Definition of Parallax

( Or, how mathematics enters into space )

"Education is what remains after one has forgotten everything he learned in school" - Albert Einstein ( 1879 - 1955 )

§ Definition of Parallax:

This is the difference in appearance of the position of an object as visually viewed from two separate locations. The best example of this phenomenon is when you hold forth your thumb at arm's length and then view your thumb first with one eye closed, then with your either eye closed. The simple result in this experiment will be an apparent movement or displacement in the position of your thumb. In fact, the closer your thumb to your face when you switch eyes, the more will appear the apparent displacement or movement of your thumb ( or object! ). Thus the amount of apparent displacement varies directly with distance to the object or thumb.

Well, so what?

Now inbetween these couple of lines of apparent sight of your "displaced" thumb is some angle which can give a true ( thumb, planet, star? ) position and therefore can be measured:

§ Parallax distance formula for the angular diameter apparent size:

This is the measured "visual diameter" as an angle in arcseconds as observed from a great ( astronomical ) distance.

§ Solar ( diurnal, geo - centric, horizontal ) Parallax:

This is the maximum geo - centric parallax calculated when the sun is simultaneously observed both at Earth's horizon and theoretically seen by another observer situated at Earth's center.

Therefore the solar parallax is the apparent maximum difference or displacement in the sun's observed position as seen simultaneously from the earth's center by one observer as opposed to another observer located one (1) earth ( semi - diameter ) radius away using earth's diameter as a baseline and considering that the mean average distance between earth and the sun is, by definition, one astronomical unit or 1.0 AU.

The solar parallax is also often stated as the angular size of earth's equatorial radius or the angle subtended by earth's mean equatorial radius drawn from the sun's center at 1.0 AU ( astronomical unit ) distance between earth and sun.

The authorized and accepted solar parallax is calculated at 8.794143" or ≈ 8.80" ( arcseconds ). Source: The Astronomical Almanac is a joint publication of the U.S. Nautical Almanac Office, United States Naval Observatory (USNO), in the United States and Her Majesty's Nautical Almanac Office ( HMNAO ), United Kingdom Hydrographic Office ( UKHO ), in the United Kingdom. See: http://asa.usno.navy.mil/.

§ Venus Parallax:

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