Tuesday, December 6, 2011
Monday, December 5, 2011
By the end of the International Astronomical Union (IAU) General Assembly on 24 August 2006 at Prague,the IAU therefore resolves that planets and other bodies,except satellites,in our solar system be defined into three distinct categories in the following way:
1.A planet is a celestial body that:
a) is in orbit is round the Sun,
b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assume a hydrostatic equilibrium (nearly round) shape,and
c) has cleared the neighbourhood around its orbit
The eight "planets" are Mercury,Venus,
Earth,Mars,Jupiter,Saturn,Uranus and Neptune.
2. A "dwarf" planet is a celestial body that:
a) is in orbit around the Sun
b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hdyrostatic equilibrium (nearly round) shape.
c) has not cleared the neighbourhood around its orbit.
d) is not a satellite
Solar system objects now classified as dwarf planets are,Ceres,Pluto,Eris,Makemake an Haumea.
3. "small solar system Bodles" referrd all other objects (solar system asteroids,most Trans-Neptunian Objects (TNOa),comets,and other small bodies axcept satellites orbiting the sun.
Sunday, December 4, 2011
Pluto is named after the Greek God of the under world. Pluto is the only planet in the Solar System which has not been visited by a spacecraft. The orbit of Pluto is the most elliptical of all the planets and in 1989 it was 'perihelion', when it come closer to the Sun than Neptune. Pluto is so small that it is only about one-sixth of the diameter of the Earth.
Characteristics of Pluto
Mass : 11.9421kg
Radius : 1,150 kg
Mean dansity : 2.0 g
Neptune is an apparent twin of Uranus internally, composed of hydrogen and helium, but with much more carbon, nitrogen, and oxygen than Jupiter and Saturn. The outermost of the four 'gas giant' planets, discovered in the year 1846 as a result of a prediction by the French astronomer Urbain Leverrier. There are at least 13 moons, including Triton, which has thin atmosphere, and Nereid
Characteristics of Neptune
1. Mass : 102.7 x 1024 kg
2. Radius : 24,750 km
3. Mean density : 1.7g/cm3
4.Rotational Period : 0.67 days
Saturday, December 3, 2011
Uranus is surrounded by a thick atmosphere of helium,hydrogen and methane.But unlike the other "cloudy" planets it has hardly any cloud markings. The most exciting thing about Uranus is the tilt of its axis.The axis is so tipped over that during its "year" the sun can shine almost overhead at each pole,and parts of its surface are bathed in continuosus day,and then continuous night,for almost 40 years.
Characteristics of Uranus
1. Mass :8.7 x 10 25 kg
2. Polar Radius : 25,500 km
3. Mean density : 1.3 g / cm3
4.Rotational Period : 17.2 h
5. Orbital period : 84.01 years
6. Mean distance from the Sun : 2.87 billion Km
Saturn used to be known as the planet with 'the rings'. Ring systems have now discovered around three neighbouring planets but Saturn's rings are by far the brightest. This planet rotates very fast but not faster than Jupiter and this rapid rotation causes it to bulge at its equator and flatten at its poles.
Rings of Saturn
The rings of Saturn were observed close up by Voyager sapcecraft.The rings have particle-size distribution ranging up to several meters.They are probably made of water ice-possibly created by break up of a moon which came too near Saturn.The rings show a complex structure including several divisions and innumerable 'ringlets".
Characteristics of Saturn
1. Mass : 5.69 x 1026 kg
2. Polar Radius : 53,500 km
3. Mean density : 0.69 g / cm3
4. Equatorial radius : 60,000 km
5. Rotational Period : 10 h 14 min
6. Orbital period : 29.5 years
7. Mean distance from the Sun : 1,427 million Km
Jupiter is the largest planet in the Solar System. It is so large that thousand Earths could fit inside it.But it spins so fast that its day is less than 10 hours long. This rapid spin has made its equator bulge outwards.
Moons of Jupiter
The Jovian moons number more than 60,including the four large satellites namely Callisto,Europa,Io,Ganymede discovered by Galileo,which are distinct worlds in themselves and lie in near-circular orbits in an equatarial plane.
Characteristics of Jupiter
1. Mass : 1.901 x 1027 kg
2. Radius : 66,750 km
3. Mean density : 1.33 g / cm3
4. Equatorial radius : 71,400 km
5. Rotational Period : 9 h 55 min 41 s
6. Orbital period : 11.9 years
7. Mean distance from the Sun : 778.34 million Km
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance.Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of Olympus Mons, the highest known mountain within the Solar System, and of Valles Marineris, the largest canyon. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature.Mars can easily be seen from Earth with the naked eye. Its apparent magnitude reaches −3.0 a brightness surpassed only by Jupiter, Venus, the Moon, and the Sun. Optical ground based telescopes are typically limited to resolving features about 300 km (186 miles) across when Earth and Mars are closest, because of Earth's atmosphere.
