Event driven astronomy
[5] The brilliant planet Venus in
conjunction with the Pleiades
open cluster.
[6] Planet Mars close to the open
cluster Messier 35 in Gemini.
[7] Venus transiting the Sun’s
disc in June, 2004.
[8] An annular eclipse of the
Sun photographed at the point
of maximum “annularity”.
The Moon's disc is perfectly
concentric within the larger disc
of the Sun. This is known as the
“ring of fire”.
As stated earlier, the apparent diameters of the Sun and Moon in the sky
are similar but subject to slight variation due to changes in distance between
the Sun and the Earth and the Earth and the Moon; these changes occurring
because the orbits concerned are elliptical rather than circular. If both the Sun
and the Moon line up in the sky there are three possible size combinations:ÁÁÁÁÁÁÁÁÁÁÁÁÁkÁÁ-A>Á&ͱͱGÁ:HH>:JKÁE:J@>JÁLA:GÁLA>Á,MG
ÁÁÁÁÁÁÁÁÁÁÁÁÁkÁÁ-A>Á&ͱͱGÁ:HH>:JKÁKF:EE>JÁLA:GÁLA>Á,MG
ÁÁÁÁÁÁÁÁÁÁÁÁÁkÁÁ-A>Á&ͱͱGÁ:HH>:JKÁ>P:<LEQÁLA>ÁK:F>ÁKBR>Á:KÁLA>Á,MGEvery body in the Solar System which is bathed in the Sun’s light casts
a shadow in the opposite direction. As the Sun is not a point source at the
distance of the major planets, the shadows cast take on a very specific three-
=BF>GKBͱG:EÁ?ͱJF ÁÁ=:JD
Á<ͱGN>J@BG@ÁKA:=ͱOÁ<ͱG>Á>PL>G=KÁ:O:QÁ?JͱFÁLA>Á
body surrounded by a diverging less intense region of shadow.
If you are in the dark central shadow cone and look back towards the
Sun, it would be completely hidden, none of its light managing to get to your
eyes. Outside of the dark cone in the diverging, less intense shadow, part of
LA>Á,MG KÁ=BK<ÁOͱME=Á;>ÁNBKB;E> Á-A>ÁBGG>JÁ=:JDÁ<ͱG>ÁBKÁDGͱOGÁ:KÁLA>ÁMF;J:EÁ
shadow while the outer, less intense region is known as the penumbral
shadow. From inside the umbral shadow, the Sun would appear totally
eclipsed while from within the penumbral shadow it would actually appear
partially eclipsed.
-A>ÁBGL>GKBLQÁͱ?ÁLA>ÁH>GMF;J:EÁKA:=ͱOÁBG<J>:K>KÁLA>Á<EͱK>JÁQͱMÁ@>LÁLͱÁ
LA>ÁBGG>JÁMF;J:EÁKA:=ͱO Á-ABKÁBKÁ;><:MK>ÁFͱJ>Á:G=ÁFͱJ>Áͱ?ÁLA>Á,MG KÁ=BK<Ádisc gives rise to what’s known as a "ring of fire". A more spectacular
form of solar eclipse occurs when the apparent size of the Moon’s disc
is greater than that of the Sun. If this occurs and you happen to be standing
in the right place at the right time, you’ll see the Moon’s disc completely
cover the Sun’s disc in an event commonly known as a total eclipse of
the Sun.
-A>ÁL>JFÁ>
to disappear from view. From this definition, an occultation can also be
described as an eclipse, as can the event which occurs when one body is
hidden by the shadow of another.
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