Universe Guide

21 Sextantis

21 Sextantis Facts

  • 21 Sextantis is a star that can be located in the constellation of Sextans. The description is based on the spectral class.
  • 21 Sextantis is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (K0) of the star, the star's colour is orange to red .
  • The star can not be seen by the naked eye, you need a telescope to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 834.18 light years away from us. Distance

21 Sextantis's Alternative Names

HIP50140 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD88764.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 21 Sextantis. The Flamsteed name can be shortened to 21 Sex.

BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD-07 2989.

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

Location of 21 Sextantis

The location of the star 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 21 Sextantis, the location is 10h 14m 08.41 and -07° 59` 36.4 .

Radial Velocity and Proper Motion of 21 Sextantis

Proper Motion

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 -21.81 ± 0.35 milliarcseconds/year towards the north and -11.78 ± 0.54 milliarcseconds/year east if we saw them in the horizon.

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is 9.30000 km/s with an error of about 3.00 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 of 21 Sextantis

21 Sextantis Temperature and Colour

Based on the star's spectral type of K0 , 21 Sextantis's colour and type is orange to red star. The star has a B-V Colour Index of 1.03 which means the star's temperature is about 4,908 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

21 Sextantis 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 127.52 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

21 Sextantis Radius

21 Sextantis estimated radius has been calculated as being 10.79 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 7,508,875.32.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 13.338131196972998651087737103. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It has been known to produce widely incorrect figures.

21 Sextantis Apparent and Absolute Magnitudes

21 Sextantis has an apparent magnitude of 6.97 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 0.39 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.07. 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 21 Sextantis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.83000 which gave the calculated distance to 21 Sextantis as 675.29 light years away from Earth or 207.04 parsecs. If you want that in miles, it is about 3,969,776,928,257,160.00, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 3.91000 which put 21 Sextantis at a distance of 834.18 light years or 255.75 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 52,751,856.62 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 7,471.00 Parsecs or 24,367.66 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Travel Time to 21 Sextantis

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

DescriptionSpeed (m.p.h.)Time (years)
Airbus A380736760,074,700.52
Speed of Sound (Mach 1)767.269729,098,894.36
Concorde (Mach 2)1,534.54364,548,972.06
New Horizons Probe33,00016,951,969.08
Speed of Light670,616,629.00834.18

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 21 Sextantis Facts and Figures

Visual Facts

Primary / Proper / Traditional Name21 Sextantis
Alternative NamesHD 88764, HIP 50140, 21 Sex, BD-07 2989
Spectral TypeK0
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeStar
ColourOrange to Red
GalaxyMilky Way
Absolute Magnitude 0.39 / -0.07
Visual / Apparent Magnitude6.97
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)10h 14m 08.41
Declination (Dec.)-07° 59` 36.4
Galactic Latitude38.19718362 degrees
Galactic Longitude249.94204910 degrees
1997 Distance from Earth4.83000 Parallax (milliarcseconds)
 675.29 Light Years
 207.04 Parsecs
2007 Distance from Earth3.91000 Parallax (milliarcseconds)
 834.18 Light Years
 255.75 Parsecs
 52,751,856.62 Astronomical Units
Galacto-Centric Distance24,367.66 Light Years / 7,471.00 Parsecs
Proper Motion Dec.-21.81000 ± 0.35000 milliarcseconds/year
Proper Motion RA.-11.78000 ± 0.54000 milliarcseconds/year
B-V Index1.03
Radial Velocity9.30000 ± 3.00 km/s
Semi-Major Axis6776.0000000
Stellar Luminosity (Lsun)127.5200000

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Estimated Calculated Facts

Radius (x the Sun)13.34
Effective Temperature4,908 Kelvin

Sources and Links

SIMBAD SourceLink

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