# Ast lec 1.docx

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23 Apr 2012
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Ast lec 1
- (AST2S1; astrobiology)
- Relative distance;
o Where are we- when listing our address it starts with a number <__ is the smallest,
same in location
Our address= earth, solar system, milky way galaxy (member of group of30-31
largest is the andromia galaxy, ours is relatively small), local group, local super
cluster, universe
o Relative sizes; terestial planets are mercury, mars, venus, earth all made of rock (earth is
the biggest). Uranus, Neptune, Saturn, Jupiter, 10 earths across to make the diameter of
Jupiter, is so big is it could turn into a star. 10 earths across the sun but our sun is a low
mass star
o Relative sizes of galaxies; 200 billion stars in a galaxy, in virgo A the biggest, there are a
few this big
o Relative distances (now on slides); next nearest star is in ajax from lecture hall, what can
you conclude about the distances btwns tars and distances btw galaxies?- galaxies are
relavtively close to each other, the chances of two galaxies colliding is probable, stars
are far from each other depending on the size
- Common distance units used in astro;
o The astronomical unit (AU); ppl often say jupitar is 5 AU, means the distance btwn
jupitar and sun is 5 times the distance of the earth and sun, (earth orbit is not perfectly
circle but are talking about average) so average distance btwn eath and sun. Is only ok
to use inside the solar system and therefore not useful for outside it so now we use a
light year
o Lightyear (ly): distance that lights travel in one year (vauge distance) everything is
measured within the milky way galaxy is measured in ly. Nearest star to the sun is 4 ly
away (eg.) once outside of the milky way galaxy, larger units are parsec (is the biggest
unit used, but nbot be enough megaparsec- 1 million parsec)
- Our motion in space;
o Rotates on its axis every 24 hrs (the earth), you have the same velocity of earth so can
feel it
- Concept test: put objects from nearest to furthest from earth: moon, mars, sun, Jupiter,
Neptune, stars
- Concept test: correct order nearest to farthest from earth: the sun, Neptune, nearest star, milky
way centre, Andromeda galaxy
- Concept test: how long would it take to reach nearest star alpha centauri; 4 lightyears
- Modern scientific method;
o newtons law only worked with low speed so need high speed to explain why the orbit
of mercury was the way it was which became the einstiens law of relativity. Is not wrong
but has a limit, it can change
o Scientific laws are not absolute truth, they can be changed over time if a law is shown
not to work under a certain scale and so scientists need to be able toreject
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