Orbit Theory 2
Planets (mass) will orbit another body when the force of gravity is equal to the force of acceleration (centripetal force) that exists between the 2 bodies.
Orbiting bodies follow an elliptical shaped orbit about the more massive body (in our case the Sun).
In the early era of astronomy it was thought that the orbits were circular, as that was regarded as being more "perfect".
Most planets orbit in an elliptical orbit where the ratio of major to minor axis is greater than but close to one (almost circular orbit). The greater the greater the eccentricity of an orbit the more elliptical it is.

m = minor axis
M= major axis
a = distance between a point
on the ellipse and the first focus
b = distance between the same
point and the second focus
a+b = constant


where m = eccentricity

INTERACTIVE ORBITER give this interactive tool a try and change the variables to observe the affects. Why are comets moving so fast when they approach the sun?

a )What happens to the characteristics of the orbit of a body when the eccentricity is increased?



b) What happens to the  velocity of a body with some eccentricity when it approaches the perihelion and the aphelion?


c) How can you account for the energy in the orbiting system that behaves this way (eccentric orbit) ?

 

 

 

 


Note that most of the planets in our solar system revolve in nearly perfect circles and in the same plane( ecliptic).
a)  Why is Pluto not in the same ecliptic as the rest of the planets??

 

b) Why does Mercury have the fastest period of revolution?

a) Why does the Sun appear to stay in one of the focal points while the planets move about the ecliptic?
Clik for a simulation: drawing an ellipse

 

 

 

 

 

 

 

 

 

a) Some comets arrive in from outer space and approach the Sun but continue back out to space rather than into orbit  explain why?


b) In a circular orbit what is greater the major or minor axis?


What causes the various elliptical orbits of planets and comets?

 

 

 

 

 

 


Escape velocity- this is the speed that an object of any mass needs to escape the force of gravity of that planet (body)
> Force acceleration exceeds the force of gravity.
> This is 11.2 km/s for the Earth (40,300 km hr-1. )
Geosynchronous orbit

> satellites in geosynchronous orbit circle the earth once each day over precisely the same place on earth

> usually this is for communication purposes such as .... phones,  GPS,etc

>  the time it takes for a satellite to orbit the earth is called its period
> for a satellite's orbit period to be one sidereal day, it must be approximately 35,786 kilometers (19,323 nautical miles or 22,241 statute miles) above the earth's surface ,  higher than the Shuttle ever goes (usually about 300 kilometers).

> to stay over the same spot on earth, a geostationary satellite also has to be directly above the equator

> Shuttle's orbit is always inclined to the equator by at least 28.5 degrees. Given this and the Shuttle's relatively low orbit, getting a satellite from its deployment orbit to its final geosynchronous orbit takes an Inertial Upper Stage (IUS) for a boost, and something called a Hohmann transfer.

a) Why does Hydrogen and Helium not exist in the earth's atmosphere?



b) Who first considered the utility of the geosynchronous orbit?