Facts & Figures About Asteroids and Comets

Facts & Figures About Asteroids and Comets

Some Facts and Figures about the Planets (As on August 17, 2022)

Asteroids

• Asteroids are also known as minor planets.

• They are objects that revolve around the Sun.

• They are mostly found between the orbits of Mars and Jupiter.

• They are a belt of debris that failed to assemble into planets and keeps on revolving around the Sun.

• This has come to be called as 'asteroid belt'.

• More than 5000 asteroids have been identified.

• Asteroids may be spherical, elongated, or irregular in shape.

• All asteroids rotate on their axis every 5 to 20 hours.

• Certain asteroids may have satellites.

• Trojan asteroids are found in two clouds moving in the orbit of Jupiter, one moving ahead of it and the other moving behind it.

• Scientists believe that these asteroids occupy a place where a planet could have existed but was prevented from forming by the disruptive gravitational force of the nearby giant planet, Jupiter.

Meteors and Meteorites

• Meteors and Meteorites are also called shooting stars.

• Meteors are fragments of rocks coming towards the Earth, formed due to the collision of asteroids with one another.

• Meteors are usually small, and due to the heat produced by air resistance, burn up before they reach the Earth's surface.

• When meteors are large and do not burn up completely, they land on the Earth's surface and are known as Meteorites.

• All meteorites are believed to originate in the asteroid belt, where a sudden collision may send them toward the Earth, and the Earth's gravity attracts them toward its surface.

Comets

Visitors of the Solar System, Comets (the name devel from the Latin words stella cometa meaning hairy star) are among the most spectacular and unpredictable bodies in the Solar System.

• Comets move around the Sun in regular orbits, but their orbits are elongated ellipses that take them hundreds and, sometimes, even thousands of years to complete one revolution around the Sun.

• Comets are made up of frozen gases that hold together rocky and metallic materials.

• A comet becomes visible only when it travels close to the Sun.

• It's ice melts, and the gas and dust are swept back into a tail.

• The tail always points away from the Sun.

• So when it is travelling away from the Sun, it is led by its tail.

Features of a Comet

• A comet is characterised by a long, luminous tail, which emits light.

• But this is visible only when the comet's orbit passes close to the Sun.

• When the comet travels close to the Sun, the ice melts to a head of gas called a Coma.

• The Sun's radiation sweeps this into a gas tail.

• Dust particles are also swept back to form a dust tail.

Stars

• Stars are heavenly bodies made up of hot, burning gases, thus shining by their light.

• Stars seem to be fixed concerning each other.

• They are in rapid motion but are at such a great distance that relative changes in position become noticeable only over the centuries.

• According to NASA, Proxima Centauri is the closest star to the Earth after the Sun.

• It is about 4.24 light years away.

• Pole star (or Polaris), Sirius, Vega, Capella, Alpha Centauri, Beta Centauri, Proxima Centauri, Spica, Regulus, Pleiades, Aldebaran, Arcturus, Betelgeuse, an,d of cour,se the Sun are some of the important examples of stars.

Facts about Stars

• There are billions and billions of stars in the sky, but only about 2000 stars can be seen with the naked eye on a clean, moonless night.

There are 1022 stars in the Universe.

• About 8000 stars are visible from Earth with the naked eye.

• Out of this, 4000 stars are visible in the Northern Hemisphere and 4000 in the Southern Hemisphere.

• In either hemisphere, only 2000 stars are visible at any given time.

• The other 2000 are located in the daytime sky, and the brightness of the Sun renders them invisible.

Constellations

• To enable astronomers to identify roughly the position of the stars, the sky has been divided into units.

• These units are known as Constellations.

• These constellations were named in honour of mythological characters.

At present, 88 constellations are recognized.

Some well-known Constellations (with Indian Names)

Some well-known constellations, with their Indian names, are given below:

Quasars

• A quasar is an extremely active and luminous type of active galactic nucleus (AGN).

• Quasars give off more energy than 100 normal galaxies combined.

• Recently, Astronomers identified the brightest quasar using the European Southern Observatory's (ESO) Very Large Telescope (VLT).

• The quasar, J0529-4351, is so far that its light took over 12 billion years to reach Earth.

• The black hole of the recently discovered quasar is growing in mass by the equivalent of one Sun per day, making it the fastest-growing black hole to date.

Earth's Galaxy: The Milky Way

• We live on the outer edge of a spiral-type galaxy called the Milky Way, which is about 1,00,000 light years in diameter and is rotating slowly.

• The Milky Way is a large spiral-shaped galaxy.

• It spans about 1,00,000 light-years across and is about 10,000 light-years thick at the centre.

• It is called the Milky Way because it appears as a soft, glowing light of billions of stars.

• These stars are so far that they can be seen only in a constellation, not separately.

• Galileo discovered that this band of light was produced by countless individual stars that the naked eye can not see.

• It takes about 250 million years to complete one revolution.

Andromeda: Earth's closest Galactic neighbour

• Andromeda is a spiral galaxy and also our closest neighbour.

• It appears as a fuzzy patch of light and contains millions of stars.

• It is the farthest object that can be seen with the naked eye.

• Along with the Milky Way, it belongs to a group of galaxies known as the Local Group, which in turn is a part of the Virgo Cluster of galaxies.

• Like stars, galaxies are grouped into clusters.

• Some clusters contain thousands of galaxies.

• About 30 galaxies, along with the Milky Way and the Andromeda, are grouped in one cluster called the Local Group.

• Clusters may group into upper clusters. Super clusters are also spread randomly throughout the universe.

Nebulae

• Nebulae are huge interstellar clouds of gas and dust that appear as faint, misty patches of light scattered all over the sky.

• They appear either as bright luminous clouds or as dark patches against a brighter background.

• A nebula depends for its luminosity upon the presence of stars that have either arisen from it or are contained in it.

• If the stars are extremely hot, the hydrogen in the nebula is ionized and emits a certain amount of light of its own.

• If a star is less hot, the nebula shines only by reflection.

• If there are no suitable stars, the nebula does not shine and remains dark, and can be detected only because it blots out the light of the stars beyond.

• There are five types of nebulous objects in the sky:

  1. Planetary nebulae

  2. Emission nebulae

  3. Reflection nebulae

  4. Dark nebulae

  5. Supernova remnants

Final Thoughts

Astronomy is not just about stars and planets — it’s about understanding our place in the vast universe filled with incredible and mysterious celestial bodies. From the rocky asteroids in the asteroid belt to the ice-rich comets with glowing tails, each object in space has its own story and role in shaping what we know about the cosmos.

We explored the difference between meteors, meteorites, and meteor showers, learned how stars shine with their light, and how constellations help us navigate the night sky. Objects like quasars, nebulae, and galaxies add even more depth to our understanding of space, showing us just how dynamic and alive the universe truly is.

With over 5000 identified asteroids, numerous types of nebulae, and structures like the Milky Way and Andromeda, the universe is a rich field of ongoing discovery. Each concept, whether it's a shooting star or a supermassive black hole, invites us to look deeper and wonder more.

This content provides a strong foundation in astronomy basics, designed to help students, learners, and curious minds grasp the beauty and complexity of outer space. Keep exploring, stay curious, and remember — the universe is full of answers waiting for us to ask the right questions.