{"id":30847,"date":"2022-04-08T08:14:29","date_gmt":"2022-04-08T08:14:29","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=106938"},"modified":"2022-04-08T08:27:12","modified_gmt":"2022-04-08T08:27:12","slug":"a-beginners-guide-to-asteroids","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/a-beginners-guide-to-asteroids\/","title":{"rendered":"A beginner\u2019s guide to asteroids"},"content":{"rendered":"

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By Anton Vamplew\n \t\t<\/p>

Published: Friday, 08 April 2022 at 12:00 am<\/p>

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For a long time, when we only had eyes to survey the heavens, the Solar System was a nice and simple place.<\/p>\n

Back then just five big planets, the Sun and our Moon moved around the sky, along with the odd infrequent visiting comet.<\/p>\n

Things changed with the invention of the telescope, because we could now peer into the dark with instruments that allowed us to see smaller, fainter objects.<\/p>\n

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An image of asteroid 433 Eros\u2019s southern hemisphere, where the NEAR Shoemaker spacecraft touched down. Credit: NASA<\/span><\/figcaption><\/div>\n

Nevertheless, and quite incredibly, it was still approaching 200 hundred years after Galileo<\/a> first pointed his scope skyward before the first asteroid was discovered.<\/p>\n

The Near Earth Asteroid Rendezvous was the first spacecraft to orbit and later land on an asteroid.<\/span><\/p>\n

After its launch in February 1996, the craft entered orbit around asteroid 433 Eros<\/a> in February 2000 and landed one year later.<\/span><\/p>\n

And now missions like the Japanese Hayabusa2<\/a> and NASA\u2019s OSIRIS-REx<\/a> are returning pieces of asteroids to Earth for study.<\/p>\n

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A view of asteroid Bennu, captured by OSIRIS-REx\u2019s OCAMS (MapCam) instrument on 28 April 2020 from a distance of 10km. Credit: NASA\/Goddard\/University of Arizona<\/span><\/figcaption><\/div>\n

The official International Astronomical Union, which is involved in the naming of asteroids (for example, there are asteroids called Flora, Hilda and Albert), also decides overall what they will be classed as.<\/p>\n

The IAU has now officially designated asteroids as being in the Small Solar System Bodies category, along with everything else that isn\u2019t a planet or a moon.<\/p>\n

However, the use of the word \u2018asteroid\u2019, or alternatively \u2018minor planet\u2019, continues, not least because the official name is rather dull.<\/p>\n

What is an asteroid?<\/strong><\/h2>\n
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Radar images of asteroid 2016 AJ193, Goldstone Observatory, 3 September 2021. Credit: NASA\/JPL-Caltech<\/span><\/figcaption><\/div>\n

So, what is an asteroid? Well, there are no hard and fast rules here.<\/p>\n

Most are generally rocky, metallic or a mixture of both, but some appear to be icy.<\/p>\n

Some are round, but many are odd-shaped rogues that look like they\u2019ve been involved in some major celestial crashes.<\/p>\n

Most live in the zone between the orbits of Mars and Jupiter in an area that is commonly referred to as the asteroid belt<\/a>.<\/p>\n

However, there are many that travel all over the place \u2013 occasionally hitting anything in the way.<\/p>\n

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An illustration showing a \u2018bird\u2019s eye view\u2019 of our asteroid belt, which lies between the orbits of Mars (red) and Jupiter (purple). Green dots represent asteroids. Earth\u2019s path round the Sun is in blue and red indications comets and asteroids with orbits that pass close to Earth. Credit: NASA\/JPL-Caltech.<\/span><\/figcaption><\/div>\n

While crashing into our planet and causing global devastation, an asteroid led to the extinction of the dinosaurs<\/a>.<\/p>\n

The largest\u00a0 asteroid in the asteroid belt is Ceres, which was the very first one that was discovered.<\/p>\n

Italian astronomer Giuseppe Piazzi at his observatory in Palermo, Sicily, found an object that he named Ceres<\/a> on 1 January 1801. This tiny world is a mere 975km (605 miles) across.<\/p>\n

All the others in the belt are smaller than this.<\/p>\n

Indeed, there are very few asteroids you would class as big: fewer than 20 are larger than 250km (155 miles)<\/span> across, and once we get down to \u2018shards\u2019 of around 1km<\/span> (0.6 miles) to 2km (1.2 miles) in diameter, the total could be well into the high hundreds of millions.<\/span><\/p>\n

Where do asteroids come from?<\/strong><\/h2>\n
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Craters on asteroid Eros, imaged by the NEAR Shoemaker spacecraft from a distance of 35 kilometres above the surface. Credit: NASA\/JPL\/JHUAPLNASA\/JPL\/JHUAPL<\/span><\/figcaption><\/div>\n

Some interesting ideas can be formed about how all these asteroids came into being.<\/p>\n

The fact that their make-up varies from being all rock to all metal, and every stage in between, suggests that some used to be larger objects that went through a process of differentiation before being split apart.<\/p>\n

Differentiation is when big objects with lots of gravity heat up, which causes molten material to move about.<\/p>\n

The metals sink to the centre because they\u2019re heavier and the rocks rise to the surface because they\u2019re less dense.<\/p>\n

When something comes along and smashes it up, you\u2019re left with a variety of mixtures.<\/p>\n

The reason they\u2019re in a belt between Mars and Jupiter could be that there just wasn\u2019t enough stuff to make a planet, or perhaps the massive gravitational tugs of nearby Jupiter just kept breaking apart anything that tried to form.<\/p>\n

How to see an asteroid<\/strong><\/h2>\n
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The comet-like asteroid P\/2010 A2. Credit: NASA, ESA and D. Jewitt (UCLA)<\/span><\/figcaption><\/div>\n

If you\u2019re looking for an asteroid, you ideally need two clear nights in a row, or at least within a few days of each other.<\/span><\/p>\n

This is because these objects appear just like stars or planets \u2013 they don\u2019t move as you watch them.<\/span><\/p>\n

Therefore, you need a second observation to see their shift against the background of normal stars.<\/span><\/p>\n

Finding them to start with is a matter of using a star chart, an astronomy smartphone app or software such as RedShift<\/a> or Starry Night<\/a> that shows you a location chart.<\/span><\/p>\n

Or you can read our observing guide to find out what comets and asteroids are in the sky tonight<\/a>.<\/p>\n

5 of the brightest asteroids visible in the night sky<\/strong><\/h2>\n
1<\/span>

4 VESTA<\/h3>\n<\/div>

\u00a0<\/p>\n

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Asteroid Vesta, as seen by NASA\u2019s Dawn spacecraft. Image credit: NASA\/JPL-Caltech<\/span><\/figcaption><\/div>\n