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PLANETS
Planet is a non-luminous celestial body illuminated by the light from a
star, such as the sun, around which it revolves. They are called light
reflecting members of the solar system. They are also called as
“wanderers” because their bodies seem to have meaningless and
aimless continuous motion around the sun. Their orbits are elliptical
and the same direction except for Uranus. Recently, a planet was
discovered by Dr. Josette Biyo, a professor from the Philippine
Science High School, Iloilo. The planet she discovered was named
after her.
Planets are always in rapid constant motion from a west to east directions.
They are kept in orbits by four natural forces, namely:
1. Centripetal force – the tendency of a rapidly whirling body to keep
itself toward the center. This force is such that the earth and the other
members of the solar system are kept from flying into outer space.
2. Centrifugal force – The tendency of a rapidly whirling body to recede
from the center. This is an outward pull. The planets are kept from
colliding with the sun among one another because the centrifugal force
contracts the gravitational pull of the sun.
3. Gravitational Pull of the sun – Gravitation is the attraction of one
body over any other body in the universe. The sun’s gravitational force is
enough to keep the resolving bodies around in their places.
4. Inertia of Motion – It is the tendency of a moving body to continue in
motion unless acted upon by an outside force. It keeps the earth and
other planets continuously revolving and rotating.
The nine (9) known planets of the solar system arranged in the order of their distance
from the sun are:
1. Mercury
- named after the messenger of the Greek Gods
- the smallest of the planets and closest to the sun
- the fastest moving planet
- 36,000,000 miles distance from the sun
- revolves around the sun in 88 days at the rate of 36 miles per hour
- 1965 radar echoes indicated that it makes one rotation on its axis in 58.6 earth days
instead
of the days in a west to east direction
- rotates around its axis only once during its complete revolution around the sun.
- due to the same length of revolution and rotation, it faces the sun only on one side,
such that
- the side facing the sun is always lighted and hot while the other side dark and cold;
- its diameter is only 50% greater than our moon, it resembles the moon more closely
than it
does to any of the other planets;
- its surface resembles the lunar surface and had no atmosphere.
- has a low reflecting power, returning only 7% of the light it receives;
- average temperature is about 6200 K
- active volcanoes have been noted in this planet and
- only 70% of this planet is visible to earth.
2. Venus
- named after the Greek Goddess of Beauty ;
- often called the morning star, when seen in the morning and evening star when seen
in the evening;
- brightest star in the sky, often fifteen times brighter than Sirius, the brightest star in
the winter sky.
- 67,000,000 miles from the sun; 26,000,000 from the earth;
- revolves around the sun in 7 ½ months or 225 days at the speed of 22 miles per
second;
- its diameter is 7,575 miles about 200 miles smaller than the diameter of the earth.
- sometimes called the earth’s twin because they have many similarities
- reflects about 60% of the sunlight it receives which accounts for its brightness;
- it has an atmosphere consisting of 10% carbon dioxide, 90% nitrogen and very little
water, the presence of oxygen has not been noted.
- atmospheric pressure is about 10 times that of the earth at sea level.
- its surface temperature is about 8000F;
- its cloud layers cover completely the planet from pole to pole;
- it passes through phases depending upon its position relative to the sun which may
indicate season;
3. Earth
- it is the third planet from the sun
- average distance from the sun is 93,000,000 miles;
- revolves around the sun in 365 ½ days, at the rate of 18 1/2 miles
per second;
- has an almost circular orbit;
- nearest to the sun in January (Perihelion) and farthest from the
sun in July (aphelion);
- rotates around its axis in 23 ½ degrees and
- it is the first planet from the sun to have a satellite which
revolves
around the earth in 28-30 days.
- the largest of terrestrial planets in the Solar System in terms of
diameter, mass and density
- it is referred to as the World, the Blue Planet and Terra
4. Mars
- named after the bloody Greek God of War
- reddish in color;
- 141,000,000 miles from the sun;
- revolves around the sun in 687 days and rotates on its axis in 24 hours and 37
minutes;
- its axis is tilted similar to the earth at about 23 ½ resulting in long summer days at
the polar regions when slanted towards the sun and long winter nights when tilted
away from the sun.
