One of the more spectacular phenomenon we see in the sky in the eclipse of the moon or
The term ‘Eclipse’ generally refers to when two objects align in the sky so one blocks the
other.(i.e., the moon can also eclipse a planet, one star can eclipse another etc..)
The path the moon take around the Earth occasionally crosses the ecliptic (path of Earth
around the sun). When this happens either the sun is blocked by the moon (solar eclipse)
or the moon is blocked by Earth (lunar eclipse)
The moon, which is orbiting Earth at about a 5 degree tilt actually passes directly across
the Earth – sun line at either a new moon or a full moon
At a new moon, the moon can block the view of the sun either totally (total solar eclipse) or
only a part of the sun (partial eclipse). These eclipses happen as the Earth passes through
a shadow cast by the moon on the Earth. The shadow is only however at most a couple of
hundred kilometers wide.
This is the path of totality where we will see a total solar eclipse. Since the moon is smaller
that Earth – this type of eclipse lasts at most a few minutes. One variation on this – the
moon changes distance from Earth. If it is at one of its further parts of the its orbit during
an eclipse it may not be big enough to totally cover the sun –annular eclipse.
http://en.wikipedia.org/wiki/Solar_eclipse Why don’t eclipses happen every new and full moon?
This is because the moon’s orbit around Earth is tilted at about 5 degrees from the Earth’s
orbit around the sun. Only when the moon cuts across the Earth – Sun line exactly at a
new or full moon can an eclipse happen. Generally the time between possible eclipse
alignments is every 56 months.
A series of eclipses will occur, moving from one pole to another over the space of a few
years, and then it will repeat over again.
•The path of the sun and moon and the pattern of eclipses as they move around actually
produces a regular repeated pattern called the Saros cycle.
This is a cycle of just over 18 years.
This is occurring as the different ways tomeasure the moons cycle over lap
o Synodic – new moon to new moon
o Anomalistic – perigee to perigee
o Draconic Node to node
Eclipses will occur at the same latitude, but not quite the same longitude, as the periods
are fractions, so there is an extra 8 hours.
Every 54 (and a bit) years, and eclipse should occur again in exactly the same location
since it will have cycled through a full day – this is the triple Saros cycle
Because eclipses at any one location happen infrequently, these are one of the hardest of
astronomical events to predict.
It takes a high level of astronomical sophistication to get a handle on the cycles in which
Only two ancient civilizations seemed to have a grasp of this eclipse cycle – these were the
Mayans and Babylonians (Chaldeans)
These two groups were also the only two ancient civilizations to develop a place keeping
Planet, Stars and Other Objects
Mercury, Venus, (Earth), Mars, Jupiter, Saturn.
These 5 are visible with the naked eye and have been known for millennia. The outermost 2 are Uranus, and Neptune. (Pluto’s designation has recently changed) have only been
discovered with the invention of the telescope.
To the ancients there were seven large bodies as the sun and moon were usually lumped
into the same category with the 5 visible planets.
Because these seven objects are all on the same plane in the solar system, they will seem
to follow a similar path against the background of stars. We call this line the ecliptic.
All of the planets orbit around the sun in the same direction, so their motion in the sky will
appear to travel in the same direction.
This moving chart shows the daily change of position of the sun against
the background starts. The planets also move along this path – though
there are some notable differences.
Venus and Mercury have orbits that are nearer to the sun. Because of this, they are never
seen very far from the sun – this means we see them only for at most a couple of hours
before sunrise or after sunset.
Venus will never appear higher than about 46 degrees above horizon, while Mercury, which
is even closer to the sun, appears at most 23 degrees above the horizon.
These planets also have a cycle of phases
Venus in particular is easy to observe with a telescope, as they align from Earth planet –
sun so that only part of the sunlit face is visible. These phases however cannot be seen