An eclipse is an event in space occurring when there is a celestial body or spacecraft partially or totally concealed within a period by moving into the shadow of another celestial body. This results in the alignment of three astronomical bodies which is known as a Syzygy.
Syzygy is the configuration of three or more astronomical bodies in a gravitational system aligned in a straight line.
The eclipse of a natural satellite or astronomical object orbiting a planet will occur when the object moves into the planet’s shadow. An eclipse can occur due to a complete obstruction (occultation) or a partial (transit) obstruction of the celestial body.
Occultation is a phenomenon whereby the body that is hidden is much smaller than the obstructing body, therefore the hidden body is not visible to the viewer due to total concealing—for example, the total obscuring of a star or spacecraft behind the moon.
Transit is the phenomenon whereby a large body, usually the sun or a planet, is obscured by a relatively small body in which the smaller body moves along the disk of the larger body and conceals only a small portion of it. For example, a planet such as Mercury occasionally transits the sun.
The type of shadow that is cast determines the type of eclipse that is being experienced. The shadow cast by the object during an eclipse can be divided into three distinct regions namely:
- Umbra – the dark centre portion of the shadow
- Penumbra – a partial type of shadow
- Antumbra
Umbra
An Umbra is the region of the shadow where the light source is entirely covered by the object and no light is seen. It is the dark central part of a shadow in which light is excluded and total occultation occurs. Therefore, the umbra of a circular object concealing a rounded body will give a circular shape. A total solar eclipse is caused by the moon’s umbra while full and partial lunar eclipses are caused by the Earth’s umbra.
Penumbra
Penumbra is the area of a shadow where the object only partially covers the light source. It is the portion of the shadow outside the dark central part formed by the celestial body when it only partially covers the light source. A viewer in a penumbra will observe a partial eclipse. A partial solar eclipse is experienced due to the moon’s penumbra and a penumbral lunar eclipse is caused by the Earth’s penumbra.
Antumbra
Antumbra occurs when the object is directly in front or within the disk of the light source but is too small to completely conceal it. It is the part that extends outside the tip of the umbra. A viewer in the antumbra region will experience an annular solar eclipse where the light from the source is visible around the occluding body. Then moving closer to the occluding body, its size gets bigger until a full umbra is observed.
Antumbra is only experienced whenever the object has a smaller diameter than the light source, this allows the outer rim of the light source to be seen around the body covering it. During an annular solar eclipse, an observer can view the rim of the sun’s disk around the moon as a ‘ring of fire’ while observing from the antumbra.
The two types of Eclipse
- Solar eclipse – eclipse of the sun
- Lunar eclipse – eclipse of the moon
Solar Eclipse
The solar eclipse is a type of eclipse that is experienced when the moon moves between the sun and the earth, thereby partially or totally concealing the light of the sun from a small region of the earth
The types of solar eclipse include Total solar eclipse, Partial solar eclipse, Annular solar eclipse and hybrid solar eclipse.
Click here for a detailed article on Solar eclipse and its types
Lunar Eclipse
A lunar eclipse is a type of eclipse that occurs when the moon enters into the shadow of the Earth. This makes the part of the moon that is overshadowed darkened. This only occurs when there is a full moon with the earth being between the moon and the sun
The types of lunar eclipse include Total lunar eclipse, penumbral lunar eclipse, Central lunar eclipse, Partial lunar eclipse and Selenelion.
