Universe Guide

Alpha Octantis

Alpha Octantis Facts

  • Alpha Octantis is a eclipsing binary sys giant star that can be located in the constellation of Octans. The description is based on the spectral class.
  • Alpha Octantis is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (F4III) of the star, the star's colour is yellow to white .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • The star has an estimated age of 1.50 Billion of Years but could be as young as 1.40 to 1.60 according to Hipparcos.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 142.00 light years away from us. Distance

Alpha Octantis's Alternative Names

Alpha Octantis (Alf Oct) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.

The Id of the star in the Yale Bright Star Catalogue is HR8021. HIP104043 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD199532.

Alpha Octantis has alternative name(s) :- , alf Oct.

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

Location of Alpha Octantis

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 Alpha Octantis, the location is 21h 04m 43.03 and -77° 01` 22.3 .

Radial Velocity and Proper Motion of Alpha Octantis

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 -369.24 ± 0.17 milliarcseconds/year towards the north and 12.74 ± 0.23 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 85.90000 km/s with an error of about 1.50 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 Alpha Octantis

Alpha Octantis Colour and Temperature

Based on the star's spectral type of F4III , Alpha Octantis's colour and type is yellow to white giant star. The star has a B-V Colour Index of 0.49 which means the star's temperature is about 6,327 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

Alpha Octantis 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 14.48 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Alpha Octantis Radius

Alpha Octantis estimated radius has been calculated as being 3.32 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,306,609.09.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 3.1804508676151757123721010588. 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.

Alpha Octantis Iron Abundance

Alpha Octantis Iron Abundance is 0.14 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context. The value comes from the Hipparcos Extended Catalog.

Alpha Octantis Estimated Age

The stars age according to Hipparcos data files put the star at an age of about 1.50 Billion years old but could be between 1.40 and 1.60 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

Alpha Octantis Apparent and Absolute Magnitudes

Alpha Octantis has an apparent magnitude of 5.13 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 1.85 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.94. 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 Alpha Octantis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 22.07000 which gave the calculated distance to Alpha Octantis as 147.79 light years away from Earth or 45.31 parsecs. If you want that in miles, it is about 868,802,043,902,805.72, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 22.97000 which put Alpha Octantis at a distance of 142.00 light years or 43.54 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 8,980,707.09 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 7,374.00 Parsecs or 24,051.28 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 Alpha Octantis

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 A380736129,385,273.53
Speed of Sound (Mach 1)767.269124,112,353.45
Concorde (Mach 2)1,534.5462,056,095.85
New Horizons Probe33,0002,885,683.68
Speed of Light670,616,629.00142.00

Variable Type of Alpha Octantis

The star is a eclipsing binary sys Beta Lyrae (Sheliak) 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. Alpha Octantis brightness ranges from a magnitude of 5.260 to a magnitude of 5.221 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 2.9 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 Alpha Octantis Facts and Figures

Visual Facts

Primary / Proper / Traditional NameAlpha Octantis
Alternative NamesAlf Oct, HD 199532, HIP 104043, HR 8021, alf Oct
Spectral TypeF4III
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeGiant Star
ColourYellow - White
GalaxyMilky Way
Age1.50 Billion Years Old
Age Range1.40 - 1.60 Billion Years Old
Absolute Magnitude 1.85 / 1.94
Visual / Apparent Magnitude5.13
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)21h 04m 43.03
Declination (Dec.)-77° 01` 22.3
Galactic Latitude-33.65025989 degrees
Galactic Longitude315.95952763 degrees
1997 Distance from Earth22.07000 Parallax (milliarcseconds)
 147.79 Light Years
 45.31 Parsecs
2007 Distance from Earth22.97000 Parallax (milliarcseconds)
 142.00 Light Years
 43.54 Parsecs
 8,980,707.09 Astronomical Units
Galacto-Centric Distance24,051.28 Light Years / 7,374.00 Parsecs
Proper Motion Dec.-369.24000 ± 0.17000 milliarcseconds/year
Proper Motion RA.12.74000 ± 0.23000 milliarcseconds/year
B-V Index0.49
Radial Velocity85.90000 ± 1.50 km/s
Iron Abundance0.1400 ± 9.99 Fe/H
Semi-Major Axis3072.0000000
Stellar Luminosity (Lsun)14.4800000

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassEclipsing binary sys
Variable Star TypeBeta Lyrae (Sheliak)
Mean Variability Period in Days2.877
Variable Magnitude Range (Brighter - Dimmer)5.221 - 5.260

Estimated Calculated Facts

Radius (x the Sun)3.18
Effective Temperature6,327 Kelvin

Sources and Links

SIMBAD SourceLink

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