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Pennae Caudalis (Pi2 Cygni, 81 Cygni) Star Facts

Pennae Caudalis Facts

  • Pennae Caudalis is a giant star that can be located in the constellation of Cygnus. The description is based on the spectral class.
  • Pennae Caudalis is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (B3III) of the star, the star's colour is blue .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 1105.64 light years away from us. Distance

Pennae Caudalis's Alternative Names

Pi2 Cygni (Pi.02 Cyg) 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 HR8335. HIP107533 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD207330.

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 81 Cygni. The Flamsteed name can be shortened to 81 Cyg.

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+48 3504.

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

Location of Pennae Caudalis

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 Pennae Caudalis, the location is 21h 46m 47.61 and +49° 18` 34.5 .

Radial Velocity and Proper Motion of Pennae Caudalis

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 -2.00 ± 0.27 milliarcseconds/year towards the north and 2.77 ± 0.34 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 -12.30000 km/s with an error of about 7.40 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 Pennae Caudalis

Pennae Caudalis Temperature and Colour

Based on the star's spectral type of B3III , Pennae Caudalis's colour and type is blue giant star. The star has a B-V Colour Index of -0.12 which means the star's temperature is about 12,367 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

Pennae Caudalis 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 3,892.42 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Pennae Caudalis Radius

Pennae Caudalis estimated radius has been calculated as being 10.29 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 7,159,680.90.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 9.826712728600874685401114292. 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.

Pennae Caudalis Iron Abundance

Pennae Caudalis Iron Abundance is -0.02 with an error value of 0.04 Fe/H with the Sun has a value of 1 to put it into context. The value comes from the Hipparcos Extended Catalog.

Pennae Caudalis Apparent and Absolute Magnitudes

Pennae Caudalis has an apparent magnitude of 4.23 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 -3.52 If you used the 2007 Parallax value, you would get an absolute magnitude of -3.42. 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 Pennae Caudalis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 2.82000 which gave the calculated distance to Pennae Caudalis as 1156.61 light years away from Earth or 354.61 parsecs. If you want that in miles, it is about 6,799,276,892,877,895.16, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 2.95000 which put Pennae Caudalis at a distance of 1105.64 light years or 338.98 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 69,919,156.82 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 7,436.00 Parsecs or 24,253.51 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 Pennae Caudalis

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)
Walking4185,365,142,421.89
Car1206,178,838,080.73
Airbus A3807361,007,419,252.29
Speed of Sound (Mach 1)767.269966,363,256.81
Concorde (Mach 2)1,534.54483,180,998.66
New Horizons Probe33,00022,468,502.11
Speed of Light670,616,629.001,105.64

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 Pennae Caudalis Facts and Figures

Visual Facts


Primary / Proper / Traditional NamePennae Caudalis
Alternative NamesPi2 Cygni, Pi.02 Cyg, HD 207330, HIP 107533, HR 8335, 81 Cygni, 81 Cyg, BD+48 3504
Spectral TypeB3III
Constellation's Main StarNo
Multiple Star SystemYes
Star TypeGiant Star
ColourBlue
GalaxyMilky Way
ConstellationCygnus
Absolute Magnitude -3.52 / -3.42
Visual / Apparent Magnitude4.23
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)21h 46m 47.61
Declination (Dec.)+49° 18` 34.5
Galactic Latitude-3.21893553 degrees
Galactic Longitude94.83242794 degrees
1997 Distance from Earth2.82000 Parallax (milliarcseconds)
 1156.61 Light Years
 354.61 Parsecs
2007 Distance from Earth2.95000 Parallax (milliarcseconds)
 1105.64 Light Years
 338.98 Parsecs
 69,919,156.82 Astronomical Units
Galacto-Centric Distance24,253.51 Light Years / 7,436.00 Parsecs
Proper Motion Dec.-2.00000 ± 0.27000 milliarcseconds/year
Proper Motion RA.2.77000 ± 0.34000 milliarcseconds/year
B-V Index-0.12
Radial Velocity-12.30000 ± 7.40 km/s
Iron Abundance-0.0200 ± 0.04 Fe/H
Eccentricity0.03420
Semi-Major Axis7646.0000000
Stellar Luminosity (Lsun)3892.4200000
Associated / Clustered StarsAzelfafage

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)9.83
Effective Temperature12,367 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
207330+48 3504.0A4.400004.00000-2.00000B3Blue/White
B6.000004.00000-2.000001991

Location of Pennae Caudalis in Cygnus


Pennae Caudalis Location in Cygnus

The map was generated using Night Vision, an awesome free application by Brian Simpson.

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