Comets & Meteors

Astronomy’s not just about stars and planets. We’ve observed streaks of light that pass by when stargazing. Popularly called as shooting stars or falling stars and is associated with granting a wish in some cultures. Then there are these streaks of light with a visible bright head and a long tail that last in the same part of the sky for a longer duration. Yes! as the title reads, Meteors and Comets is what we are talking about.

What are Comets?

Comet Haley-Boppe. PC: Philipp Salzgeber

In general Comets are lumps of ice, dust, and rock that orbit the Sun. The typical comet has a core that is a few kilometres in diameter. Most of the comets that are seen having elliptical orbit with sun as its one centre. Some comets also have hyperbolic path. Comets mainly contains rock, ice, dust, carbon dioxide methane ammonia, hydrogen cyanide, . As a comet nears the Sun its ices will begin to heat up and turn into gases and plasma. These gases form a large glowing “head” around the comet that is called a “coma”. As the comet speeds through space, the gases will trail behind the comet forming a tail. Because of their coma and tail, comets appear fuzzy as they near the Sun. This allows astronomers to easily determine comets from other space objects. Some comets can be seen with the naked eye as they pass by Earth.

Comets are usually divided into two groups determined by the type of orbit they have:

• The first type of comet is the Short Period Comet. Short period comets have orbits of less than two hundred years. Some have very short orbits of just a few years. These types of comets originate from the Kuiper belt.
• The second type of comet is the Long Period Comet. Long period comets have orbits of greater than two hundred years. Some long period comets have orbits of thousands of years. Scientists think that long period comets come from the Oort cloud,

We know when we say comet the first word that comes to mind is Halley’s Comet which was last seen by many in the year 1986. However any comet that is visible to the naked eye and is bright is called a great comet. After Halley’s comet several great comets have visited the sun of which Hale–Bopp was visible in the region.

Comet ATLAS captured by Hubble Space Telescope after disintegration event

Comet SWAN as seen from the Southern Hemisphere – Photo copyright : Doug Ingram

Comets are also unpredictable. While we can certainly predict their orbit, their visibility is not something we can predict. Recently C/2019 Y4 or ATLAS Comet was expected to be visible to the naked eye but got disintegrated as it approached the sun and was not visible thereafter. Following ATLAS comet, Comet SWAN C/2020 F8 was visible in the southern hemisphere to the naked eye. Unlike a great comet, the Comet was faint and was expected to get brighter as it approached perihelion on May 27th 2020. However, as per data obtained by COBS (Comet OBServatory database), the comet started getting dimmer since May and is not visible to the naked eye.

Comets have been assigned the symbol and the Unicode ☄ which appears among emojis.

Science behind Comets

The Kuiper Belt

The Kuiper belt is a region of the Solar System that lies beyond the orbit of Neptune. It is much larger than the asteroid belt. The Kuiper belt contains millions of icy objects including some larger objects like the dwarf planets Pluto and Eris.

The Oort Cloud

Well beyond the Kuiper belt, scientists believe there is another collection of billions of comets called the Oort cloud. This is where long orbit comets come from. The outer limit of the Oort cloud defines the outer boundary of the Solar System.

What areMeteors?

A meteoroid is a small piece of rock or metal that has broken off from a comet or an asteroid. Meteoroids can form from asteroids colliding or as debris from comets speeding by the Sun. Meteors are meteoroids that get pulled into Earth’s atmosphere by Earth’s gravity. When a meteor hits the atmosphere it will heat up and burn with a bright streak of light called a “falling star” or a “shooting star.” If several meteors occur at the same time and near the same place in the sky, it is called a meteor shower. A meteorite is a meteor that does not entirely burn up and makes it all the way to the ground.

Comets leave behind dust and meteoroids in space which exist along their path long after they’ve passed away from us. Many comets have their paths intersecting with the Earth’s path around the Sun. This means during its orbit around the sun, Earth revisits this intersection point every year and it is during this point that we see the meteoroids become meteors in large number into what we call, a Meteor Shower. For example, The Leonid meteors take place when the Earth intersects the orbit of Comet 55P/Tempel-Tuttle, and the Perseid meteors happen when the Earth intersects the orbit of Comet 109P/Swift-Tuttle. Keeping in mind we are speaking about the Intersection of Orbits, these are just points in space through which Earth passes by and this is the reason why Meteor Showers last only for a short duration. As we move closer to these intersection points, the number of meteors seen increases, reaches a high number and then decreases.

Given the nature of orbits of the earth and the comet, we can visualize that these meteor showers will always appear to “radiate” (originate) from the same point in the sky. Since we associate each point in the sky to one of the 88 constellations, each meteor shower is named after the constellation that it appears to originate from. Hence Leonid meteor shower appears to originate from Leo consetllaion

Some of the important meteor showers visible in India

*Bold Meteor Showers are the bright meteor showers.

Other Prominent Meteor Showers

Meteor Visible on top as a streak, captured by members of PAAC

Some Facts about Comets and Meteors

• The Oort cloud is located about one light year from the Sun.
• One of the most famous comets is Halley’s Comet. Halley’s Comet has an orbit of 76 years and is visible from Earth as it passes by. It last passed by earth in 1986 and will revisit us in 2061.
• In the year 1910 when Halley’s comet visited the sun, earth passed through the comet’s tail
• During ancient times, people believed that the passing of a comet was an omen of doom.
• Eventually the ice will burn off of a comet and it will just be a metallic rock with no coma or tail. These comets are said to have gone “extinct”.
• Millions of meteors enter the Earth’s atmosphere every day. Most of them are about the size of a pebble.