Shishu Sansaar | Science
List of Eclipses | Eclipses | Lular Eclipse
Eclipse means hiding. Thus in Solar Eclipse, the Sun is hidden from our eyes, and in Lunar Eclipse the Moon is hidden from our eyes. What is the reason of their hiding on certain days? There are some facts about them.
1. Solar Eclipse is always on New Moon day, and Lunar Eclipse is always on Full Moon day.
Types of Solar Eclipse
Total Solar Eclipse is rare, so if you get an opportunity to look at it, never miss it, it is really interesting to see and experience a total Solar Eclipse. To see a total Solar Eclipse you have to be in the path of totality, and this path, sometimes 200 miles wide, never covers more than roughly 1/2% of the 1% area of the whole earth and often traverses upon seas or remote regions of the planet. Only fewer than 70 total Solar Eclipses occur in a century - this makes a chance for seeing a total Solar Eclipse for most of us only once in lifetime.
DON'T FORGET TO USE SUNGLASSES WHILE LOOKING AT A Solar Eclipse
It is quite remarkable that the total Eclipse occurs at all. The Sun whose size 400 times larger than that of the Moon, happens to be about 400 times as far away from the earth. This condition permits just barely cover up the Sun. In fact, if the Moon's diameter (2,160 miles or 3,476 Kilometers) were just 140 miles (224 Kilometers) shorter than this, it could have never caused the total Solar Eclipse.
When Does It Occur?
If the Lunar nodes are stationary with respect to the stars, each node would be lined up between the earth and the Sun at the same time each year, the Eclipses would have occurred at the same time each year - every six month. But this is not so, because the nodes of the Lunar orbits shift their orientation gradually. Since the Moon's orbit is tilted 5 degree from the earth's orbit, normally it passes either below or above the line between the Sun and the earth. It is only about every 6 months the conditions are favorable for any Eclipse.
This alignment happens 18.6 days sooner than if the nodes have not been shifting, creating the shorter Eclipse year (normal Eclipse year = 346.6 days). This phenomenon determines the pattern of Eclipses. This change makes it happen earlier and earlier than before.
How Often It Occurs?
There will be 18 Solar Eclipses between 1996 and 2020. The common perception that the Eclipses are infrequent is because the observation of a total Eclipse from a given point of the earth is not common, for example, it will be two decades before the next total Solar Eclipse will be visible in North America. The last total Solar Eclipse was on August 11, 1999.
Total Solar Eclipses in India
(10) 2114, Jul 3 Total Solar Eclipse in North India
- after nearly 105 years from the last Total Eclipse (2009)
Patterns of Solar Eclipses
We have a new Moon every month, but we donít have an Eclipse every month. Usually the Moon's shadow passes completely above or completely below the Earth. This is because the Moon's orbit is tilted at about a 5-degree angle to the Earth's orbit, so that the Moon usually passes above or below the direct line of sight between the Earth and the Sun.
Only at those times when the New Moon is near one of its nodes can a Solar Eclipse occur. (The nodes are the two points where the Moonís orbit intersects the plane of the Earthís orbit, the ecliptic). For a Solar Eclipse to occur, the new Moon must be close enough to the ecliptic plane so that itís shadow will touch some part of the Earth. As it turns out, when the New Moon appears within 18-3/4 days before or after the alignment of a node, a Solar Eclipse will take place. This creates a 37-1/2-day time window for Eclipse, called an Eclipse season, when the conditions are favorable for an Eclipse to occur.
If the Lunar
nodes were stationary with respect to the stars, each node would be lined
up between the Earth and the Sun at the same time each year, and Eclipses
would occur at the same two periods of time, every year, six months apart.
In fact, this is what almost happens, except that the nodes of the lunar
orbit are gradually shifting their orientation in space. By the time one
node is in line with the Sun again, it has regressed slightly. The
alignment happens 18.6 days sooner than if the nodes were not moving,
creating the shorter Eclipse year (about 346.6 days). This regular
regression of the Moonís nodes is the other cycle that determines the
patterns of Eclipses over time.
cycles Ė the Lunar month (or Synodic month) and the Eclipse year Ė plod
along year after year without much apparent coincidence. An Eclipse year
(346.62 days) does not come close to being an exact multiple of these
periods (324.83 days in 11 Synodic months, 354.36 in 12). A longer cycle,
close to an exact multiple of these two periods, would be useful for
making Eclipse predictions.
This resonance between the periods of these two cycles produces a repetition of Eclipses in a remarkably short time. (In terms of astronomical cycles, 18 years is a short time) The paths of totality for successive Eclipses in this Saros series change in a regular pattern every 18 years. The paths, which are similar in shape, gradually widen and shift to more northerly latitudes. The longitude for each successive Eclipse in the series shifts to the west a little more than one third of the way around the globe.
A series of Eclipses, each separated by this 18-year 11-1/3-day cycle, is called a Saros series. Because the resonance between 19 Eclipse years and the Saros is not exact (0.46-day difference), a Saros series cannot go on indefinitely. Eventually a series reaches a point when the Eclipses are no longer visible; the umbra passes too far above or below the Earth to be seen. A single Saros series spans over 1,200 years and includes between 68 and 75 Solar Eclipses.
The repetition of Eclipses follows very regular patterns in time. Eclipse seasons and Saros cycles come and go like clockwork. The repetition of Eclipses at a given place on the Earth, however, appears to follow no discernible cycle. Partial phases of Solar Eclipses can be seen about every 2-1/2 years from any particular spot on the Earth. The best estimate for total Eclipses is to say they recur at the same location about every 360 years on the average. This figure is based on the average area of the paths of totality, the total surface area of the Earth, and the overall frequency of total Eclipses. But because we are dealing with averages over the time span of many millennia, the actual circumstances for particular locales vary, sometimes widely, from this estimate. For example, the Moonís umbra never passed over the city of London during a period of 837 years between consecutive total Solar Eclipses in the years 878 and 1715. On the other hand, if you visit the coast of Angola in southern Africa to witness almost 5 minutes of a total Eclipse on June 21, 2001, you can return to the same spot three Eclipse seasons later for two minutes of totality on Dec. 4, 2002.
Created by Sushma Gupta on January 15, 2002
Modified on 09/23/13