The Astrogators’ Guide to

18 Scorpii

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    This star is an almost identical twin of our sun. That fact alone justifies a visit if the star has any planets (none have been discovered as of 2014).

Location in Space

Radial Distance:

    Parallax = 0.07194±0.00037 arc-sec, which leads to;

        1. 45.3 ± 0.2 lightyears (13.90 ± 0.07 parsecs).

        2. 2,867,083 ± 14,440 AU.

Equatorial Coordinates:

    Right Ascension; 16 hr, 15 min, 37.26946 sec +1.538t sec.

    Declination; -8 deg, 22 min, 09.9870 sec - 49.553t arc-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 244 degrees and then south (down) by 8-1/3 degrees.

Ecliptic Coordinates:

    Ecliptic Latitude; +12.702 deg - 44.732t arc-sec.

    Ecliptic Longitude; 296.493 deg + 31.418 arc-sec.

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

    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 296-1/2 degrees, and then shift your gaze northward by 7-3/4 degrees along a line perpendicular to the Ecliptic.

Galactic Coordinates:

    Galactic Latitude; +29.157 deg - 35.910t arc-sec.

    Galactic Longitude; 4.696 deg + 41.213t arc-sec.

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

    Look toward the radio source Sagittarius-A by casting your gaze across the Orion-Sagittarius Gap toward the Sagittarius-Carina Arm of the galaxy and at a point about six degrees south of the Ecliptic on the west (right) side of Sagittarius and two degrees south of X Sagitarii (the point of the arrow in the Archer’s bow). Then move your gaze in an easterly direction along the plane of the Milky Way by 4-2/3 degrees. Then tilt your gaze by 29 degrees in a northerly direction, more or less upward and to your right, at right angles to the plane of the Milky Way.

Annual Proper Motion

    in Right Ascension = +0.23077 arc-sec/yr = 15.194 km/sec = 3.205 AU/yr.

    in Declination = -0.49553 arc-sec/yr = 32.626 km/sec = 6.882 AU/yr.

        Total Proper Motion = 0.54663 arc-sec/yr = 35.990 km/sec = 7.592 AU/yr in a direction 155.03˚ counterclockwise from due celestial north, 144.92˚ counterclockwise from due Ecliptic north, and 131.07˚ counterclockwise from due Galactic north.

    in Radial Distance = +11.6 km/sec = 2.447 AU/yr.

        Total motion = 7.9766 AU/yr = 37.8129 km/sec.

    From the present; 110,158 years ago 18 Scorpii reached its perihelion 43.116 lightyears (2,726,324 AU) from Sol in the southwestern corner of the constellation of Ophiuchus and then crossed 17.86 degrees of sky to reach its present position.

Orientation in Space

We generally only get this information for binary stars.

The Star Itself

        Diameter; 1,405,819 ± 12,527 km (1.010 ± 0.009 Sol).

        Harvard Class; G2Va (5,433 ± 69 Kelvins).

        Age; 4.1 - 5.3 billion years.

        Mass; 1.02 ± 0.03 Sol.

        Brightness; 1.058 ± 0.028 Sol.

        Habitable zone: 1.12 ± 0.06 AU; 430 ± 40 days.

        Surface composition: hydrogen 73.56%, helium 24.45%, other 1.99% (Sol = hydrogen 73.7%, helium 24.5%, other 1.81%)


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