right, we have 2 threads discussing planets now...

sun appears to move backwards in the sky from night to night--changing which background constellation it is near from month to month--the zodiac

Brahe had very precise measuring instruments and discovered commits and witnessed a supernova. He detected no parallax motion and so concluded that the sun goes around the earth because if the earth were moving he'd've seen parallax motion

*parallax motion is closer stars seeming to move in relation to background/more distant stars as earth moves and changes view of them

I wonder how much of this history stuff is actually going to be on the exam...

Brahe's assistant Kepler used the data he helped Brahe get and discovered that planets moved in a elliptical motion rather than a spherical one and that the sun is at one of the ellipses

the orbital speed of a planet depends on how close or far away from the sun the planet is (like a ball being swung on an ellipse at the end of a rubber band--will slow down as gravity pulls it back, spring back and around, repeat)

therefore Kepler didn't agree with Brahe or most others but rather thought that the sun was what was at the center of the universe not earth

he had data instead of logic on his side--more scientific now

Learning more here, in the holidays, than at school XD

P³=a²

 

P = the amount of time it takes for the planet to make one orbit

 

a: the length of the orbit's semi major axis

Edited December 15, 201114 yr by Aiel Heart

Cool!

mornings!

is this astrophysics?

if so then it is awesome

Galileo made many discoveries:

 

the sun has sunspots and thus isn't perfect

 

there are mountains on the moon

 

he discovered that there were 4 objects (that he could see) that orbited Jupiter--there were things that didn't orbit the earth OR the sun!!!

 

and he also discovered that Venus has phases just like the moon does--which means that both venus and earth must be orbiting the sun!!!!

Edited December 15, 201114 yr by Aiel Heart

hello :D

we're learning about Astronomy today

he was able to discover all of this with a very good telescope he made--he is called the father of modern astronomy

we now know what happens.... but we still don't know why

 

there is also the lack of parallax motion that must be explained

this guy named Newton did a lot of studying and came up with three laws of motion

1) A body at rest will remain at rest or a body in motion will remain in motion unless acted on by a force

A body resists change of motion

Important note: the first law ‘cares’ whether the change is in AMOUNT or in DIRECTION or both!

2) For a given force applied, we get a given acceleration

BUT, the AMOUNT of acceleration depends on the AMOUNT of matter present

 

F = m x a OR a = F / m

 

F= force

a=acceleration

m=mass

 

Example: The same force is applied to two objects, the more massive object is accelerated less than the less massive object

 

Force is measured in Newtons

3) Any two bodies with mass attract each other with the same force

 

but wait.... that means that the earth and the sun are pulling on each other the same... right?

WRONG