Context: The Eta Aquariid meteor shower, which has been active since April 15, will peak on May 5 and 6. These showers are seen in May every year, and are best visible to countries such as Indonesia and Australia in the Southern Hemisphere.
Comets:
- Comets are frozen leftovers from the formation of our solar system, some 4.6 billion years ago.
- Comets are composed of dust, rock and ice, and orbit around the Sun in highly elliptical orbits which can, in some cases, take hundreds of thousands of years to complete.
- According to NASA, a total of 3,910 comets are currently known, although billions more are theorised to be orbiting the Sun beyond Neptune, in the Kuiper Belt and even more distant Oort cloud.
- Comets come in different sizes, although most are roughly 10 km wide. However, as they come closer to the Sun, comets heat up and spew gases and dust into a glowing head that can be larger than a planet. This material also forms a tail which stretches millions of miles.
Asteroids:
- Asteroids are rocky remnants from the early formation of our solar system (about 4.6 billion years ago) that mainly orbit the Sun between Mars and Jupiter.
- The asteroid belt is a nearly flat ring that contains millions of asteroids, ranging in size from less than 10 metres to 530 kms (The largest asteroid is Ceres, which is about one-quarter the size of Earth’s moon).
Meteoroids, Meteors and Meteorites:
- Meteoroids are rocky fragments of asteroids, comets, moons, and planetary collisions. They are much smaller than asteroids, ranging in size from tiny grains up to a metre. In our solar system, most meteoroids come from the asteroid belt, but a few come from comets and fragments of the Moon and Mars formed by impacts.
- Meteor is a flash of light (shooting star or falling star) seen when a meteoroid, asteroid, or comet heats up in the Earth’s atmosphere. Since most meteors are tiny (the size of a grain of sand) they completely burn up in Earth’s atmosphere. This burning also creates a brief tail.
- Meteorites are meteoroids that enter the Earth’s atmosphere and survive to impact the Earth’s surface. A large enough meteor can pass through the atmosphere and hit the Earth’s ground, often causing significant damage.
Eta Aquariid meteor shower:
- The Eta Aquariid meteor shower is formed when Earth passes through the orbital plane of the famous Halley’s Comet, which takes about 76 years to orbit the Sun once.
- Last seen in 1986, Halley’s comet is due to enter the inner solar system again in 2061.
- Like Eta Aquariids, the Orionids meteor shower is also caused by the Halley’s Comet, and appears every October.
- The Eta Aquariid meteor shower is known for its rapid speed. This makes for long, glowing tails which can last up to several minutes. The meteor shower consists of burning space debris moving at speeds of around 66 km per second (2.37 lakh kmph) into Earth’s atmosphere.
Southern Hemisphere: a better vantage point:
- The difference in meteor rates between the Northern and Southern Hemispheres during the Eta Aquarid meteor shower is primarily due to the position of this radiant point relative to each hemisphere.
- The radiant point of the Eta Aquarids (apparent origin of the meteors) is located near the star Eta Aquarii in the Aquarius constellation (in the southern part of the sky).
- From the Southern Hemisphere, this radiant is higher above the horizon, which means meteors appear to streak outwards in different directions and are more spread out across the sky.
- From the Northern Hemisphere, the radiant point of the Eta Aquarids is much closer to the horizon. This positioning causes the meteors to skim the Earth's atmosphere at a shallower angle. Consequently, they may appear as "Earthgrazers," which are long, slow-moving meteors that appear to skim or graze the surface of the Earth.
- Consequently, In the Southern Hemisphere, where the radiant is higher in the sky, observers can see more meteors per hour during the peak of the shower (around 30 to 40 meteors per hour). Conversely, in the Northern Hemisphere, with the radiant nearer to the horizon, observers typically see fewer meteors (around 10 per hour) and often in the form of Earthgrazers.