The Astrogators’ Guide to

Altair

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    Also know as Alpha Aquilae.

Location in Space

Radial Distance:

    Parallax = 0.19495±0.00057 arc-sec, which leads to;

        1. 16.73 ± 0.05 lightyears (5.13±0.01 parsecs).

        2. 1,058,140 ± 2,063 AU.

Equatorial Coordinates:

    Right Ascension; 19 hr, 50 min, 46.99855 sec + 3.575t sec.

    Declination; +8 deg, 52 min, 5.9563 sec + 38.529t 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 297-2/3 degrees and then north (up) by almost 9 degrees.

Ecliptic Coordinates:

    Ecliptic Latitude; +29.3038 deg +26.2847t arc-sec.

    Ecliptic Longitude; 238.2257 deg + 60.5725t 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 238-1/4 degrees, and then shift your gaze northward by 29-1/3 degrees along a line perpendicular to the Ecliptic.

Galactic Coordinates:

    Galactic Latitude; -8.909 deg + 58.406t arc-sec.

    Galactic Longitude; 47.744 deg + 30.8t 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 47-3/4 degrees. Then tilt your gaze by almost 9 degrees in a southerly direction, more or less downward and to your left, at right angles to the plane of the Milky Way.

Annual Proper Motion

    in Right Ascension = 0.53623 arc-sec/yr = 2.75 AU/yr = 13.039 km/sec.

    in Declination = 0.38529 arc-sec/yr = 1.976 AU/yr = 9.369 km/sec.

        Total Proper Motion = 0.6603 arc-sec/yr = 3.387 AU/yr = 16.056 km/sec in a direction 54.302˚ counterclockwise from due celestial north, 66.54˚ counterclockwise from due Ecliptic north, and 27.80˚ counterclockwise from due Galactic north.

    in Radial Distance = -26.1±0.9 km/sec = 5.506±0.19 AU/yr.

        Total motion = 6.464 AU/yr = 30.644 km/sec.

    From the present; in 139,404 years Altair will reach its perihelion 8.766 lightyears (554,298 AU) from Sol in the middle part of the constellation of Lacerta after crossing 58.4 degrees of sky.

Orientation in Space

We generally only get this information for binary stars.

The Star Itself

        Diameter; 2,268,797 – 2,825,557 km (pole to equator); 1.63 – 2.03 Sol.

        Harvard Class; A7V (6,900 - 8,500 Kelvins).

        Age; over one billion years.

        Mass; 1.79 Sol.

        Brightness; 10.6 Sol.

        Habitable zone: 3.55±0.18 AU; 4.8±0.5 years.

        Surface composition: not found. The star is a Delta Scuti variable.

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