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Y Hydrae, HD85405, HIP48327

Y Hydrae is a carbon red pulsating variable star that can be located in the constellation of Hydra. The description is based on the spectral class. Y Hydrae is not part of the constellation but is within the borders of the constellation.

The star can not be seen by the naked eye, you need a telescope to see it.

Y Hydrae's Alternative Names

HIP48327 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD85405.

Y Hydrae has alternative name(s) :- , Y Hya.

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-22 2739.

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

Location of Y Hydrae

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 star is compared to the celestial equator and is expressed in degrees. For Y Hydrae, the location is 09h 51m 03.71 and -23° 01` 02.3 .

Radial Velocity and Proper Motion of Y Hydrae

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 -5.24 ± 0.35 miliarcseconds/year towards the north and 9.19 ± 0.45 miliarcseconds/year east if we saw them in the horizon.

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is 3.50 km/s with an error of about 1.60 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 (Colour, Temperature) of Y Hydrae

Y Hydrae has a spectral type of C. This means the star is a carbon red variable star. The star is 7,483.00 Parsecs from the Galactic Centre or terms of Light Years is 24,406.80 s. The star has a B-V Colour Index of 3.43 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 0 Kelvin. The star's Iron Abundance is -0.10 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Y Hydrae Apparent and Absolute Magnitudes

Y Hydrae has an apparent magnitude of 6.85 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 -0.86 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.10. 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 Y Hydrae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 2.87 which gave the calculated distance to Y Hydrae as 1136.46 light years away from Earth or 348.43 parsecs. It would take a spaceship travelling at the speed of light, 1136.46 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 2.57 which put Y Hydrae at a distance of 1269.12 light years or 389.11 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 80,259,139.51 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 7,483.00 Parsecs or 24,406.80 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Y Hydrae

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. Y Hydrae brightness ranges from a magnitude of 6.740 to a magnitude of 6.441 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.3 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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Y Hydrae Facts

Visual Facts


Primary / Proper / Traditional NameY Hydrae
Alternative NamesHD 85405, HIP 48327, BD-22 2739, Y Hya
Spectral TypeC
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeVariable Star
Colour carbon red
GalaxyMilky Way
ConstellationHydra
Absolute Magnitude -0.86 / -1.10
Visual / Apparent Magnitude6.85
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)09h 51m 03.71
Declination (Dec.)-23° 01` 02.3
Galactic Latitude23.58 degrees
Galactic Longitude257.60 degrees
1997 Distance from Earth2.87 Parallax (milliarcseconds)
 1136.46 Light Years
 348.43 Parsecs
2007 Distance from Earth2.57 Parallax (milliarcseconds)
 1269.12 Light Years
 389.11 Parsecs
 80,259,139.51 Astronomical Units
Galacto-Centric Distance24,406.80 Light Years / 7,483.00 Parsecs
Proper Motion Dec.-5.24 ± 0.35 milliarcseconds/year
Proper Motion RA.9.19 ± 0.45 milliarcseconds/year
B-V Index3.43
Radial Velocity3.50 ± 1.60 km/s
Iron Abundance-0.10 ± 9.99 Fe/H
Eccentricity0.22
Semi-Major Axis8361.00

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeSemiregular late- (M
Mean Variability Period in Days0.262
Variable Magnitude Range (Brighter - Dimmer)6.441 - 6.740

Estimated Facts


Sources and Links


SIMBAD SourceLink

Related Stars


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