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A planet, by the International Astronomical Union, is defined as a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, but not massive enough to cause thermonuclear fusion in its inner core. The sun and the moon form part of our solar system. The sun is the largest object in the solar system and is mainly composed of 75% hydrogen and 25% helium by mass.
There are traces of heavier elements synthesized by past generators and are constituents of the inner terrestrial planets in the solar system while the jovian planets have compositions almost identical to the sun itself. The moon is the closest astronomical object to earth. This is also the only object that has been visited by man. Its mostly composed of rocks but has small iron-rich core. It lacks water and no permanent atmosphere. It has small traces of potassium and sodium. The new moon is the position when the earth, the sun, and the moon are roughly aligned.(Cumming, 2003)
Planets are generally divided into two main types: large, low-density gas giants and smaller, rocky terrestrials. Eight planets are orbiting around the sun. These are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Of late there are three dwarf planets in the solar system which are classified by the IAU: Ceres, Pluto and Eris. While the other eight are classified as the solar systems: Mercury, Venus, Earth, Mars, Jupiter, Saturn and Uranus, Neptune.
The inner planets that are near the sun are called the terrestrial or earth-like planets: mercury, venus, earth and mars. These are rocky with metal cores that have solid surfaces. The other outer planets ; Jupiter, Saturn, Uranus and Neptune are sometimes referred to as jovian or Jupiter-like. This is because they don’t have solid surfaces and are made mostly of hydrogen and helium. While the dwarf planet ceres is a crated ball of rock and are believed to be the largest object in the asteroid belt. Part of the Kuiper Belt is the planets Pluto and Eris which are frigid and icy worlds.(Cumming, 2003)
Other planets have rings in our solar system. These planets are those that are large and are Jupiter, Saturn, Uranus and Neptune. Saturn’s rings are the most magnificent; they are bright, wide and colorful. Uranus has nine dark rings around it, and Neptune’s rings are also dark, but contain a few bright arcs. Jupiter’s ring is thin and dark, and cannot be seen from Earth. Mercury, Venus, Mars, Jupiter and Saturn are visible without any kind of aid.
The planets Uranus and Neptune and the dwarf planets were discovered by the aid of telescopes. Apart from the above planets there are also comets, asteroids and meteors which are often grouped since they are all the same thing. That is; they are characterized by small pieces of rock and or ice that isn’t part of a major planet.(Cumming, 2003)
When the comets fly near the sun the high temperatures makes the ice to vaporize. Then the gas flies off the comet and with the help of solar radiation the dust particles are pushed away, forming a dust tail that can be many millions of miles long. This is seen with bare eye. These comets come from two places the Oort cloud and the Kuiper Belt. Comets from the Oort cloud have long orbital periods and can enter the solar system from any direction. The Kuiper belt is a ring of icy objects beyond the orbit of Neptune. Asteroids are small rocky objects in the solar system. An example is the ceres. These are found in the asteroid belt which is between Mars and Jupiter. Meteors the short, white trails across the sky that we normally refer as the shooting star. This are due to the inter-planetary dust that burn up when they slam into the earth’s atmosphere at high speeds. (Tanner, 2001)
Kepler’s law is three mathematical laws that describe the motion of planets in the solar system.
- The law of orbits: All planets move in elliptical orbits, with the sun at one focus. The elliptical shape of the orbit is a result of the inverse square force of gravity. The eccentricity of an ellipse can be defined as the ratio of the distance between the foci to the major axis of the ellipse. of the planetary orbits Pluto has a large eccentricity.
- The law of areas: A line that connects a planet to the sun sweeps out equal areas in equal times. This law which was discovered by Kepler arises from conservation of angular momentum. When the planet is closer to the sun, it moves faster, sweeping through a longer path in a given time. This explains why in the orbital there are sometimes when the planet is farther from the sun than other parts.
- The law of periods. The square of the period of any planet is proportional to the cube of the semi-major axis of its orbit. This law arises from the idea of gravitation.(Tanner, 2001)
Kepler’s Laws were derived for the planets that orbit the sun in the solar system and cable of working in any kind of situation.
This is so if one a discrete object with mass far greater than that any of the objects that orbit it.
Calculations for planets’ periods
We use Kepler’s third law to determine the orbital period, P.
Since P²=a³ since a is given by (r_perihelion + r_aphelion)/2
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where r_perihelion = earth orbital radius = 1AU
r_aphelion = mass orbital radius = 1.524AU
p = (1.262)3/2
= 518 days
A lunar eclipse occurs when the path of the earth blocks the light of the sun from reaching the moon. The moon then changes its color to dark reddish hue. This is so because of the light refraction. Since the size of the sun is bigger than the planet earth and sometimes sunlight bends around the surface of the earth and is refracted or bent, by the earth’s atmosphere. When this occurs, the blue light is removed and only the reddish hue remains. No more than three lunar eclipses occur in a calendar year.
Solar eclipse occurs when the path of the moon blocks the light of the sun from reaching the earth hence the earth is in the shadow of the moon. The earth becomes dark, and the sunlight is minimized and then the moon is seen with the sun’s corona surrounding it in the dark daytime sky. A lunar eclipse normally occurs at the full moon. The people who are on the night side of earth can see a lunar eclipse. While a solar eclipse can only occur during the new moon. In total there are no more than seven eclipses of any kind that can occur in a calendar year. (Tanner, 2001)
Moons in each planet
As of June 2007, there were 165 moons with four in the dwarf planets are Pluto, Eris and Ceres. Venus and Mercury are the only planets that don’t have moons. Earth and Eris have one moon each while Mars has two moons. Neptune which as a total of 13 moons with its largest moon called triton and also this planet has rings. Uranus has a total of 27 while Jupiter has the biggest number of moons that is 63. Saturn also is associated with rings as 59 moons.
Cumming, J. (2003), Contextualizing Authentic Assessment, Assessment in Education: Principles, Policy & Practice. London: Cambridge University Press.
Tanner, David E., Authentic Assessment: A Solution or Part of the Problem?, High School Journal; 2001. Vol 85 Issue 1, p24, 6p.