The Astrogators' Guide to


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    Pronounce Pro-kyon. Also known as Alpha Canis Minoris, Algomeysa (Elgomaisa) or Antecanis. This is the next star that an expedition would explore after Sirius (Alpha Canis Majoris), which lies 5.2 lightyears away.

Location in Space

Radial Distance:

    Parallax = 0.28593 0.00088 arc-seconds, which leads to;

       1. 11.407 lightyears 0.035 lightyear (3.4969 0.01073 parsecs).

       2.  721,383 AU 2,220 AU.

Equatorial Coordinates:

    Right Ascension; 7 hr, 39 min, 18.113 sec - 4.74t sec.

    Declination; +5 deg, 13 min, 29.95 sec - 102.4t arc-sec.

        [t measured in centuries, Jan 2000 is t = 0]

Imagine standing on the north side of Earth's equatorial plane with the north celestial pole directly overhead and look toward the First Point of Aries (the point where the Ecliptic crosses the celestial equator, which now lies in Pisces, slightly southwest of the Circlet). Slide your gaze eastward (to your left) about one-eighth of a degree less than 115 degrees along the celestial equator, reaching a point south of where the Ecliptic passes through Gemini. Then tilt your view north a little less that 5-1/4 degrees. Procyon is the brightest star in your view at that point.

Ecliptic Coordinates:

    Ecliptic Latitude; -15.9703762 deg - 88.972t arc-sec.

    Ecliptic Longitude; 115.7764721 deg - 87.38t arc-sec.

        [t measured in centuries, Jan 2000 is t = 0]

Imagine standing on the north side of the Ecliptic plane with the Ecliptic north pole directly overhead and look toward the First Point of Aries. Slide your gaze eastward along the Ecliptic (the line that the sun traces through the Zodiac in the course of a year) a little over 115-3/4 degrees, reaching a point in the constellation of Gemini. Then tilt your view south a little less than 16 degrees. Procyon is the brightest star in your field of view.

Galactic Coordinates:

    Galactic Latitude; +13.03 deg - 59.06t arc-sec.

    Galactic Longitude; 213.69 deg - 109.83t arc-sec.

        [t measured in centuries, Jan 2000 is t = 0]

Look across the Orion-Sagittarius Gap toward the Sagittarius-Carina Arm and at a point about six degrees south of the Ecliptic on the west (right) side of Sagittarius and two degrees south of X Sagittarii (the point of the arrow in the Archer's bow). Move your point of view a little less than 213-3/4 degrees left along the plane of the Milky Way and then slightly more than 13 degrees north, more or less upward and to your left, at right angles to the plane of the Milky Way. You will then be looking almost directly at Procyon.

Annual Proper Motion

    in Right Ascension = -0.706 arc-sec/yr (2.469 AU/yr = 11.705 km/sec).

    in Declination = -1.028 second per year (3.595 AU/yr = 17.044 km/sec).

        Total Proper Motion = 1.247 arc-sec/yr (4.361 AU/yr = 20.674 km/sec) in a direction 214.5 degrees counterclockwise from due celestial north, 224.48 degrees counterclockwise from due Ecliptic north, and 241.73 degrees counterclockwise from due galactic north.

    in Radial Distance = -4.1 km/sec = 0.8649 AU/yr.

        Total motion = 4.446 AU/year = 21.078 km/sec.


From the present; in 323,140 years Procyon will become an eclipsing binary for about 189 years as its orbital plane passes over the Sol-Procyon line and in 31,490 years Procyon will reach its perihelion 11.19 lightyears (707,574 AU) from Sol in the southwest central part of Canis Minor after crossing 11.19 degrees of sky.

Orientation in Space

    Orbit size: 15.18 AU = the semi-major axis of the combined orbits of the two stars in mutual revolution about their common barycenter. The ellipse of the orbit has eccentricity, e=0.407. The minimum and maximum separations between the two stars = 9.00 -- 21.36 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 Procyon system 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 (the white dwarf Procyon B in this case) 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. Because their orbit has an inclination less than 90 degrees, the stars of Procyon appear to us to revolve counterclockwise about their barycenter.

i=31.1 0.6 degrees.

    Position angle of the secondary's ascending node; the angle between the Ecliptic north vector (projected onto the sky) and the line of nodes, measured counterclockwise toward the system's ascending node.

Ω=97.3 0.3 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 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 periastron

ω= 92.2 0.3 degrees.

    On a piece of stiff paper draw an ellipse of eccentricity e=0.407 and draw an arrow indicating the direction of the star's motion on the orbit that the ellipse represents. Look toward Procyon 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. Turn the paper counterclockwise 7.3 degrees, then so turn it that the orbit turns in the retrograde direction by 177.8 degrees, and finally turn it 58.9 degrees about the line of nodes in accordance with the left-hand rule (with your left thumb pointing from the ascending node to the descending node, your fingers curl in the direction you must turn the paper).

    Orbital Period: 40.82 0.06 years.

        Time of Periastron passage:

            1. 1927.15 (AD 1927 Feb 24)

            2. 1967.97 0.05 (AD 1967 Dec 20)

            3. 2008.79 (AD 2008 Oct 16)

            4. 2049.61 (AD 2049 Aug 11)

            5. 2090.43 (AD 2090 Jun 06)

            6. 2131.25 (AD 2131 Apr 01)

            7. 2172.07 (AD 2172 Jan 26)

            8. 2212.89 (AD 2212 Nov 21)

            9. 2253.71 (AD 2253 Sep 16)

            10. 2294.53 (AD 2294 Jul 13)

The Stars Themselves

    Procyon A:

        Diameter; 2,588,900 km (1.86 Sol)

        Harvard Class; F5 IV (6650 K)

        Age; 1.7" 0.3 billion years

        Mass; 1.497" 0.037 Sol

        Brightness; 7.73 Sol

        Habitable zone: 2.78 AU, 3.79 years

        Surface composition: hydrogen 71.5%, helium 25.8%, other 2.74% (Sol = hydrogen 73.7%, helium 24.5%, other 1.81%)

    Procyon B:

        Diameter; 17,000 km ( 0.02 Sol)

        Harvard Class; DA-F or A-F VII ( 8,700 K)

        Age; 1.7" 0.3 billion years

        Mass; 0.602" 0.015 Sol

        Brightness; 0.00055 Sol

        Habitable zone: 0.024 AU, 1.75 day

        Surface composition: hydrogen 69.4%, helium 27.7%, other 2.89%

Planetary system properties:

    Stable planetary orbits lie within 1/5 of closest approach of components, 1.80 AU in this case, well outside the habitable zone.


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