STEREO Orbits

 

Activity Part 3

 

In part 2 of the investigation we found which of the spacecraft had the Earth-Sun distance as its perihelion and which as its aphelion.

 

In part 3 we will find the distances of the perihelion and aphelion for each spacecraft.

We know two of the distance already (the ones that are 1AU) so we’ve got 2 more things to find out.

 

We will use the following formula(s) to help us:

 

 

 

 

 In these formulas –

 

The letter ‘e’ stands for eccentricity of orbit.  For a completely circular orbit the eccentricity is 0 (zero, as it isn’t eccentric at all), a very elliptical orbit will have an eccentricity of almost 1.

 

The letter ‘a’ stands for the ‘semi-major axis’, as in the diagram below:

 

 

We’ve actually illustrated 3 new terms here – ‘semi-major axis’, ‘major axis’ and ‘minor axis’.  Major and minor can be thought of as biggest and smallest distances whilst ‘semi-major’ means “half of the major axis”.

 

 For a simple help with this click here.

 For an advanced help with this click here.

 

We have already found the semi-major axes for each spacecraft in part 1 of this challenge so:

 

a_{(STEREO A)} = 0.961 AU

a_{(STEREO B)} = 1.043 AU

 

and

 

We have already found the aphelion, or major axis, for STEREO A as well as the perihelion, or minor axis, for STEREO B so:

 

Aphelion_{(STEREO A)} = 1 AU

Pereihelion_{(STEREO B)} = 1 AU

 

 

Using this information and the formulas we can now find all of the required information:

 

STEREO A

 

Aphelion

Perihelion

Eccentricity

 

STEREO B

 

Aphelion

Perihelion

Eccentricity

 

 

Check your answers by clicking here