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X Ophiuchi - HD172171 - HIP91389

X Ophiuchi is a orange to red pulsating giant star that can be located in the constellation of Ophiuchus. The star can not be seen by the naked eye, you need a telescope to see it.

HIP91389 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD172171.

X Ophiuchi has alternative name(s), X_Oph.

Location of X Ophiuchi

The location of the star in the galaxy is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For X Ophiuchi, the location is 18h 38m 21.13 and +08d50`02.6 .

Physical Properties (Colour, Temperature, Radius) of X Ophiuchi

X Ophiuchi has a spectral type of K1IIIv comp. This means the star is a orange to red giant star. The star has a B-V Colour Index of 1.2 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,489 Kelvin. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

X Ophiuchi Apparent and Absolute Magnitudes

X Ophiuchi has an apparent magnitude of 7.41 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Distance to X Ophiuchi

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as -25.80 which gave the calculated distance to X Ophiuchi as -126.42 light years away from Earth or -38.76 parsecs. It would take a spaceship travelling at the speed of light, -126.42 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

Variable Type of X Ophiuchi

The star is a pulsating Omicron Ceti variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. X Ophiuchi brightness ranges from a magnitude of 8.000 to a magnitude of 6.000 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 337.0 days (variability).

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

X Ophiuchi Facts

Alternative Names

Traditional/Proper NameX Ophiuchi
Short NameX Oph
Hipparcos Library I.D.91389
Bonner DurchmusterungBDD+08 3780
Henry Draper Designation172171

Visual Facts

Star Typegiant star
Visual / Apparent Magnitude7.41
Naked Eye VisibleRequires a 7x50 Binoculars - Ref: Wiki
Right Ascension (R.A.)18h 38m 21.13
Declination (Dec.)+08d50`02.6
Galactic Latitude6.90 degrees
Galactic Longitude39.35 degrees
1997 Distance from Earth-25.80 Parallax (milliarcseconds)
 -126.42 Light Years
 -38.76 Parsecs
B-V Index1.20
Radial Velocity-71.46 ± 0.27 km/s
Spectral TypeK1IIIv comp
Colour(K) Orange to Red

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeOmicron Ceti
Mean Variability Period in Days337.000
Variable Magnitude Range (Brighter - Dimmer)6.000 - 8.000

Estimated Facts

Calculated Effective Temperature4,489 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.


Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
172171+08 3780.0A0.00000-7.00000M4Red
B8.600001960

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