Universe Guide


R Aquilae, HD177940, HIP93820

R Aquilae is a red pulsating star that can be located in the constellation of Aquila. The star can not be seen by the naked eye, you need a telescope to see it.

HIP93820 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD177940. The Id of the star in the Gould Star Catalogue is 22. Stars in the southern hemisphere are more likely to have a Gould Id than the northern hemisphere. For example, there are no Gould classified stars in Ursa Major.

R Aquilae has alternative name(s), R Aql.

Location of R Aquilae

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 R Aquilae, the location is 19h 06m 22.25 and +08d13`48.6 .

Proper Motion of R Aquilae

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 -67.01 ± 0.65 miliarcseconds/year towards the north and 3.79 ± 0.87 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of R Aquilae

R Aquilae has a spectral type of M5e-M9e. This means the star is a red star. The star has a B-V Colour Index of 1.13 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,702 Kelvin.

R Aquilae Radius has been calculated as being 8.96 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 6,234,662.65.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 17.88. 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 -1.00 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

R Aquilae Apparent and Absolute Magnitudes

R Aquilae has an apparent magnitude of 7.61 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 0.98 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.52. 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 R Aquilae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.73 which gave the calculated distance to R Aquilae as 689.56 light years away from Earth or 211.42 parsecs. It would take a spaceship travelling at the speed of light, 689.56 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 2.37 which put R Aquilae at a distance of 1376.22 light years or 421.94 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.

Variable Type of R Aquilae

The star is a pulsating Omicron Ceti 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. R Aquilae brightness ranges from a magnitude of 8.922 to a magnitude of 5.808 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 277.0 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.

R Aquilae Facts

Alternative Names

Traditional/Proper NameR Aquilae
Short NameR Aql
Hipparcos Library I.D.93820
Bonner DurchmusterungBD+08 3970
Gould I.D.22
Henry Draper Designation177940

Visual Facts

Star Type star
Absolute Magnitude0.98 / -0.52
Visual / Apparent Magnitude7.61
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)19h 06m 22.25
Declination (Dec.)+08d13`48.6
Galactic Latitude0.45 degrees
Galactic Longitude41.95 degrees
1997 Distance from Earth4.73 Parallax (milliarcseconds)
 689.56 Light Years
 211.42 Parsecs
2007 Revised Distance from Earth2.37 Parallax (milliarcseconds)
 1376.22 Light Years
 421.94 Parsecs
Proper Motion Dec.-67.01 ± 0.65 milliarcseconds/year
Proper Motion RA.3.79 ± 0.87 milliarcseconds/year
B-V Index1.13
Radial Velocity34.60 ± 0.60 km/s
Iron Abundance-1.00 ± 9.99 Fe/H
Spectral TypeM5e-M9e
Colour(M) Red

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeOmicron Ceti
Mean Variability Period in Days277.000
Variable Magnitude Range (Brighter - Dimmer)5.808 - 8.922

Estimated Facts

Calculated Effective Temperature4,702 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
177940+08 3970.0A-21.00000-89.00000M4Red
+08 3968.0C10.50000-6.00000-13.000001877

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