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    Altitude Corrections

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    Insan Ahammad
    The document discusses altitude corrections when taking sextant measurements of celestial objects. It explains that the observed altitude is calculated by adjusting the sextant altitude for index error and dip. The apparent altitude is then calculated by subtracting dip from the observed altitude. Finally, the true altitude is determined by applying total corrections to the apparent altitude. It provides three examples calculating true zenith distance by working through these correction steps.

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    Altitude Corrections

    Uploaded by

    Insan Ahammad
    148 views14 pages
    The document discusses altitude corrections when taking sextant measurements of celestial objects. It explains that the observed altitude is calculated by adjusting the sextant altitude for index error and dip. The apparent altitude is then calculated by subtracting dip from the observed altitude. Finally, the true altitude is determined by applying total corrections to the apparent altitude. It provides three examples calculating true zenith distance by working through these correction steps.

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    How to make Altitude Corrections in easiest way.

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    The document discusses altitude corrections when taking sextant measurements of celestial objects. It explains that the observed altitude is calculated by adjusting the sextant altitude for index error and dip. The apparent altitude is then calculated by subtracting dip from the observed altitude. Finally, the true altitude is determined by applying total corrections to the apparent altitude. It provides three examples calculating true zenith distance by working through these correction steps.

    Copyright:

    © All Rights Reserved
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    148 views14 pages

    Altitude Corrections

    Uploaded by

    Insan Ahammad
    The document discusses altitude corrections when taking sextant measurements of celestial objects. It explains that the observed altitude is calculated by adjusting the sextant altitude for index error and dip. The apparent altitude is then calculated by subtracting dip from the observed altitude. Finally, the true altitude is determined by applying total corrections to the apparent altitude. It provides three examples calculating true zenith distance by working through these correction steps.

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    © All Rights Reserved
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    ALTITUDE CORRECTION

     Visible Horizon – (VV1) - Small circle


    on the surface of the earth
    representing the observer's field of
    vision.
     Sensible horizon – Small circle on the
    celestial sphere whose plane is parallel
    to the rational horizon, and which
    passes through the observer’s eye.
    Corrections
     Index Error
    – ‘on the arc’ is subtracted from the sextant
    altitude to get observed altitude.
    – ‘off the arc’ is added to the sextant altitude to
    get observed altitude.

    Sextant Altitude (SA) +/- Index Error


    (IE) =Observed Altitude (OA)
     Dip (Height of Eye)
    – Dip is the angle between the visible Horizon and
    the sensible horizon. It is always negative.

    Observed Altitude – Dip = Apparent


    Altitude.
     Total Corrections
    – Allows for refraction, parallax and semi-diameter
    (where applicable).
    – SUN: Entered with Date, Limb, and A.A.
    – Planets: Entered with A.A. Note: additional
    corrections for Venus & Mars.
    – Stars: Entered with A.A.

    Apparent Altitude (AA) +/- Total Corrections


    (TC) = True Altitude (TA)
     True Zenith Distance

    90 degrees minus TA = TZD


    Example 1

     The Sextant Altitude of the Sun’s lower


    limb on 29th June 1995 was 37° 15.8’.
    Index error 0.7’ On the Arc, Height of
    Eye 7.2m. Calculate the True Zenith
    Distance.
     Sun (LL) = 37° 15.8’ 29th June 1995. IE= 0.7 on.
    HE=7.2m
     S. A. 37° 15.8’
     I.E ____-0.7
     O.A. 37° 15.1’
     Dip ____-4.7
     A.A. 37° 10.4’
     T.C. __+14.7
     T.A. 37° 25.1’
     90 90° 00.0
     TZD 52° 34.9’
    Example 2

     The Sextant Altitude of Mars on 5th


    March 1995 was 22° 13.7’. Index error
    1.3’ Off the Arc, Height of Eye 4.6m.
    Calculate the True Zenith Distance.
     Mars SA = 22° 13.7’. 5th March 1995. IE=1.3’ off. HE=4.6m
     S. A. 22° 13.7’
     I.E ___+1.3
     O.A. 22° 15.0’
     Dip ____-3.8
     A.A. 22° 11.2’
     T.C. -2.4
     Additional Corr’n _ +0.2
     T.A. 22° 09.0’
     90 90° 00.0
     TZD 67° 51.0’
    Example 3

     An observer obtained a Sextant


    reading of Sirius during morning
    twilight on 5th March 1995 was 22°
    13.7’. Index error of the sextant was
    1.1’ Off the Arc, Height of Eye 43.3m.
    Calculate the True Zenith Distance.
     Sirius = 52° 28.5’ morning twilight. 29th June 1995. IE= 1.1
    off. HE=43.3m.
     S. A. 52° 28.5’
     I.E ___+1.1
     O.A. 52° 29.6’
     Dip ___-11.6
     A.A. 52° 18.0’
     T.C. ____-0.8*
     T.A. 52° 17.2’
     90 90° 00.0
     TZD 37° 42.8’

     * Note 52° 18’ is a critical number and the correction must be


    taken from the upper figure.

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