01ch1Tour2

# 01ch1Tour2 - Chapter 1 Topics A short survey of the whole...

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Chapter 1: Topics A short survey of the whole course main parts of the universe Light-year Sky changes with Seasons Constellations (more in later classes) Scientific Method data - hypothesis – theory Astronomical measurement units Scientific notation, units, prefixes The aims of the chapter are given in small box upper right, p1. of book.

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Powers of Ten Each image is 100 = 10 2 times larger than the one before. 9 steps increase the size by a factor of (10 2 ) 9 = 10 18 expanding the Earth to the part of the universe we can see. See p.12 of ed. 3 the book.
Astronomical Distances We use cm, m and km for small distances. We use light-years for distances (its not a time) to stars and galaxies. 1 Ly = distance light travels in 1 year. distance = speed x time, d=st, or d=vt with v=velocity 1 Ly = speed of light (m/s) x time (s/year) speed of light = c = 2.9979 x 10 8 m/s = 186,000 miles per second. 1Ly = 9.53 x 10 12 km = 60,000 x Earth-sun distance Question: How far. . How long would it take. .

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Meteors Meteors Grains of sand ablating 60 miles up in the Earth’s thin outer atmosphere. You can see about 6 meteors per hour when its dark, each for 1 second.
The moon – a natural satellite

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The sun - a typical star
Five Bright Planets: Five Bright Planets: Mercury, Venus, Mars, Jupiter and Saturn – visible by eye They are not visible when too near to the sun in the sky, or below your horizon. See from zero to 5, depending on the year, month and time of night. Mercury Venus Mars Saturn Jupiter is off picture

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You can not see all 8 planets because… You can not see all 8 planets because… Uranus needs binoculars and Neptune a telescope. Pluto is a large comet. These 3 are too distant, and hence too faint for the naked eye. In day time the sky is too bright to see any planets. Any planet could be too near the sun in the sky , and hence not visible for months at a time. Like the sun, moon and stars, each planet spends part of each 24 hour day below your horizon and part above.
Planets look like the brightest stars Planets look like the brightest stars

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Planets Move Relative to the Stars Planets Move Relative to the Stars Hyades open star cluster Jupiter Saturn Pleiades open star cluster
Planets show Discs in Telescopes Planets show Discs in Telescopes Jupiter Saturn

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Most stars look like points in Telescopes Most stars look like points in Telescopes Spikes and rings are not real - caused by telescope. The haze is real – hot gas.
Our Solar System: all that orbits our sun The Earth is one of 8 planets (Pluto is a comet) in our solar system . There are also satellites, minor bodies (comets, asteroids, meteoroids), gas and dust.

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Comets Most comets live in the outer edges of the solar system, far beyond the planets but nearer than the next stars. Every few years a comet
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01ch1Tour2 - Chapter 1 Topics A short survey of the whole...

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