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ay45c2-page13 - iii parallax(using Earth's orbit p 1 AU to...

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Unformatted text preview: iii) parallax: (using Earth's orbit) p 1 AU to distant objects (providing reference frame) p p p Angles p are small (< 100) and the distance D = R=p. If R = 1 AU, and p is measured in seconds of arc, then D comes out in parsecs. 1 pc = distance at which 1 AU subtends 1 arcsec = 3:086  10 cm. 18 iv) inverse square law and \standard candles" If you know that a certain object has luminosity L (e.g., by looking at similar objects near you) [L in erg/sec or watts], then the distance of that object is given from its observed ux L F = 4D : 2 (Remember F is in energy/sec/unit area.) Sphere D Source 22 ...
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