Parallax and the Standard Candle Method How Far To That Star? Parallax and the Standard Candle Method

Two Ways to find How Far The Parallax Method uses the change in the direction to the star as the Earth orbits to find the distance to a relatively nearby star. (less than 250 parsecs, or 815 LY) It uses Triangulation to find the distance. The Standard Candle Method compares Apparent magnitude to Absolute Magnitude to find the distance to more distant stars and even other galaxies It uses the Inverse Square Law.

A Third Method-Red Shift Another way to find the distance is to measure the amount of red-shift in the star’s or galaxy’s light. It is based on the assumption that due to the Big Bang the farther away an object is the greater its red-shift must be. It is only usable for extremely distant objects (millions of LY away!). Astronomers use this method as a last resort due to it being based on an assumption.

Using Parallax To use parallax you first have to find the measure of the angle To do this you Measure in degrees (p) the difference in direction to the star compared to a reference object at the maximum displacement ( Should be 6 months apart)

(see diagram & formula on board) Next calculate the distance using basic trigonometric function: Tangent. The distance to the star will be the half the baseline, “b” (in this case b = 1 AU or 150,000,000 km, the average distance from the Earth to the Sun). Divided by the tangent “p,” half the parallax angle P (see diagram & formula on board)

Parallax and the Parsec To make using parallax easier Astronomers invented the measure of distance called a parsec. A parsec is defined as the distance at which a star will have a parallax of one second of an arc as seen from Earth. That is a “parallax-arc second” or “parsec.” The distance that this is true is about 3.26 Light-Years, thus 1 parsec = 3.26 LY If the parallax angle is given in arc-seconds it is… (Formulae on Board)