Universe Guide


Zosma (Delta Leonis) - HD97603 - HIP54872 - HR4357

Zosma (Delta Leonis) is a blue main sequence dwarf star that can be located in the constellation of Leo. Delta Leonis is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR4357. HIP54872 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD97603. Zosma has alternative name(s), Duhr,68 Leonis , 68 Leo.

Zosma is one of the brightest stars in the constellation of Leo. It is about 2.2x, or read it another way, twice as big as the Sun. Its name is Arabic for Girdle from where it gets its name from, i.e. its location in the constellation. It is one of the brightest in the night sky compared to the other stars but is not the brightest in Leo, that honour goes to Regulus. As it is travelling through the galaxy at a speed of 26.6km/s relative to the Sun, it will come close to the Sun in about 518,000 years when it will brighten in the night sky but not any where near as the Sun or Moon. 1

Although Zosma is fourth brightest evident by the fact it is Delta, the fourth letter of the Greek constellation, it is brighter than the third star, Algieba which is a double star. Zosma is brighter than both stars but it falls in the pecking order because the sum of the brightness of the two Algieba stars is brighter than Zosma. It is a dying star and is over halway through its dying process.2

Location of Zosma

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 Zosma, the location is 11h 14m 06.41 and +20d31`26.5 .

Proper Motion of Zosma

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 -129.88 ± 000.15 towards the north and 143.42 ± 000.25 east if we saw them in the horizon.

Zosma 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 12.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of Zosma

Zosma has a spectral type of A4V. This means the star is a blue main sequence dwarf star. The star has a B-V Colour Index of 0.12 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 8,298 Kelvin.

Zosma has been calculated as 2.46 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,711,701.42.km.

Zosma Apparent and Absolute Magnitudes

Zosma has an apparent magnitude of 2.56 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 1.32 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.29. 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 Zosma

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 56.52 which gave the calculated distance to Zosma as 57.71 light years away from Earth or 17.69 parsecs. It would take a spaceship travelling at the speed of light, 57.71 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 55.82 which put Zosma at a distance of 58.43 light years or 17.91 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.

Meteor Showers Radiating from near Zosma

The Delta Leonids Meteor Shower radiants from a point near this star. The meteor shower runs typically between Feb 15 - Mar 10 with a peak date of Feb 25. The speed of a meteor in the shower is 23 Km/s. The amount of meteors predicted to be seen per hour (Zenith Hourly Rate) is 23.

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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

Zosma Facts

Alternative Names

Traditional NameZosma
Short Name68 Leo
Bayer DesignationDelta Leonis
Alternative Name(s)Duhr,68 Leonis
Hipparcos Library I.D.54872
Yale Bright Star Catalogue (HR) Id4357
Bonner DurchmusterungBD+21 2298
Henry Draper Designation97603

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude1.32 / 1.29
Apparent Magnitude2.56
Right Ascension (R.A.)11h 14m 06.41
Declination (Dec.)+20d31`26.5
1997 Distance from Earth56.52 Parallax (milliarcseconds)
 57.71 Light Years
 17.69 Parsecs
2007 Revised Distance from Earth55.82 Parallax (milliarcseconds)
 58.43 Light Years
 17.91 Parsecs
Proper Motion Dec.-129.88 ± 0.15 milliarcseconds/year
Proper Motion RA.143.42 ± 0.25 milliarcseconds/year
B-V Index0.12
Spectral TypeA4V
Colour(A) blue

Estimated Facts

Radius (x the Sun)2.46
Luminosity (x the Sun)12.0000000
Calculated Effective Temperature8,298 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
97603+21 2298.0A2.60000142.00000-135.00000A3White

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