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See a shooting star shower this weekend

AUSSIE SKY-WATCHERS WILL HAVE THEIR GAZE fixed firmly on the sky this weekend, as one of the best meteor showers of the year puts on a display.

The Eta Aquariids shower will be best seen in the early morning hours, between about 3:30am and sunrise.

“The Eta Aquariids is one of the year’s best meteor showers for the Southern Hemisphere, partly because it is such a consistent shower, regularly producing bright meteors in the early morning for about a week, and also because it is well placed in our sky,” says Dr Tanya Hill, astronomer at the Melbourne Planetarium.

A meteor shower occurs when Earth passes through a clump of dust, or meteoroid stream, that’s orbiting the Sun. For the Eta Aquariids, the dust has been left behind by Comet Halley.

The Eta Aquariids meteor shower is can be seen in the early morning hours from late April to late May, but the best nights are May 5-8.

The Eta Aquariids meteor shower is can be seen in the early morning hours from late April to late May, but the best nights are May 5-8.

It takes about six weeks for Earth to cross completely through the stream, from mid-April through to late May. But we pass through the thickest part around May 5 to 8.

“The special thing about meteor showers is that all the meteors appear to come from the same part of the sky,” says Dr Hill, referring to what astronomers call the meteor shower’s ‘radiant’.

For the Eta Aquariids, the radiant is near the faint star Eta Aquarii, which at this time of the year rises in the east around 2:00am and is high in our northern sky by sunrise. (For our Northern Hemisphere readers, the radiant rises just a couple of hours before sunrise and remains much lower in the sky.)

“The higher the radiant in the sky, the more meteors can be seen,” says Dr Hill.

From a dark spot in a city location, you can expect to see perhaps one meteor every 5 or 6 minutes. From a dark country spot, perhaps one every 3 minutes.

You don’t need to have a telescope or binoculars. Just your own eyes is all you require.

Here are Dr Hill’s top tips for getting the most out of the meteor shower:

  1. Get comfortable. You’ll need to spend a considerable amount of time under the stars to catch the meteors. For example, it takes at least 15 minutes for your eyes to start to become dark adapted and allow you to notice the fainter meteors. That also means you should dress warmly.
  2. Find somewhere dark. Choose an observing spot away from street lights and with a good view of the entire sky. And don’t just look in the one spot. “While the meteors appear to radiate from near Eta Aquarii, they can travel quite a way across the sky,” says Dr Hill. “You want to be looking about 30 to 45 degrees to the left or right of the radiant — choose the direction with the least light pollution.”
  3. Watch with a friend. “Meteor observing is much more fun with family and friends around,” says Dr Hill. “That way there’ll be lots of oohs and aahs to share.”

Remembering Halley

This week marks the 25th anniversary of the launch of Giotto, the European Space Agency’s mission to Comet Halley.

Giotto was one of a small number of spacecraft sent to the famous comet, flying close by its nucleus and sending back remarkable, first-ever close-up images of a comet.

This video was released in 2006 to commemorate the 20th anniversary of Giotto’s encounter with Halley, and details the many extraordinary things that were learned.

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Famous comets are foreigners

Comet Halley

Comet Halley, and other famous comets, could have been "stolen" from other stars systems.

  • Comets formed within a cluster of stars
  • Sun captured comets when the stars dispersed
  • 90% could be from beyond the Solar System

Many of our Solar System’s most well known comets—including Halley, Hale-Bopp and, most recently, McNaught—could have been stolen from other stars, according to a new idea by an international team of astronomers.

The team used computer simulations to show that the Sun may have captured small icy bodies from its sibling stars when it was still young.

While the Sun currently has no companion stars, it is believed to have formed in a star cluster containing hundreds of closely packed stars that were embedded in a dense nebula of gas.

During this time, each star formed a large number of small icy bodies (comets) in a cloud from which its planets also formed.

Most of these comets were slung out of these young systems by the gravity of the newly forming planets, becoming tiny, free-floating ice balls in deep space.

The Sun’s star cluster eventually scattered, the individual stars going their own ways. The new computer models show that the Sun gravitationally captured a large cloud of comets as the cluster dispersed.

“When it was young, the Sun shared a lot of ‘spit’ with its siblings, and we can see that stuff today,” says lead author Dr Hal Levison of the Southwest Research Institute.

An artist's impression of the Oort cloud

An artist's impression of the Oort cloud, a swarm of comets that surrounds the Solar System.

90% of comets are foreigners

The scientists say this leads to the exciting possibility that the Sun’s current comet cloud contains a potpourri that includes material from a large number of the Sun’s infant stellar siblings.

Evidence for the scenario comes from the roughly spherical cloud of comets, known as the Oort cloud, that surrounds the Sun, extending halfway to the nearest star.

It has been commonly assumed this cloud formed from the flattened gas and dust cloud that surrounded the young Sun. However, because detailed models show that comets that formed as part the Solar System would have produced a thinner cloud than that known today, an extra source of comets is required.

Dr Levison says that “we can conclude that more than 90 percent of the observed Oort cloud comets” came from beyond the Solar System.

“The formation of the Oort cloud has been a mystery for over 60 years and our work likely solves this long-standing problem,” says Dr Ramon Brasser of the Observatoire de la Côte d’Azur, France.

Adapted from information issued by Southwest Research Institute / NASA.