Universe Guide

281 G. Hydrae

281 G. Hydrae Facts

  • 281 G. Hydrae is a pulsating giant star that can be located in the constellation of Hydra. The description is based on the spectral class.
  • 281 G. Hydrae is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (K4/K5III) of the star, the star's colour is orange to 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 1169.04 light years away from us. Distance

281 G. Hydrae's Alternative Names

The Id of the star in the Yale Bright Star Catalogue is HR4420. HIP55953 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD99712.

281 G. Hydrae has alternative name(s) :- QT Hya, QT Hya.

The Gould star designation is one that was designed by American astronomer, Benjamin Apthorp Gould. Gould stars are predominantly in the Southern and Equatorial constellations but do appear in northern constellations such as Bootes and Orion. The star has the designation 281 G. Hydrae. There are no stars with a Gould designation in Ursa Major for example.

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

Location of 281 G. Hydrae

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 281 G. Hydrae, the location is 11h 27m 58.67 and -35° 19` 43.9 .

Radial Velocity and Proper Motion of 281 G. Hydrae

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 -0.31 ± 0.29 milliarcseconds/year towards the north and 9.81 ± 0.45 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 -17.80000 km/s with an error of about 2.30 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 281 G. Hydrae

281 G. Hydrae Colour and Temperature

Based on the star's spectral type of K4/K5III , 281 G. Hydrae's colour and type is orange to red giant star. The star has a B-V Colour Index of 1.61 which means the star's temperature is about 3,754 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

281 G. Hydrae Radius

281 G. Hydrae estimated radius has been calculated as being 44.05 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 30,648,838.45.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 40.731267652271680015421190082. 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.

281 G. Hydrae Apparent and Absolute Magnitudes

281 G. Hydrae has an apparent magnitude of 6.44 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 -1.50 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.33. 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 281 G. Hydrae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 2.58000 which gave the calculated distance to 281 G. Hydrae as 1264.20 light years away from Earth or 387.60 parsecs. If you want that in miles, it is about 7,431,758,196,778,719.76, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 2.79000 which put 281 G. Hydrae at a distance of 1169.04 light years or 358.42 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 73,928,916.71 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 7,329.00 Parsecs or 23,904.51 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 281 G. Hydrae

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 A3807361,065,187,043.43
Speed of Sound (Mach 1)767.2691,021,776,800.53
Concorde (Mach 2)1,534.54510,887,734.41
New Horizons Probe33,00023,756,898.91
Speed of Light670,616,629.001,169.04

Variable Type of 281 G. Hydrae

The star is a pulsating Semi-Regular Star w 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. 281 G. Hydrae brightness ranges from a magnitude of 6.583 to a magnitude of 6.519 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 100.2 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 281 G. Hydrae Facts and Figures

Visual Facts

Primary / Proper / Traditional Name281 G. Hydrae
Alternative NamesQT Hya, HD 99712, HIP 55953, HR 4420, QT Hya
Spectral TypeK4/K5III
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeGiant Star
ColourOrange to Red
GalaxyMilky Way
Absolute Magnitude -1.50 / -1.33
Visual / Apparent Magnitude6.44
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)11h 27m 58.67
Declination (Dec.)-35° 19` 43.9
Galactic Latitude24.50652326 degrees
Galactic Longitude284.30847739 degrees
1997 Distance from Earth2.58000 Parallax (milliarcseconds)
 1264.20 Light Years
 387.60 Parsecs
2007 Distance from Earth2.79000 Parallax (milliarcseconds)
 1169.04 Light Years
 358.42 Parsecs
 73,928,916.71 Astronomical Units
Galacto-Centric Distance23,904.51 Light Years / 7,329.00 Parsecs
Proper Motion Dec.-0.31000 ± 0.29000 milliarcseconds/year
Proper Motion RA.9.81000 ± 0.45000 milliarcseconds/year
B-V Index1.61
Radial Velocity-17.80000 ± 2.30 km/s
Semi-Major Axis10763.0000000

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeSemi-Regular Star w
Mean Variability Period in Days100.190
Variable Magnitude Range (Brighter - Dimmer)6.519 - 6.583

Estimated Calculated Facts

Radius (x the Sun)40.73
Effective Temperature3,754 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Comments and Questions

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