Characteristics of Mars
1. Mass : 6.24 x 1023 kg
2. Mean density : 3.93 g/cm3
4. Rotational Period : 24h 37min 22s
6. Mean distance from the Sun : 228 million km
7. Radius : 3,393 km
Earth formed 4.54 billion years ago, and life appeared on its surface within one billion years.The planet is home to millions of species, including humans. Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land.The physical properties of the Earth, as well as its geological history and orbit, have allowed life to persist during this period. The planet is expected to continue supporting life for at least another 500 million years.
Earth's outer surface is divided into several rigid segments, or tectonic plates, that migrate across the surface over periods of many millions of years. About 71% of the surface is covered by salt water oceans, with the remainder consisting of continents and islands which together have many lakes and other sources of water that contribute to the hydrosphere. Earth's poles are mostly covered with solid ice (Antarctic ice sheet) or sea ice (Arctic ice cap). The planet's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.
Earth interacts with other objects in space, especially the Sun and the Moon. At present, Earth orbits the Sun once every 366.26 times it rotates about its own axis, which is equal to 365.26 solar days, or one sidereal year. The Earth's axis of rotation is tilted 23.4° away from the perpendicular of its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt, and gradually slows the planet's rotation. Between approximately 3.8 billion and 4.1 billion years ago, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment.
1. Mass : 5.97 x 1024 kg
2. Radius : 6,378 km
3. Mean density : 5.52 g / cm3
4. Mean distance from the Sun : 149.6 million Km
5. Orbital period : 365.26 days
Friday, December 2, 2011
Venus is the planet that orbits the Sun between the Earth and Mercury, and is almost exactly the same size as the Earth. But it is very different from our planet. The surface of Venus is the hottest place in the Solar System, with a temperature reaching 4800c
It is rocky wind-swept planet with an 'atmosphere' that would feel thicker than ocean water at a depth of several hundred metres.
This atmosphere contains carbon dioxide, sulphuric acid and other poisonous compounds, and lightning flickers between the clouds.
Characteristics of Venus
1. Mass : 4.87 x 1024 kg2. Radius : 6,051 km
3. Mean density : 5.2 g / cm3
4. Equatorial gravity : 860 cm / s2
5. Rotational Period : 243 days (retrograde)
6. Orbital period : 224.7 days
7. Mean distance from the Sun : 108.2 million Km
4. Equatorial gravity : 860 cm / s2
5. Rotational Period : 243 days (retrograde)
6. Orbital period : 224.7 days
7. Mean distance from the Sun : 108.2 million Km
Mercury is the innermost and smallest planet in the Solar System,orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits. The perihelion of Mercury's orbit precesses around the Sun at an excess of 43 arcseconds per century, a phenomenon that was explained in the 20th century by Albert Einstein's General Theory of Relativity.Mercury is bright when viewed from Earth, ranging from −2.3 to 5.7 in apparent magnitude, but is not easily seen as its greatest angular separation from the Sun is only 28.3°. Since Mercury is normally lost in the glare of the Sun, unless there is a solar eclipse it can be viewed from Earth's Northern Hemisphere only in morning or evening twilight, while its extreme elongations occur in declinations south of the celestial equator, such that it can be seen at favorable apparitions from moderate latitudes in the Southern Hemisphere in a fully dark sky.
Characteristics of Mercury
1. Mass : 3.30 x 10 26 g
2. Radius : 2,439 km
3. Mean density :5.4 g / cm
4.Rotational period : 58.65 days
5. Orbital period : 88 days
6. Mean distance from the Sun : 57.9 million km
The Solar System
The world 'solar' means 'to do with the Sun'. The Sun and all the things in orbit around it make up the Solar System. It comprises a family of nine planets, most of which have one or more moons.Lost of other smaller objects, such as asteroids (minor planets) and comets, also travel around the Sun. The Sun, which is a star, is by far the largest body in the Solar System. The nine planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
The head of the Solar System
The Sun is a huge ball of hot gas. It is 150 million kilometres away from the Earth. Sun is an ordinary star, like the thousands of others you see in the night sky. Without it life is not possible on Earth. People on the Earth have always recognized the importance of the Sun and have often worshiped it as God.
Brightness of the Sun
To many astronomers who study quasars, pulsars, white dwarfs, red giants, black holes, and other exotic members of the Universe, the Sun is a fairly dull, average sort of star.
It is but one of one hundred thousand million stars in the Milky Way
galaxy, which is but one of the billions of galaxies in the Universe. It appears very bright to us only because it is by far our closest star, the next closest is Alpha Centauri which is more than 250,000 times further away.
