The Astrogators' Guide to
Gamma Virginis
Location in Space
Radial Distance: based on a parallax of 0.08453
" 0.00118 arcseconds, we calculate the distance as1. 38.59 lightyears
± 0.539 lightyear.2. 2,440,140 AU
± 34070 AU.Equatorial Coordinates:
Right Ascension; 12 hr, 41 min, 39.6423 sec -3.7667t sec
Declination; -01 deg, 26 min, 57.75 sec +1.2t sec.
[elapsed time measured in centuries, Jan 2000 is t = 0]
Imagine standing on the north side of a plane in which Earth
's equator lies with the north celestial pole directly overhead and look toward the First Point of Aries (now in Pisces just southeast of the Circlet). Then look eastward (to the left) by 190 degrees and a little less than half a degree and then look south (down) by a little less than one and a half degrees.Ecliptic Coordinates:
Ecliptic Latitude; +2.7902896 degrees.
Ecliptic Longitude; 190.1414577 degrees.
Look toward the First Point of Aries (the point on the sky that the sun occupies on the first day of spring), shift your gaze eastward along the Ecliptic (the line that the sun traces through the Zodiac in the course of a year) by slightly more than 190 degrees, and then shift your gaze northward (+) by a little over two and three-quarters degrees along a line perpendicular to the Ecliptic.
Galactic Coordinates:
Galactic Latitude; +61.3256 degrees.
Galactic Longitude; 297.8343 degrees.
Look toward the radio source Sagittarius-A, move your gaze in an easterly direction along the plane of the Milky Way by almost 298 degrees, and then tilt your gaze by sixty-one and one-third degrees in a northerly direction at right angles to the plane of the Milky Way.
Annual Proper Motion
in Right Ascension = -0.565 arcsecond per year (6.684 AU per yr).
in Declination = +0.012 arcsecond per year (0.142 AU per yr).
Total proper motion = 0.56513 arcsecond per year in the direction 271.22 degrees counterclockwise from due celestial north.
in Parallax = -19.8±
0.9 kilometers per second (4.1768 AU per yr)Total motion = 7.883 AU per year = 37.369 kilometers per second.
From the present in 164,000 years Gamma Virginis will reach its perihelion 32.728 lightyears (2,069,000 AU) from Sol in the middle part of the constellation of Sextans.
Orientation in Space
Orbit size: the general orbit'
s semi-major axis (42.36 AU), the sum of the semi-major axes of the two stars' orbits, in AU (e=0.8781± 0.0025); varies between 5.16 AU and 79.56 AU.We refer the following to the plane of the sky, which we define as the plane comprising all straight lines that cross our line of sight through the barycenter of the system under study and that pass through that barycenter. One of those lines coincides with the system
's line of nodes, the line where the system's orbital plane crosses the plane of the sky. As a matter of definition, astronomers refer to the node where the system's secondary crosses the plane of the sky moving at least partly away from Earth as the ascending node.Inclination; the angle between the plane of the stars
' orbits and the plane of the sky. Imagine laying the orbit flat on our line of sight to the target star system. In that orientation the stars would appear to us to move from side to side on a straight line. We define that inclination as 90˚ and we measure the actual inclination of the system by an angle between 0˚ and 180˚. If the system has an inclination less than 90˚, the stars appear to revolve counterclockwise about our line of sight (which we imagine always passing through the system's barycenter) and we call the orbit prograde. If the system has an inclination greater than 90˚, the stars appear to revolve clockwise about our line of sight and we call the orbit retrograde.i=150.38
± 0.35 degrees.Position angle of the secondary
's ascending node; the angle between the Ecliptic north vector and the line of nodes, measured counterclockwise from the line pointing Ecliptic north toward the system's ascending node.Ω=32.88± 0.18 degrees.
Longitude of Periastron (or Argument of Periastron); the angle between the line of nodes and the orbit
's major axis (line of apsides), measured from 0˚ to 360˚ in the prograde direction (the direction of the secondary's motion) in the plane of the true orbit, from the secondary's ascending node to the secondary's periastronω=252.62± 0.16 degrees.
On a piece of stiff paper draw an ellipse of eccentricity equal to that of the orbit and draw an arrow indicating the direction of the star
's motion on the orbit that the ellipse represents. Imagine standing on the Ecliptic plane with the Ecliptic north pole directly overhead. Look toward the target star and so hold the paper that the line of apsides coincides with your line of sight and the north vector of the orbit (defined by the right-hand rule: when your right thumb, extended in a thumbs-up gesture, points north, the fingers of that hand curl in the same way that the body moves on its orbit) points Ecliptic north. Designate the farther focus of the ellipse as the barycenter, the system's center of mass. In that orientation your ellipse has a position angle of +270 degrees, an inclination of 90 degrees, and a longitude of periastron of 90 degrees. Rotate the paper counterclockwise about the line of apsides by -57.12 degrees (clockwise if you get a negative number). Turn the paper -17.38 degrees in the prograde direction about the orbit's north vector (retrograde if you get a negative number). And then tilt the paper +60.38 degrees about the line of nodes, turning the paper by the right-hand rule if you get a positive number and by the left-hand rule if you get a negative number, the appropriate rule stating that when the thumb of the appropriate hand points from the orbit's ascending node to its descending node, the fingers curl in the direction you must turn the paper. With the paper in that position you have a picture of the orbit of the system's secondary star. The ellipse represents the orbit of the system's primary star if you change the position of the barycenter from one focus of the ellipse to the other.Orbital Period: 168.93
" 0.43 Earth years.Time of Periastron passage: calculated out to AD 2300 from Twentieth Century. The presentation format is:
1. 1836.45
" 0.19 (AD 1836 Jun 14)2. 2005.38 (AD 2005 May 20)
3. 2174.31 (AD 2174 Apr 24)
4. 2343.24 (AD 2343 Mar 30)
The Stars Themselves
Star A:
Diameter; 1.3379 Sol (1,862,260 km).
Harvard Class; F0-V (7200±
500 degrees Kelvin).Mass; 1.3225 Sol.
Brightness; 4.325 Sol.
Habitable zone: 1.976 AU - 2.849 AU (2.08 AU, 2.609 years)
Star B:
Diameter; 1.3257 Sol (1,845,220 km).
Harvard Class; F0-V (7200
± 500 degrees Kelvin).Mass; 1.3165 Sol
Brightness; 4.2462 Sol.
Habitable zone: 1.957 AU - 2.822 AU (2.06 AU, 2.578 years)
Planetary system properties:
Stable planetary orbits lie within 1/5 of closest approach of components, 1.032 AU in this case. This system has no habitable planets, either revolving about one or the other of the stars or revolving about both stars.
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