|Right Ascension|| 15 : 50 : 41.6 (h:m:s)
|Declination|| +15 : 08 : 00 (deg:m:s)
|Distance|| 600 (ly)
|Visual brightness|| 5.16 .. 14.4 (mag)
|Period|| 356.41 (days)
|Spectra type|| M7IIIe
The Mira variable R Serpentis is situated about 1.2 deg ESE of Beta Serpentis. Near its maximum, it is just visible to the naked eye at magnitudes around 5.7 (the Sky Catalogue 2000.0 lists its average maximum magnitude even at only 6.9, and the average minimum at 13.4, while the extremal values are 5.16 and 14.4 magnitudes). The minimum occurs 59 percent of a period after the maximum for this star; this property is sometimes referred to as a "phase" of 0.59. Typically for Mira stars, this star is a deeply red giant, with the spectral type varying between M6e near maximum and M8e near minimum during a period. R Serpentis shows a proper motion of 0.05" per year, and is receding from us at about 23 km/s. Burnham gives a distance estimate of 600 light years.
The variability of R Serpentis was discovered in 1826 by the German astronomer K.L. Harding, who had also discovered R Aquarii in 1810 or 1811, and the fourth asteroid, Juno, in 1804. There is record of a prediscovery observation of R Serpentis from a chart made by the French astronomer D'Agelet in March 1783, so that the date of one older maximum is known.
F.W. Argelander thought to have found a slight and steady decrease of this star's period between 1826 and 1868, but there is little or no evidence now for such a process: The period remains constant, as far as measurement is reliable, at least since about 1909.
Other identifications for R Serpentis: HR 5894, HD 141850, SAO 101771.
Recent and upcoming maxima: November 2008, October 2009; August 31, 2012; August 21, 2013; August 11, 2014; August 1, 2015.
Credit: Much of the information here was adopted from Burnham's Celestial Handbook, Vol. 3.