Some Terms You Should Know: Finding the Planets

These are some terms you will come across in your lab class dealing with the planets.
Conjunction
When two objects have the same RA and Dec, they are in conjunction.  A planet is in conjunction with the sun will transit at local noon; this is a bad time to view the planet.
Click here for a pictures:  Inferior Planet  or  Superior Planet
Elongation
When an inferior planet is at its greatest angular distance from the sun in the sky as seen from Earth.  Since inferior planets can never be in opposition, this is the best time to view the planet.  Click here for a picture.
Inferior Planet
A planet whose orbit is smaller than that of the Earth.  Mercury and Venus are inferior planets.
Opposition
When a planet or other body is directly opposite the sun in the sky as see from Earth.  A planet in opposition will transit at local midnight; this is a good time to view the planet.  Click here for picture.
Retrograde Motion
The apparent backward motion of a planet compared to other objects in the solar system.
Superior Planet
A planet whose orbit is larger than that of the Earth.  Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto are superior planets.
Transit
To cross the meridian. An object on the meridian will be at the highest point it will reach in the sky.

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 This page was last updated on 18 January 1998
and is © 1998 by Jim McDonald.