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Theta Ophiuchi, 42 Ophiuchi, HD157056, HIP84970, HR6453

Theta Ophiuchi is a blue pulsating subgiant star that can be located in the constellation of Ophiuchus. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Theta Ophiuchi's Alternative Names

Theta Ophiuchi is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR6453. HIP84970 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD157056.

Theta Ophiuchi has alternative name(s) :- , the Oph.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 42 Ophiuchi with it shortened to 42 Oph.

The Gould star designation is one that was designed by American astronomer, Benjamin Apthorp Gould. Gould stars are predominantly in the Southern and Equatorial constellations but do appear in northern constellations such as Bootes and Orion. The star has the designation 126 G. Ophiuchi. There are no stars with a Gould designation in Ursa Major for example.

More details on star alternative names can be found at Star Names.

Location of Theta 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 Theta Ophiuchi, the location is 17h 22m 00.58 and -24° 59` 58.2 .

Proper Motion of Theta Ophiuchi

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -23.94 ± 0.09 miliarcseconds/year towards the north and -7.37 ± 0.17 miliarcseconds/year east if we saw them in the horizon. The Radial Velocity, that is the speed at which the star is moving away/towards us is -2.10000 km/s with an error of about 3.60 km/s .

Theta Ophiuchi Luminosity

Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 2762.2200000 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of Theta Ophiuchi

Theta Ophiuchi has a spectral type of B2IV. This means the star is a blue subgiant star. The star is 7267.00000000 Parsecs from the Galactic Centre or terms of Light Years is 23702.2902084800000000s. The star has a B-V Colour Index of -0.18 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 15,433 Kelvin.

Theta Ophiuchi Radius has been calculated as being 5.01 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 3,487,512.60.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 3.87. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Theta Ophiuchi Apparent and Absolute Magnitudes

Theta Ophiuchi has an apparent magnitude of 3.27 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 -2.92 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.36. 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 Theta Ophiuchi

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 5.79 which gave the calculated distance to Theta Ophiuchi as 563.32 light years away from Earth or 172.71 parsecs. It would take a spaceship travelling at the speed of light, 563.32 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

In 2007, Hipparcos data was revised with a new parallax of 7.48 which put Theta Ophiuchi at a distance of 436.05 light years or 133.69 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.

The star's Galacto-Centric Distance is 7,267.00 Parsecs or 23,702.29 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Theta Ophiuchi

The star is a pulsating Beta Cephei 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. Theta Ophiuchi brightness ranges from a magnitude of 3.205 to a magnitude of 3.184 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.1 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.

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Theta Ophiuchi Facts

Visual Facts

Alternative NamesHD 157056, HIP 84970, HR 6453, 126 G. Ophiuchi, 42 Ophiuchi, 42 Oph, the Oph
Star TypeSubgiant Star
GalaxyMilky Way
Absolute Magnitude-2.92 / -2.36
Visual / Apparent Magnitude3.27
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)17h 22m 00.58
Declination (Dec.)-24° 59` 58.2
Galactic Latitude6.55 degrees
Galactic Longitude0.46 degrees
1997 Distance from Earth5.79 Parallax (milliarcseconds)
 563.32 Light Years
 172.71 Parsecs
2007 Revised Distance from Earth7.48 Parallax (milliarcseconds)
 436.05 Light Years
 133.69 Parsecs
Galacto-Centric Distance23,702.29 Light Years / 7,267.00 Parsecs
Proper Motion Dec.-23.94 ± 0.09 milliarcseconds/year
Proper Motion RA.-7.37 ± 0.17 milliarcseconds/year
B-V Index-0.18
Radial Velocity-2.10 ± 3.60 km/s
Semi-Major Axis7113.00
Stellar Luminosity (Lsun)2,762.22
Spectral TypeB2IV
Colour(B) blue

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeBeta Cephei
Mean Variability Period in Days0.141
Variable Magnitude Range (Brighter - Dimmer)3.184 - 3.205

Estimated Facts

Calculated Effective Temperature15,433 Kelvin

Sources and Links

SIMBAD SourceLink

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

Location of Theta Ophiuchi in Ophiuchus

Theta Ophiuchi (Theta Ophiuchi) Location in Ophiuchus

The map was generated using Night Vision, an awesome free application by Brian Simpson.

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