considered likely to be a physical companion, with the two stars separated by {{val|8,600|fmt=commas|ul=au}}. It has a spectral type of G5 IV, and it is slightly smaller and less luminous than the sun.
A much more widely-separated 10th-magnitude star is also listed in multiple star catalogues, but it is an unrelated background object.
References
{{reflist|refs=
{{cite Gaia DR3|3650900223700313088}}
{{cite DR2|3650900086261359232}}
{{cite DR2|3650886479804959360}}
}}
{{Stars of Virgo}}
{{Authority control}}
{{DEFAULTSORT:1 Serpentis}}
Category:Virgo (constellation)