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Transcript
Objectives How Big are things in Space? measurement in space • To identify the units we use to measure different objects in space • Define what an astronomical unit is • Define what a light year is • To describe parallax and identify how to use parallax to measure distance in space • To identify when to use the inverse square law to determine the distance to a star – Explain what the inverse square law says The Astronomical Unit • The distance between the earth and sun is: – 150,000,000 km or – 93,000,000 miles • To avoid using such large numbers, we use the Astronomical Unit, or AU. • 1 AU = average distance between the Earth and the Sun. • 1 AU ~ 150 million km ~ 93 million miles. • We can use AU to measure things in our solar system. Some approximate, average orbital radii sizes: Mercury: 0.4 AU Mars: 1.5 AU Saturn: 10 AU Pluto: 40 AU Parallax • Objects that are closer to us will seem to move faster and have LARGER parallax angles Parallax • Now that we have easy units to use when we measure objects in space, now we need a way to measure moving objects in space • We can use a little bit of algebra and a concept called parallax. – We use telescopes to chart a stars position in relation to other stars in the sky – Six months later, we do the same thing. The star seems to move because of parallax. Parallax Examples – moon, planets, comets • Objects that are farther away from us will seem to move slowly or not at all and have the smallest parallax angles – EVERYTHING ELSE Parallax Animation Parallax Animation 1 Parallax Animation Inverse Square Law • Parallax works for objects that are fairly close to us, but not for stars that are very far away from us. Why? – There is no detectable change in the position of the star over the 6 month period • We can use the Inverse Square Law to help us. The farther you are away from an object, the dimmer it appears to be, because less light will reach you Inverse Square Law Inverse Square Law Animation 2