Indira Gandhi Planetarium, Lucknow Veer Bahadur Singh Planetarium, Gorakhpur        Aryabhatt Planetarium, Rampur


Asteroids, also called as minor Planets or Planetoids, are rocky and metallic objects that orbit the Sun but are too small to be considered as planets.Asteroids vary greatly in size. The largest and first known asteroid, Ceres, was discovered in 1801. It is 580 miles (933 kilometers) in diameter. Ceres is believed to contain about 1/3 the total mass of all the Asteroids. One of the smallest, discovered in 1991 and named 1991 BA, is only about 20 feet (6 meters) across.


According to International Astronomical Union, a solid object moving in interplanetary space, of a size considerably smaller than an Asteroid and considerably larger than an Atom is called as METEOROID. Size of a meteoroid is between 100 µm and 10 m across. Very small meteoroids are known as micrometeoroids. A meteoroid is a piece of stony or metallic debris which travels in outer space. Meteoroids travel around the Sun in a variety of orbits and at various speeds. The fastest meteoroids move at about 42 kilometers per second. Most meteoroids are about the size of a pebble.


When an Asteroid enters the Earth's atmosphere, friction between that asteroid and atmospheric gases heats it to the point that it glows and becomes visible to our eyes. This streak of light in the sky is known as a METEOR. Most meteors glow for only a few seconds prior to burning up before hitting the Earth's surface.People often refer to meteors as falling or shooting stars. The brightest of the meteors are called fireballs. A METEOR SHOWER is a celestial event in which a number of meteors are observed to radiate from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Intense or unusual meteor showers are known as METEOR OUTBURST or METEOR STORM, which may produce greater than 1,000 meteors an hour.


A meteorite is a portion of a meteoroid or asteroid that survives its passage through the atmosphere and impact with the ground without being destroyed.Over 100 meteorites hit the Earth each year. Fortunately, most of them are very small. There are three main types of meteorites. The most abundant are Stone Meteorites which are primarily made up of silicate minerals such as olivine, pyroxene and feldspar. The second, Iron Meteorites, are mainly composed of iron but also contain a significant amount of nickel. The rarest of the three are the Stony-Iron meteorites. They are a mixture of stone and metallic materials.


Comets are small, fragile, irregularly shaped bodies composed of a mixture of non-volatile grains and frozen gases. They have highly elliptical orbits that bring them very close to the Sun and swing them deeply into space, often beyond the orbit of Pluto. It is made up of a nucleus (solid, frozen ice, gas and dust), a gaseous coma (water vapor, CO2, and other gases) and a long tail (made of dust and ionized gases). The tail develops when the comet is near the Sun. Its long ion tail of always points away from the sun, because of the force of the solar wind. The tail can be up to 250 million kms long, and is most of what we see. Comets are only visible when they're near the sun in their highly eccentric orbits.


 Region within the orbit of Neptune is known as Cis-Neptunian Region and the objects within this region are referred to as Cis-Neptunian Objects. Cis-Neptunian objects includes the planets, their moons, traditional asteroids and all other sub-planetary bodies orbiting the Sun at or within the distance of Neptune, but outside the orbit of Jupiter. This includes the icy asteroids known as Centaurs and the Neptune Trojans.


The area beyond the planets is generally referred to TRANS-NEPTUNIAN REGION. This region is sometimes known as the "outer Solar System”. This region is broadly classified into two sub-regions as-

• Kuiper Belt

 • Scattered Disc


 The Kuiper belt also called as the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending from the orbit of Neptune at a distance of 30 to 55 AU from the Sun. It is similar to the asteroid belt, although it is far larger—20 times as wide and 20 to 200 times as massive. The objects within the Kuiper belt are referred to as Kupier Belt Object(KBO). More than 70,000 KBOs over 100 kms in diameter are believed to exist. Pluto is the largest known member of the Kuiper belt.


The scattered disk is a subset of trans-Neptunian Objects which is overlapping the Kuiper belt but extending much further outwards. The objects within this region are known as Scattered Disc objects. The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects known as the Kuiper belt, but its outer limits reach much farther away from the Sun. The largest of Scattered Disc Objects is ERIS, discovered in 2003,which has been classified as a dwarf planet too.


 The physical space outside the solar system and within a galaxy which is not occupied by stars or their planetary systems is referred to as Interstellar Space or the farthest region of the solar system. This region is further classified as:

• Heliosphere

 • Oort cloud



The heliosphere is the immense magnetic bubble contained in solar system which is blown into the interstellar medium by the solar wind. The density of particles in the heliosphere is very low.The HELIPAUSE is the name for the blurred boundary between the heliosphere and the interstellar gas outside the solar system. As the solar wind approaches the heliopause, it slows suddenly, forming a shock wave.


The giant cemetery sphere surrounding the solar system is called as Oort cloud, named after the scientist JAN OORT who postulated its existence in 1950. The oort cloud is an immense spherical cloud surrounding the planetary system and extending approximately 3 light years from the sun. This vast distance is considered the edge of the sun's orbit of physical, gravitational, or dynamical influence. The Oort cloud is thought to comprise two separate regions: A Spherical Outer Oort Cloud and A Disc-shaped Inner Oort Cloud, or Hills Cloud. Objects in the Oort Cloud are largely composed of ices, such as water, ammonia and methane.

SEDNA or 90377 SEDNA:

The most distant object orbiting the sun is SEDNA or 90377 SEDNA (90377 is the MPC designation i.e. Minor Planet Center Designation). It's a mysterious planet-like body three times farther from Earth than Pluto. . However, its farthest orbital distance from the Sun is estimated to be 960 AU and so it is the most distant known object in the Solar System.Roughly two-thirds the size of Pluto, Sedna is hypothetically large enough to be rounded by its own gravity, and thus would qualify as a dwarf planet under current definitions.