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Tau1 Serpentis (9 Serpentis) Star Facts

Tau1 Serpentis Facts

  • Tau1 Serpentis is a giant star that can be located in the constellation of Serpens. The description is based on the spectral class.
  • Tau1 Serpentis is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (M1III) of the star, the star's colour is red .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 689.56 light years away from us. Distance

Tau1 Serpentis's Alternative Names

Tau1 Serpentis (Tau01 Ser) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.

The Id of the star in the Yale Bright Star Catalogue is HR5739. HIP75530 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD137471.

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 9 Serpentis. The Flamsteed name can be shortened to 9 Ser.

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+15 2858.

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

Location of Tau1 Serpentis

The location of the giant 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 Tau1 Serpentis, the location is 15h 25m 47.41 and +15° 25` 41.0 .

Radial Velocity and Proper Motion of Tau1 Serpentis

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 -7.41 ± 0.21 milliarcseconds/year towards the north and -12.52 ± 0.35 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 -16.51000 km/s with an error of about 0.23 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 Tau1 Serpentis

Tau1 Serpentis Temperature and Colour

Based on the star's spectral type of M1III , Tau1 Serpentis's colour and type is red giant star. The star has a B-V Colour Index of 1.65 which means the star's temperature is about 3,640 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

Tau1 Serpentis Radius

Tau1 Serpentis estimated radius has been calculated as being 61.48 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 42,776,532.91.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 46.2077764298717322468478792. 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.

Tau1 Serpentis Apparent and Absolute Magnitudes

Tau1 Serpentis has an apparent magnitude of 5.16 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 -2.09 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.47. 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 Tau1 Serpentis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 3.55000 which gave the calculated distance to Tau1 Serpentis as 918.77 light years away from Earth or 281.69 parsecs. If you want that in miles, it is about 5,401,104,634,119,905.36, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 4.73000 which put Tau1 Serpentis at a distance of 689.56 light years or 211.42 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 43,608,201.47 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 7,284.00 Parsecs or 23,757.74 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 Tau1 Serpentis

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)
Walking4115,607,600,673.31
Car1203,853,586,689.11
Airbus A380736628,302,177.57
Speed of Sound (Mach 1)767.269602,696,580.59
Concorde (Mach 2)1,534.54301,347,897.54
New Horizons Probe33,00014,013,042.51
Speed of Light670,616,629.00689.56

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 Tau1 Serpentis Facts and Figures

Visual Facts


Primary / Proper / Traditional NameTau1 Serpentis
Alternative NamesTau01 Ser, HD 137471, HIP 75530, HR 5739, 9 Serpentis, 9 Ser, BD+15 2858
Spectral TypeM1III
Constellation's Main StarNo
Multiple Star SystemYes
Star TypeGiant Star
ColourRed
GalaxyMilky Way
ConstellationSerpens
Absolute Magnitude -2.09 / -1.47
Visual / Apparent Magnitude5.16
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)15h 25m 47.41
Declination (Dec.)+15° 25` 41.0
Galactic Latitude52.36308663 degrees
Galactic Longitude22.85803300 degrees
1997 Distance from Earth3.55000 Parallax (milliarcseconds)
 918.77 Light Years
 281.69 Parsecs
2007 Distance from Earth4.73000 Parallax (milliarcseconds)
 689.56 Light Years
 211.42 Parsecs
 43,608,201.47 Astronomical Units
Galacto-Centric Distance23,757.74 Light Years / 7,284.00 Parsecs
Proper Motion Dec.-7.41000 ± 0.21000 milliarcseconds/year
Proper Motion RA.-12.52000 ± 0.35000 milliarcseconds/year
B-V Index1.65
Radial Velocity-16.51000 ± 0.23 km/s
Eccentricity0.04420
Semi-Major Axis6974.0000000
Associated / Clustered StarsTau2 Serpentis
Tau3 Serpentis
Tau4 Serpentis
Tau5 Serpentis
Tau6 Serpentis
Tau8 Serpentis

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)46.21
Effective Temperature3,640 Kelvin

Sources and Links


SIMBAD SourceLink

Related Stars


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