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AST251H1 Lecture : Lecture 2, Physics and the Universe Gravity, heliocentric system, atomic spectra, composition of the universe

Newton: theory of gravity explains all planetary motions. Electromagnetic radiation allows us to characterize each element and molecule. Find out what the sun is made of. Speed of light c=300 000 km/s, highest possible velocity. Oort cloud, kuiper belt are found beyond the nine planets. Neptune, the last (8th) planet: 4 light hours. The oort comet cloud: extends to about a light week. The nearest star: 4 light years and 1 au as the distance from sun to earth. 1 parsec is the distance corresponding to a parallax angle of 1 arc-second. Sun is 0. 01 au in diameter; neptune"s orbit is 30 au. The nearest stars are &gt;1 parsec or 4 ly away. Visible light images of the milky way show black blotches. 1000 ly thick by 100 000 ly diameter. Sun is in the disk, 28 000 ly out from the centre. At least 100 billion stars in this galaxy.

Canada

Life on Other Worlds

Astronomy & Astrophysics

Harald Pfeiffer

University of Toronto St. George

Why do astronomers find it difficult to locate extrasolar planets with telescopes?
A. From our distance, they are very close to the stars they orbit.
B. Planets wobble due to the gravity of the stars they orbit.
C. Planets only emit invisible wavelengths of light.

The speed of light in a vacuum is exactly 299,792,458 m/s. This speed is sometimes used to provide a convenient yardstick for large astronomical distances. (a) A light-second is the distance light travels in one second. If the Moon is 3.84×108 m from the Earth (center to center), how many light-seconds away is it? (b) A light-minute is the distance light travels in one minute. If the Earth is 1.50×1011 m from the Sun, how many light-minutes away is it? (Your answer also represents the number of minutes it takes for light to reach the Earth from the Sun.) (c) A light-year is the distance light travels in one year. The Sun is 28,000 light-years from the center of the Milky Way galaxy. What is this distance in meters?

it is estimated that the nearest star outside the solar system is 4.0×10^16m away. express this distance in light year, where one light year is the distance that light travels in one year. (take the speed of light to be 3.0×10^8 m s-1

AST251H1 Lecture : Lecture 2, Physics and the Universe Gravity, heliocentric system, atomic spectra, composition of the universe

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