This page is devoted to defining some basic astronomical terms.
To find out when some of these will be visible from the UK, please see the Astronomical Events page
Conjunction
Occurs when two objects align in the sky and appear to be close together
Lunar Eclipse
Occur at full moon as it passes through the shadow of the earth. There are three types
- Total - when the moon passes fully through the umbra of the earth
- Partial - when the moon passes partly through the umbra of the earth and partly through the penumbra
- Penumbral - when the moon passes through the penumbra (little darkening occurs and may not be noticed)
Meteor Shower
Lines in the sky caused as the earth passes through small debris from comets which burns up as it enters the atmosphere. Usually named after the constellation they appear to come from e.g. Leonids from the constellation Leo
The shower can occur over several nights but has a Maximum when the number seen per hour is considerably higher, and it is that night that most amateur astronomers will watch. Depending on the exact time of the maximum compared to the earths rotation, it may not always be visible from the UK
Occultation
Occurs when the moon passes in front of an object
Penumbra
The shadow cast by the earth when it is partially obscuring the sun
Solar Eclipse
Occurs when the moon is directly between the sun and the earth. There are three types
- Total - when by coincidence the various distances mean that the moon appears to be the same size as the sun and therefore completely obscures or eclipses it
- Annular - when the moon is a little farther away and therefore smaller leaving a narrow ring of the sun visible round the moon
- Partial - when the alignment is not exact so the moon appears to take a ‘bite’ out of the sun
Depending where you are on the earth the same eclipse may appear to be total, annular or partial at different locations, or may transition between the types.
Transit
Occurs when Mercury or Venus, which are closer to the sun than earth, pass between us and the sun and are visible passing across the face of the sun
Umbra
The shadow cast by the earth when it is fully obscuring the sun