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Caput Trianguli, Alpha Trianguli, 2 Trianguli, HD11443, HIP8796, HR544

Caput Trianguli (Alpha Trianguli) is a blue to white subgiant star that can be located in the constellation of Triangulum. Caput Trianguli is the brightest star in Triangulum based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it. The star has an estimated age of 1.60 Billion of Years but could be as young as 1.50 to 1.70 according to Hipparcos.

Alpha Trianguli is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR544. HIP8796 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD11443. The Gliese ID of the star is Gliese GL78.1. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Ref : Star Names.

Caput Trianguli has alternative name(s), Mothallah, Metallah, Ras al Mothallah, Elmuthalleth, Caput Trianguli , alf Tri.

Location of Caput Trianguli

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 Caput Trianguli, the location is 01h 53m 04.90 and +29d34`45.8 .

Proper Motion of Caput Trianguli

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 -234.24 ± 0.13 miliarcseconds/year towards the north and 10.82 ± 0.23 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Age, Radius) of Caput Trianguli

Caput Trianguli has a spectral type of F6IV. This means the star is a blue to white subgiant star. The star is 7412.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24175.2270572800000000s. The star has a B-V Colour Index of 0.48 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,369 Kelvin.

Caput Trianguli Radius has been calculated as being 3.12 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,173,833.05.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 3.08. 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 0.02 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

The stars age according to Hipparcos data files put the star at an age of about 1.60 Billion years old but could be between 1.50 and 1.70 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

Caput Trianguli Apparent and Absolute Magnitudes

Caput Trianguli has an apparent magnitude of 3.42 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 1.95 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.98. 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 Caput Trianguli

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 50.87 which gave the calculated distance to Caput Trianguli as 64.12 light years away from Earth or 19.66 parsecs. It would take a spaceship travelling at the speed of light, 64.12 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 51.50 which put Caput Trianguli at a distance of 63.33 light years or 19.42 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.

The star's Galacto-Centric Distance is 7,412.00 Parsecs or 24,175.23 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*. Caput Trianguli brightness ranges from a magnitude of 3.526 to a magnitude of 3.516 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.9 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.

Caput Trianguli Facts

Alternative Names

Traditional/Proper NameCaput Trianguli
Flamsteed Name2 Trianguli
Flamsteed Short Name2 Tri
Short Namealf Tri
Bayer DesignationAlpha Trianguli
Alternative Name(s)Mothallah, Metallah, Ras al Mothallah, Elmuthalleth, Caput Trianguli
Hipparcos Library I.D.8796
Yale Bright Star Catalogue (HR) Id544
Bonner DurchmusterungBD+28 312
Gliese ID78.1
Henry Draper Designation11443

Visual Facts

Star Typesubgiant star
Age1.60 Billion Years Old
Age Range1.50 - 1.70 Billion Years Old
Absolute Magnitude1.95 / 1.98
Visual / Apparent Magnitude3.42
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)01h 53m 04.90
Declination (Dec.)+29d34`45.8
Galactic Latitude-31.40 degrees
Galactic Longitude138.64 degrees
1997 Distance from Earth50.87 Parallax (milliarcseconds)
 64.12 Light Years
 19.66 Parsecs
2007 Revised Distance from Earth51.50 Parallax (milliarcseconds)
 63.33 Light Years
 19.42 Parsecs
Galacto-Centric Distance24,175.23 Light Years / 7,412.00 Parsecs
Proper Motion Dec.-234.24 ± 0.13 milliarcseconds/year
Proper Motion RA.10.82 ± 0.23 milliarcseconds/year
B-V Index0.48
Radial Velocity-12.10 ± 3.10 km/s
Iron Abundance0.02 ± 9.99 Fe/H
Spectral TypeF6IV
Colour(F) blue to white

Variable Star Details

Mean Variability Period in Days0.868
Variable Magnitude Range (Brighter - Dimmer)3.516 - 3.526

Estimated Facts

Calculated Effective Temperature6,369 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

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
11443+28 312.0A3.6000011.00000-230.00000F5Yellow/White
B12.900001909
C12.200001909

Location of Caput Trianguli in Triangulum


Caput Trianguli (Alpha Trianguli) Location in Triangulum

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


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