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Zosma, Delta Leonis, 68 Leonis, HD97603, HIP54872, HR4357

Zosma (Delta Leonis) Location in Leo

Zosma (Delta Leonis) is a blue main sequence dwarf star that can be located in the constellation of Leo. The description is based on the spectral class. Zosma is a main star of the constellation.

The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

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 half way through its dying process.2

Zosma's Alternative Names

Delta Leonis (Del Leo) 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. The Gliese ID of the star is GL 419. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

Zosma has alternative name(s) :- Duhr.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 68 Leonis with it shortened to 68 Leo.

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+21 2298.

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

Location of Zosma

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 Zosma, the location is 11h 14m 06.41 and +20° 31` 26.5 .

Radial Velocity and 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 ± 0.15 miliarcseconds/year towards the north and 143.42 ± 0.25 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 -20.90 km/s with an error of about 0.60 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.

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

Physical Properties (Colour, Temperature) of Zosma

Zosma has a spectral type of A4V. This means the star is a blue main sequence dwarf star. The star is 7,405.00 Parsecs from the Galactic Centre or terms of Light Years is 24,152.40 s. 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 Radius has been calculated as being 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. 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 2.49. 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 -0.18 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

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.

Using the 2007 distance, the star is roughly 3,694,176.94 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 7,405.00 Parsecs or 24,152.40 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

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

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Zosma Facts

Visual Facts


Primary / Proper / Traditional NameZosma
Alternative NamesDelta Leonis, Del Leo, Duhr, HD 97603, HIP 54872, HR 4357, 68 Leonis, 68 Leo, BD+21 2298, Gliese 419
Spectral TypeA4V
Constellation's Main StarYes
Multiple Star SystemYes
Star Type main sequence Dwarf Star
Colour blue
GalaxyMilky Way
ConstellationLeo
Absolute Magnitude 1.32 / 1.29
Visual / Apparent Magnitude2.56
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)11h 14m 06.41
Declination (Dec.)+20° 31` 26.5
Galactic Latitude66.83 degrees
Galactic Longitude224.23 degrees
1997 Distance from Earth56.52 Parallax (milliarcseconds)
 57.71 Light Years
 17.69 Parsecs
2007 Distance from Earth55.82 Parallax (milliarcseconds)
 58.43 Light Years
 17.91 Parsecs
 3,694,176.94 Astronomical Units
Galacto-Centric Distance24,152.40 Light Years / 7,405.00 Parsecs
Proper Motion Dec.-129.88 ± 0.15 milliarcseconds/year
Proper Motion RA.143.42 ± 0.25 milliarcseconds/year
B-V Index0.12
Radial Velocity-20.90 ± 0.60 km/s
Iron Abundance-0.18 ± 9.99 Fe/H
Eccentricity0.23
Semi-Major Axis8718.00
Stellar Luminosity (Lsun)25.61

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Facts


Calculated Effective Temperature8,298 Kelvin

Sources and Links


SIMBAD SourceLink

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
B8.600001924
P12.100001879

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