PHYS 005 Lecture Notes - Lecture 4: Chemical Element, Parsec
4 Jul 2018
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Reading- Ch. 5 Sect. 1,2,6,8
Photons- particles of light
●photons bounce back- detection of light
●Astronomers study photons reflected by planets & moons
○lights= photons
Stars emit light
Planets & moon reflect
light
Galaxies emit
light & certain parts reflect
light
Light reaches your eyes as its final destination
½ degree = size of the moon
●Measure angular distance between 2 stars & size of planets
●1 parsec= 3.26 light years (DISTANCE, not speed)
○Mega (millions) parsecs, giga parsecs, kilo (thousands) parsecs
■Sun- 8 kiloparsec from Milky Way
■Andromeda is 8300 parsecs
Galileo (1600)
●Sound travels at .3 km/s in air
●Light- 297,792 km/s in air
○Light seen before the sound reached (too fast to measure)
○Counted by heartbeats-no measurement quick enough to measure light
If Jupiter 5x further from Sun than the earth
●5 light min. X 8 light min= 40 light minutes away from Sun
●***when earth is BEHIND sun
○16 light min. + 32 min= 48 min (6x8)- additional 8 light min.
●Jupiter- 67 moons
○4 bigger- Callisto, Ganymede, Io, Europa (inner to outer)
Galileo noticed that there were things going around Jupiter ( v. everything revolves around earth)
●Jupiter eclipsed moon when there wa a shadow on Jupiter
○Io, europa, ganymede, callisto
Romer (1676)
●Took io & calculate when io was about to enter behind jupiter (when we lost IO)
○32 min for light fr. jupiter to meet earth
○If we were behind the sun, it would take 16
more min. (2 8 light min)
●Got the speed of light 26% lower than it actually is (220,000 km/s)
Fizeau (1850)
●Rotating mirror where light goes through and reflects
●Speed of light ,06% lower than it actually is- IMPRESSIVE
○297,792.458 km/s- C
Document Summary
Astronomers study photons reflected by planets & moons. Galaxies emit light & certain parts reflect light. Light reaches your eyes as its final destination. Measure angular distance between 2 stars & size of planets. 1 parsec= 3. 26 light years (distance, not speed) Mega (millions) parsecs, giga parsecs, kilo (thousands) parsecs. Sound travels at . 3 km/s in air. Light seen before the sound reached (too fast to measure) Counted by heartbeats-no measurement quick enough to measure light. If jupiter 5x further from sun than the earth. X 8 light min= 40 light minutes away from sun. + 32 min= 48 min (6x8)- additional 8 light min. 4 bigger- callisto, ganymede, io, europa (inner to outer) Galileo noticed that there were things going around jupiter ( v. everything revolves around earth) Jupiter eclipsed moon when there wa a shadow on jupiter. Took io & calculate when io was about to enter behind jupiter (when we lost io)
