Astronomy. lecture sept 17/ 13
The milky way galaxy has a big black hole in centre were about 26000 thousand lights
year away from earth.
TheAndromeda galaxy is 2.5 milly yr away. its the nearest large galaxy to the milky way.
in general near by galaxies are million years away
• there are many solar systems in each galaxy there are many galaxies in the universe, there
are many solar systems in the universe.
• when we look at the sun we see it as it is now.
-Light travels at a finite speed
• so, no matter where you look, you are looking back in time
• light takes time to travel anywhere you look you are looking back in time. in astronomy
that is a significant factor we have to take in account
if you stand 1 meter away from light bulb if i turn it on takes it a tiny perceptible amount
of time to hit your eyes 3 billions of a second.
you never see sun as it is now you can only see sun the way it is 8 minutes ago if your on
earth. 1 au FROM Sun
if you want to control a robot near sun that means its really hard to say steer on earth that
signal propagates towards sun 8 minutes later probe moves to right.
• delay gets huge when you consider further objects, andrameda galaxy 2.5 million light
see light fmor there 2.5 million yrs later.
stars produce light fmor life time even though dead light still coming to us.
Billions of light years
light you see left distant galaxies billions of years ago.
• 70 million years ago, a very clever dinosaur fired his laser pointer at a
mirror 35 million light years away. when would eh see the reflected
E. The dinosaur would never see the reflected pulse we would see it.
would take light 70 million years.
• STARS are balls of plasma which produce energy by nuclear fusion
the sun is not on fire its producing energy bu fusion talk about that
later stars are distinguish from planets
PLANETS are rocky, icy or gassy, and they don't produce much energy.
Planets orbit stars, there are tons of planets, definition can get murkier.
they can be liquify,
lpanets do not produce significant quantities of energy.
In 2006, the international Astronomical union (IAU)
accepted a new definition of the term "planet"