Universe Guide

Tau4 Serpentis (17 Serpentis) Star Facts

Tau4 Serpentis Facts

  • Tau4 Serpentis is a pulsating giant star that can be located in the constellation of Serpens. The description is based on the spectral class.
  • Tau4 Serpentis is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (M5II-III) of the star, the star's colour is 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 671.12 light years away from us. Distance

Tau4 Serpentis's Alternative Names

Tau4 Serpentis (Tau04 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.

HIP76423 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD139216.

Tau4 Serpentis has alternative name(s) :- , tau04 Ser.

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 17 Serpentis. The Flamsteed name can be shortened to 17 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 2890.

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

Location of Tau4 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 Tau4 Serpentis, the location is 15h 36m 28.19 and +15° 06` 05.0 .

Radial Velocity and Proper Motion of Tau4 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 8.89 ± 0.33 milliarcseconds/year towards the north and -3.66 ± 0.46 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 -27.11000 km/s with an error of about 0.72 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 Tau4 Serpentis

Tau4 Serpentis Colour and Temperature

Based on the star's spectral type of M5II-III , Tau4 Serpentis's colour and type is red giant star. The star has a B-V Colour Index of 1.2 which means the star's temperature is about 4,489 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

Tau4 Serpentis 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 155.25 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Tau4 Serpentis Radius

Tau4 Serpentis estimated radius has been calculated as being 12.26 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 8,532,645.66.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 15.871017994887867319875128427. 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.

Tau4 Serpentis Apparent and Absolute Magnitudes

Tau4 Serpentis has an apparent magnitude of 6.51 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 0.50 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.06. 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 Tau4 Serpentis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 6.27000 which gave the calculated distance to Tau4 Serpentis as 520.20 light years away from Earth or 159.49 parsecs. If you want that in miles, it is about 3,058,060,919,130,113.92, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 4.86000 which put Tau4 Serpentis at a distance of 671.12 light years or 205.76 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 42,440,750.80 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 7,282.00 Parsecs or 23,751.21 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 Tau4 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)
Airbus A380736611,500,315.29
Speed of Sound (Mach 1)767.269586,579,455.26
Concorde (Mach 2)1,534.54293,289,345.38
New Horizons Probe33,00013,638,310.06
Speed of Light670,616,629.00671.12

Variable Type of Tau4 Serpentis

The star is a pulsating Semiregular late- (M 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. Tau4 Serpentis brightness ranges from a magnitude of 6.397 to a magnitude of 6.052 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.4 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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Additional Tau4 Serpentis Facts and Figures

Visual Facts

Primary / Proper / Traditional NameTau4 Serpentis
Alternative NamesTau04 Ser, HD 139216, HIP 76423, 17 Serpentis, 17 Ser, BD+15 2890, tau04 Ser
Spectral TypeM5II-III
Constellation's Main StarNo
Multiple Star SystemYes
Star TypeGiant Star
GalaxyMilky Way
Absolute Magnitude 0.50 / -0.06
Visual / Apparent Magnitude6.51
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)15h 36m 28.19
Declination (Dec.)+15° 06` 05.0
Galactic Latitude49.88375035 degrees
Galactic Longitude24.08644474 degrees
1997 Distance from Earth6.27000 Parallax (milliarcseconds)
 520.20 Light Years
 159.49 Parsecs
2007 Distance from Earth4.86000 Parallax (milliarcseconds)
 671.12 Light Years
 205.76 Parsecs
 42,440,750.80 Astronomical Units
Galacto-Centric Distance23,751.21 Light Years / 7,282.00 Parsecs
Proper Motion Dec.8.89000 ± 0.33000 milliarcseconds/year
Proper Motion RA.-3.66000 ± 0.46000 milliarcseconds/year
B-V Index1.2
Radial Velocity-27.11000 ± 0.72 km/s
Semi-Major Axis7988.0000000
Stellar Luminosity (Lsun)155.2500000
Associated / Clustered StarsTau1 Serpentis
Tau2 Serpentis
Tau3 Serpentis
Tau5 Serpentis
Tau6 Serpentis
Tau8 Serpentis

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeSemiregular late- (M
Mean Variability Period in Days0.353
Variable Magnitude Range (Brighter - Dimmer)6.052 - 6.397

Estimated Calculated Facts

Radius (x the Sun)15.87
Effective Temperature4,489 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

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