<p>Here is a little picture. In such questions of geometric orbits, a picture helps greatly.</p>
<p><a href="https://i.sstatic.net/NG141.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/NG141.png" alt="enter image description here" /></a></p>
<p>The Earth is at point B, and the asteroid at opposition is at C, but at quadrature it is at point D.  Your first task is to work out the distances BC and BD.</p>
<p>Then the ratio of angular diameters is just the reciprocal of the ratio of distances.</p>
<p>This makes a couple of assumptions: the angular diameter is small (which it is) and the orbits are circlar (which is given for the asteroid and is a good approximation for the Earth.</p>

CC BY-SA 4.0
2023-04-10T10:05:32.683Z
2023-04-10T10:05:32.683Z
James K
<p>An asteroid is orbiting the Sun in a circular orbit of radius 4AU. Calculate the ratio of its angular diameters at opposition and quadrature.</p>
<p>I have tried using the idea of elongation but it does not work for me.</p>

CC BY-SA 4.0
2023-04-10T09:53:30.100Z
What do you mean by "the idea of elongation".  Did you try to work out how far the asteroid is from Earth at opposition and at quadrature.  That's the first step because angular diameter is inversely proportion to distance.
James K
CC BY-SA 4.0
2023-04-10T17:00:01.787Z
Check your definitions, e.g. here: http://astronomy.nmsu.edu/nicole/teaching/ASTR505/lectures/lecture08/slide09.html
Grimaldi
<astrophysics><orbital-mechanics>
Geocentric Planetary Configurations
happi07344
# Geocentric Planetary Configurations

(Asked by: username_0 on 2023-04-10)

An asteroid is orbiting the Sun in a circular orbit of radius 4AU. Calculate the ratio of its angular diameters at opposition and quadrature.

I have tried using the idea of elongation but it does not work for me.

**Tags:** astrophysics, orbital-mechanics
> **Comments:**
> **username_1**: What do you mean by "the idea of elongation".  Did you try to work out how far the asteroid is from Earth at opposition and at quadrature.  That's the first step because angular diameter is inversely proportion to distance.  
> **username_2**: Check your definitions, e.g. here: http://astronomy.nmsu.edu/nicole/teaching/ASTR505/lectures/lecture08/slide09.html  

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## 1 answers

### Answer by username_1 on 2023-04-10. Score: 3

Here is a little picture. In such questions of geometric orbits, a picture helps greatly.

[![enter image description here](https://i.sstatic.net/NG141.png)](https://i.sstatic.net/NG141.png)

The Earth is at point B, and the asteroid at opposition is at C, but at quadrature it is at point D. Your first task is to work out the distances BC and BD.

Then the ratio of angular diameters is just the reciprocal of the ratio of distances.

This makes a couple of assumptions: the angular diameter is small (which it is) and the orbits are circlar (which is given for the asteroid and is a good approximation for the Earth.


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