- it is the only planet which comes closest to the earth;
- according to Mariner II, its has no carbon dioxide in it’s atmosphere and no
magnetic field
- it is smaller in size and mass than the Earth or Venus; and its diameter is about ½
that of the earth;
- has sufficient gravitational attraction at its surface to retain a thin temperature;
- receives only 43% per square mile of heat, therefore, its temperature is lower than
the Earth’s;
- has a very low atmospheric pressure, lacks oxygen, little water and has extreme
changes in temperature;
- when viewed through a telescope, it has also a white polar cap
5. Jupiter
- named after the Olympian Gods,
- 483 million miles from the sun and 367 million miles from the earth,
- its diameter is 88,000 miles,
- a super space ship from the earth would take 200 years to reach its
ray of light
- Traveling at the speed of light (186,000 miles per second) would be in
Jupiter in one hour.
- it is the largest planet, its mass is bigger than all the planets combined;
- a good reflector of the light from the sun;
- receives only about 1/25 as much heat and light compared to the earth.
- rotates on its axis in less than 10 hours;
- has flattened poles, bulging equator and cloud hands in its atmosphere
due to its fast rotation
- its equator is 6,000 miles greater than the poles.
- the temperature at its surface is 2000F below zero, while at the visible
cloud layers is minus 1600F.
- its atmosphere contains great quantities of ammonia; methane, hydrogen
and helium
- has 12 satellites.
6. SATURN
- named after the father of the ruler of the gods because of its slow pace;
- most distant of the bright planet; second largest planet on the solar system;
- 886 million miles away from the sun and about twice as far away from the earth as
Jupiter;
- revolves around the sun in 30 years at the rate of 6 miles per second;
- rotates on its axis about 10 hours; flattened at the poles and bulging at the equator
as a result of its fast rate of rotation;
- its axis is tilted more than of the Earth so that it has a very long season with a very
short days; its period of day light is only 3 hours;
- its atmosphere resembles Jupiter though more extensive; at the lower temperature,
ammonia seems to be frozen while methane is more prominent in the spectrum;
- its density is about seven tenths than of water and therefore has the lightest
average density;
- has three beautiful rings; discovered by Cassini, which are continually whirling
around; and which disappear completely once every 15 years; believed to be
particles of dust or gravel or even show collected into balls that move around the
planet; and;
- has ten satellites whose diameters vary from 200-2,600 miles.
- Titan is the largest, most unique and brightest of all its satellites; it is also the only
known satellites with an atmosphere.
7. URANUS
- named after the grandfather of Jupiter;
- first planet to be found since ancient times
- first to be discovered by William Herschel in the constellations of
Gemini;
- 1,782, 000 miles away from the sun;
- revolves around the sun in 84 years at the rate of 4 ½ miles per second;
- has a diameter of about 30,000 to 32,000 miles;
- rotates on its axis in 11 hours;
- has an atmosphere showing the presence of methane, hydrogen, helium,
and ammonia which are frozen due to very low temperature.
- has 1 ½ times the density of water.
- the surface temperature is 3400F below zero;
- has five known satellites whose diameter range from 500 to 100 miles
and;
- revolve in a retrograde orbit together with its satellite and the direction of
revolution is from east to west.
8. NEPTUNE
- named after the god of the sea
- discovered by young German, Johann G. Galle, in Berlin in 1886;
- 2,880,000,000 miles distant from the sun, and a million miles from
Uranus;
- revolves around the sun in 165 years at the rate of 3 miles per
second;
- has the same size and mass as Uranus, while its diameter is 31,000 miles;
its density is 2 ½ times that of water;
- it has two known satellites.
9. PLUTO
-named after the god of the underworld;
- the planet was discovered in the constellation of Gemini, from the
photographs made by Clyde Tombaugh in 1930.
- 3,720,000,000 is its estimated distance in miles from the sun and
is about 40 times the distance between the earth and the sun;
- revolves around the sun in 250 years;
- traces of ammonia is believed to be found in it but maybe frozen.