Solar system in stamps

An interesting set of 10 stamps released by the Philatelic Bureau on 5 December 2014 features the solar system. It is attractively printed and the value of each stamp ranged from Rs. 7 to Rs. 40.
The 10 stamps depict the Sun, the Moon and the eight planets. The eight planets on elliptical objects around the Sun in increasing distance from it are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The Moon orbits around the Earth.
The Stamp Bulletin (858) explains each stamp in detail. The text has been developed by Dr Karan Ratnatunga and Anura C. Perera.
The solar system comprises the Sun and the objects that orbit it, whether they orbit it directly or by orbiting other objects that orbit it directly. Of those objects that orbit the Sun directly, the largest eight are the planet that form the planetary system around it, while the remainder are significantly smaller objects, such as dwarf planets and small Solar System bodies (SSSBs) such as comets and asteroids.
The fascinating story of the solar system dates back to the distant past. To begin with, the humans identified the Sun, the Moon and the five planets – Mercury, Venus, Mars, Jupiter and Saturn – as gods that appear to move relative to the stars, through a band of constellations in the sky known as the Zodiac. The seven days of the week were identified with these god-like objects in the sky.
As time went on, they accepted that these were not gods but bodies like the Earth. Aristotle believed that all these objects including the sun orbit round the Earth. In 1543, the Polish astronomer Nicholas Copernicus argued that this belief was wrong and that the planets including the Earth, orbit round the Sun.
Currently 172 moons have been recognised in the solar system. These orbit the planets beyond the Earth. Our Moon orbits around the Earth.
Between the orbits of Mars and Jupiter there are countless smaller objects known as asteroids that orbit round the Sun. The first of these was discovered in 1801 and was named Ceres and is considered as the largest asteroid. Pluto, discovered in 1930, became the most distant planet known to orbit the Sun. These two are now defined as dwarf planets of which an increasing number are being discovered beyond the orbit of Neptune.
Astronomers have determined that the solar system including the Sun, planets, moons and asteroids condensed out of a large cloud of interstellar gas and dust about 4.6 billion years ago.
At the speed of light which is about 300,000 km per second it takes 500 seconds for light from the Sun to reach the Earth. The distance from Earth to Sun of about 150 million kilometres is defined as an Astronomical Unit (AU) and used to measure distances within the Solar System.
The Sun with a physical diameter of 1.4 million km is visible from the Earth as an extremely bright disk with an angular diameter of about half a degree. Said to be 4.6 billion years old, it is a medium-sized yellow colour star, located in our outer spiral arm of our Galaxy known as the Milky Way. It has an expected lifetime of another five billion years.
Mercury is the planet closest to the Sun. Though visible to the naked eye it is somewhat difficult to see. It is the smallest among the eight planets with a diameter of 4,880km – less than half of the diameter of the Earth or 1.5 times larger than the Moon. It is a rocky planet with a solid crated surface.
Venus is the brightest object other than the Moon in the night sky and the most familiar to many. When visible at dawn it is called the ‘morning star’ (‘udaa tharuva’) and at dusk as the ‘evening star’ (‘irabatu tharuva’). It is our closest neighbour among the planets. Its diameter is 95% of that of the Earth. It is a rock planet covered by a thick layer of clouds.
The Earth, according to Roman mythology, is held on his shoulders by a giant called Atlas. The Hindus believed that four elephants on the back of a giant tortoise bear the Earth held it. The Chinese belief is that a flat Earth rests upon a giant dragon. The Earth rotates round its axis from west to east once in every 24 hours causing night and day. The Earth, which moves with an orbital speed of 30km takes 365.24 days to complete one orbit, i.e Earth year, at an average distance of 150 Million km.
The Moon, which orbits the Earth at an average distance of 384,000km, has a physical diameter of 3,476km. Its sunlit surface is seen as a crescent to full phase, with an apparent angular diameter about half a degree. It is the brightest object in the night sky. It takes 27.3 days for its elliptical orbit of the Earth.
About 400 years ago, Galileo observing the Moon through his telescope, was able to recognise craters, mountains, flat lands, rocks, etc. on the surface. Between 1969-’72, 12 astronauts landed on the Moon under USA’a Apollo program and brought back rocks for detailed scientific analysis.
Mars is the first planet outside the Earth’s orbit. It looks red to the naked eye. Smaller than the Earth, it has a diameter of 6,780km. Mars is a rocky planet and is considered a habitable place. No evidence of life has been found by automated rovers, which have landed and explored the surface for many years.
Jupiter is the largest planet of the Solar System with a volume 1,321 times larger than the Earth. It is a gas giant with a temperature as much as 35,000 Celsius and its core if of dense metallic hydrogen. Jupiter even emits radio waves. Its atmosphere is found to be full of toxic gases such as hydrogen helium and solid ammonia.
Saturn is considered to be the most attractive planet of the solar system. To Romans it was the god of cultivation. Through his telescope a Dutch astronomer, Christian Higens observed the beautiful rings around Saturn and identified Titan, its largest moon. Also a gas giant, Saturn is the second largest planet of the solar system with a volume815 times that of the Earth.
Uranus was discovered in March 1781 by an amateur astronomer, William Hershel – the first since antiquity. It was named Uranus, the Greek god personifying the sky. With an orbit speed of 6.8kms, it takes 84 years to orbit the Sun. Due to its distance from the Sun, very little sunlight falls on it. It is a gas giant and has an atmosphere containing ammonia, methane and hydrogen.
Neptune, bearing the name of the gold of the ocean of the Roman pantheon, was discovered in September 1846, is not visible to the naked eye. It can be observed through a good telescope as a green disk with an apparent angular diameter of just over two second of arc. It is a gas giant with a snow-covered surface made of water, ammonia and methane. It is affected with constant violent storms and winds and emits radio waves.