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Struve 2398 B (Companion Star) Facts

Struve 2398 B Facts

Struve 2398 B's Alternative Names

(Struve 2398 B) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in the early nineteenth century. The brightest star in the constellation is normally given the Alpha designation although there are exceptions such as Pollux which is Beta Geminorum.

HIP91772 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD173740. The Gliese ID of the star is GL 725B. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

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

Location of Struve 2398 B

The location of the multiple star system in the night sky 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 object is compared to the celestial equator and is expressed in degrees. For Struve 2398 B, the location is 18h 42m 48.51 and +59° 37` 20.5 .

Radial Velocity and Proper Motion of Struve 2398 B

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 1,809.15 ± 3.04 miliarcseconds/year towards the north and -1,338.68 ± 3.21 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 the Sun is 1.09 km/s with an error of about 0.09 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties (Colour, Temperature) of Struve 2398 B

Struve 2398 B has a spectral type of K5. This means the star is a orange to red multiple star system. The star is 7,400.00 Parsecs from the Galactic Centre or in terms of Light Years is 24,136.09 s. The star has a B-V Colour Index of 1.56 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 3,878 Kelvin.

Struve 2398 B Radius has been calculated as being 0.08 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 58,083.76.km. If you need the diameter of the star, you just need to multiple the radius by 2. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 0.08. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is -0.51 with an error value of 0.05 Fe/H with the Sun has a value of 1 to put it into context.

Struve 2398 B Apparent and Absolute Magnitudes

Struve 2398 B has an apparent magnitude of 9.70 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 11.97 If you used the 2007 Parallax value, you would get an absolute magnitude of 12.01. 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 Struve 2398 B

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 284.48 which gave the calculated distance to Struve 2398 B as 11.47 light years away from Earth or 3.52 parsecs. It would take a spaceship travelling at the speed of light, 11.47 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 289.48 which put Struve 2398 B at a distance of 11.27 light years or 3.45 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.

Using the 2007 distance, the star is roughly 711,608.62 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun.

The star's Galacto-Centric Distance is 7,400.00 Parsecs or 24,136.09 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

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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Additional Struve 2398 B Facts and Figures

Visual Facts


Primary / Proper / Traditional NameStruve 2398 B
Alternative NamesHD 173740, HIP 91772, Gliese 725B
Spectral TypeK5
Constellation's Main StarNo
Multiple Star SystemYes
Star TypeMultiple Star System
ColourOrange to Red
GalaxyMilky Way
ConstellationDraco
Absolute Magnitude 11.97 / 12.01
Visual / Apparent Magnitude9.70
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)18h 42m 48.51
Declination (Dec.)+59° 37` 20.5
Galactic Latitude24.23 degrees
Galactic Longitude89.28 degrees
1997 Distance from Earth284.48 Parallax (milliarcseconds)
 11.47 Light Years
 3.52 Parsecs
2007 Distance from Earth289.48 Parallax (milliarcseconds)
 11.27 Light Years
 3.45 Parsecs
 711,608.62 Astronomical Units
Galacto-Centric Distance24,136.09 Light Years / 7,400.00 Parsecs
Proper Motion Dec.1809.15 ± 3.04 milliarcseconds/year
Proper Motion RA.-1338.68 ± 3.21 milliarcseconds/year
B-V Index1.56
Radial Velocity1.09 ± 0.09 km/s
Iron Abundance-0.51 ± 0.05 Fe/H
Eccentricity0.08
Semi-Major Axis7922.00
Associated / Clustered StarsStruve 2398

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)0.08
Effective Temperature3,878 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
173740B9.80000-1383.000001846.00000K5Orange1963
C12.800001926

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