Universe Guide

HD 154021 (28 Ophiuchi)

HD 154021 Facts

  • HD 154021 is a subgiant star that can be located in the constellation of Ophiuchus. The description is based on the spectral class.
  • HD 154021 is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (B9IV/V) of the star, the star's colour is blue .
  • The star can not be seen by the naked eye, you need a telescope to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 492.69 light years away from us. Distance

HD 154021's Alternative Names

HIP83508 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD154021.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 28 Ophiuchi. The Flamsteed name can be shortened to 28 Oph.

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

Location of HD 154021

The location of the subgiant 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 HD 154021, the location is 17h 04m 00.82 and -25° 41` 52.6 .

Proper Motion of HD 154021

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 -23.12 ± 0.35 milliarcseconds/year towards the north and -6.96 ± 0.61 milliarcseconds/year east if we saw them in the horizon. . 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 HD 154021

HD 154021 Temperature and Colour

Based on the star's spectral type of B9IV/V , HD 154021's colour and type is blue subgiant star. The star has a B-V Colour Index of -0.08 which means the star's temperature is about 11,099 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

HD 154021 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 68.72 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

HD 154021 Radius

HD 154021 estimated radius has been calculated as being 2.21 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,537,507.63.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 1.7796239495346605203890728359. 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.

HD 154021 Apparent and Absolute Magnitudes

HD 154021 has an apparent magnitude of 6.66 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 0.29 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.76. 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 HD 154021

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 5.32000 which gave the calculated distance to HD 154021 as 613.09 light years away from Earth or 187.97 parsecs. If you want that in miles, it is about 3,604,126,430,045,139.45, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 6.62000 which put HD 154021 at a distance of 492.69 light years or 151.06 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 31,158,144.52 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 7,253.00 Parsecs or 23,656.63 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 HD 154021

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 A380736448,921,340.95
Speed of Sound (Mach 1)767.269430,626,164.93
Concorde (Mach 2)1,534.54215,312,801.84
New Horizons Probe33,00010,012,306.27
Speed of Light670,616,629.00492.69

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 HD 154021 Facts and Figures

Visual Facts

Primary / Proper / Traditional NameHD 154021
Alternative NamesHD 154021, HIP 83508, 28 Ophiuchi, 28 Oph
Spectral TypeB9IV/V
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeSubgiant Star
GalaxyMilky Way
Absolute Magnitude 0.29 / 0.76
Visual / Apparent Magnitude6.66
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)17h 04m 00.82
Declination (Dec.)-25° 41` 52.6
Galactic Latitude9.47168101 degrees
Galactic Longitude357.52081566 degrees
1997 Distance from Earth5.32000 Parallax (milliarcseconds)
 613.09 Light Years
 187.97 Parsecs
2007 Distance from Earth6.62000 Parallax (milliarcseconds)
 492.69 Light Years
 151.06 Parsecs
 31,158,144.52 Astronomical Units
Galacto-Centric Distance23,656.63 Light Years / 7,253.00 Parsecs
Proper Motion Dec.-23.12000 ± 0.35000 milliarcseconds/year
Proper Motion RA.-6.96000 ± 0.61000 milliarcseconds/year
B-V Index-0.08
Stellar Luminosity (Lsun)68.7200000

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Estimated Calculated Facts

Radius (x the Sun)1.78
Effective Temperature11,099 Kelvin

Sources and Links

SIMBAD SourceLink

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