Thursday, December 1, 2011
Tuesday, November 29, 2011
Asteroids are believed to have originated during the formation of the Solar System, when planetesimals accreted from solar nebula. The more primitive carbonaceous asteroids may have evolved little since then, while the other types may have been parts of larger bodies that first accreted and later broke up by collisions.
Recently a few small asteroids have been discovered in highly elliptical orbits that come inside the orbit of Mars, some crossing the orbit of the Earth - the Apollo, Amor, and Aten families.
Today a large number of asteroids are known.Around two thousand of them have well-determined orbits and revolve around the Sun as part of the 'main belt', in the gap between Mars and Jupiter.
They are tiny, only a handful having a diameter of more than a few tens of kilometres, and the combined mass of all the asteroids is thought to be only a fraction of that of the Moon.
Asteroids are the debris of planets that orbit the Sun. These are different sized chunks of rock,ranging from specks of dust to some which are a few hundred kilometres across.
Asteroids follow different orbits.In the eighteenth century, astronomers were convinced that a missing world existed between Mars and Jupiter.A search was mounted and the first asteroid, Ceres, was discovered in 1801.
Sunday, November 27, 2011
Meteors are the hot glowing pieces of rocks and dust from space that plunge into the Earth's atmosphere.Most meteors burn up above an altitude of 100km. If u gaze at the stars for half an hour on a clear bight,you will seen an occasional streak of light, which is a meteor's glowing trail.
Orbits of comets
Comets are believed to be left over particles from beginning of the Solar System,when most of these particles collided with each other to build up the planets. The comet nuclei, containing crumbly rock particles trapped in frozen ice, were left. If their orbits take them near the Sun, the heat turns the outer ice to vapour and solid particles are released as dust. In their frozen state far from the Sun, comets are invisible. Each time a comet passes near the Sun it pours some more of its nucleus into space. Eventually it 'dies' and becomes just an orbiting rock.
Halley's comet is the most famous of all comets, recorded by Chinese astronomers in 467 BC (and possibly in 611 BC). It is a periodic comet orbiting the Sun in a retrograde direction with a period of 76 years. It is named for the English astronomer Edmund Halley, who applied to comets Newton's theory of planetary motions and correctly predicted the return of the bright comet in the year 1758.
Comets are icy objects which travel through the Solar System. A bright comet in the night sky looks like a hazy patch with a long wispy tail. Comets travel in orbits through the Solar System.They evaporate gas and dust and grow long tails when they are near enough to the Sun's heat and light.
The tails always point away from the Sun, blown by the light and streams of atomic particles from the Sun. the most famous comet, Halley's Comets, can be seen from the Earth every 76 years.
We cannot see stars during the day because the Sun is too bright, but if we could we would notice the Sun slowly moving through the star patterns. It makes a trip right round the sky once a year, travelling through a band of constellations called the zodiac. The ancient Greeks divided the zodiac into 12 equal zones, called the 'signs' of the zodiac.
Each sign corresponds roughly to one of the zodiac constellations, through the official constellations that astronomers use are not all equal in size. People called astrologers make predictions about people's lives, based on the signs of the zodiac.
Groups of stars that make patterns in certain part of the sky are known as constellations. Some of them were named by the Greeks 2000 years ago, and Arab and Chinese astronomers had their own constellations too. There are 88 constellations and they cover the whole sky. They were probably invented as a way of referring to particular stars. Although the stars in a constellations appear to us to be in group, they are really vast distances away from each other.
Views of milky way
The Milky Way is a spiral galaxy with a nucleus of old stars surrounded by halo of much younger stars. the name given to the galaxy is because of its appearance like bright,creamy band of stars stretching across the sky when seen from the Earth.
The Area Of Milky Way
The diameter of the Milky Way is around 1,00,000 light years.It circles the whole sky which one can see wherever one is on the Earth. In the North, the constellations
( groups of stars) it goes through include
Auriga, Cassiopeia and Cygnus. Dark patches in the Milky Way are actually clouds of dust cutting out the light from the stars. The most famous one, 'the Coalsack', is in the Southern Cross.
Birth Of Stars
Stars are born and may shine for thousands of millions of years before they die. A cloud of gas and dust condenses to form a young star. Some massive stars,at the end of their life,explode as supernovae and could become black holes or neutron stars. Smaller stars at the end of their life,expand into red giants and then shirnk into white dwarfs that shine dimly.
Our Sun and all the stars you can see in the night sky belong to a giant family of stars that we call our Galaxy. It contains around 100,000 million stars.This Galaxy is known as the Milky Way. Beyond our own Galaxy, there are countless other galaxies scattered all across the space.