Department of Physics User's Guide to the Night Sky  How to
estimate the opposition position of a planet  The orbits of the
planets are only moderately inclined (i.e. a few degrees) to the
ecliptic plane and hence the planets are seen to roughly track
along the ecliptic. A good approximation to the Sun's (RA, Dec)
position is given by   RA [deg] = λ + 2.45 sin 2λ        sin Dec
[deg] = 0.4 × sin λ   ( or Dec [deg] = 23.5 × sin λ ) , where λ
is the Sun's ecliptic longitude. &lambda can be estimated by
assuming that the Earth's orbit is circular with the Sun
observed at λ = 0° on 21st March, λ = 30° on 21st April, λ = 60°
on 21st May, λ = 90° on 21st June, etc.  We can use these two
formulae to make a rough estimate of a planet's (RA, Dec)
position at the time of opposition. Jupiter was at opposition on
9th July 2008. So if we estimate the Sun's (RA, Dec) position at
a date six months eariler (or later), e.g. 9th January, then
this position will be approximately where Jupiter will be at
opposition.  On the 9th