It's the beginning of an annual astronomical event called the Perseid meteor shower, often known to astronomers just as "the Perseids", so it's just the right time to introduce you to the app for meteor watchers called "Fireballs in the Sky".
What does this project do?
It is building up a database of the bright meteors and fireballs people see, including the directions from which these objects appear to come. This information tells us where in the Solar System these pieces of matter originated, which again tells us more about the Solar System itself.
What do I have to do?
Go to the website, or get the app "Fireballs in the Sky" on the app or google play stores. Then be patient ...
If you are looking up and see a bright dot or streak of light crossing the sky, too fast and erratically to be an aeroplane or satellite, this may be a fireball. Note that you can sometimes see the especially bright ones by day. Listen hard to see if you hear a sound; the very loudest make a sonic boom, which sounds like thunder.
If you see something like this, open the app and tap "Report a Sighting". You'll first be asked if you heard a sound. After this, point your phone to where the fireball seemed to begin its journey in the sky - it will take care of the constellations and the exact height and direction for you. Tap the circle in your screen when it is at the right place, and then repeat the process for where the fireball seemed to disappear.
After this, you can adjust parameters such as the brightness, colour and whether it seemed to be breaking up into fragments.
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Fireballs in the Sky is part of the Desert Fireball Network, an array of cameras across Australia. These cameras take automatic 30-second exposures, which is enough to show a meteor's presence and direction. Although it originated in Australia, citizen scientists from all over the world use the Fireballs in the Sky app. Sightings from different places, which show the same meteor from different angles, help scientists pinpoint exactly where one of these space rocks is coming from - and in places such as the Australian desert, make it easier to find them.
A fireball is a meteor - a particularly bright one, of magnitude -4 or brighter, about the same as the planet Venus. (In astronomy, the lower the magnitude, the brighter the object is.) This might mean that it was seen close up, or that it was a particularly large object. Most meteors are only about the size of a grain of sand, but a few of course are much bigger - the one that killed the dinosaurs would have been about 10-15km in diameter! Finding a meteorite is many an astronomy enthusiast's dream (a meteor is what you see in the sky; a meteorite is the solid object that has fallen to the ground) - and these objects, mostly being made of the raw material from which the Solar System grew, tell us a lot about why we're here and how we formed. You can see a list of where meteorites have been found here, and how they've been treated historically here.
The Perseids, the upcoming meteor shower, is so named because the meteors appear to be originating from the constellation Perseus. Obviously, the meteors have nothing to do with Perseus, whose brightest star, Algol, is so far away that it takes light 90 years to travel between it and us. These meteors come from a trail of debris left behind by the comet Swift-Tuttle. (Comets are full of light molecules, like water, which evaporate easily when they come near the Sun. This is why they have their amazing bright "tails".) The comet happened to cross the path of Earth's orbit once upon a time, and every year, the Earth now ploughs through the same cloud of debris left by Swift-Tuttle. When a piece of this debris (a grain of sand, for example) comes into contact with our atmosphere at high speed, it becomes very hot and glows. Incidentally, this heat is not due to friction as is commonly thought, but compression: molecules of air in front of the meteor have no time to move out of its path and are thus squeezed together!
If you are interested in fireball-hunting, the Perseids are a good time to look. They last from mid-July until late August, but peak around 12-13 August. You can find the constellation Perseus in the north-eastern sky. High up you will see a W-shape; this is the constellation Cassiopeia. Closer to the horizon will be Perseus. A park or garden, without too many artificial lights in front of your eyes, is a good place to look, but the fewer lights and the fewer tall objects nearby the better. Earthsky and Sky and Telescope have many tips for successful meteor-watching. However, if you miss it, don't despair - there will be many more meteor showers, and a fireball might appear at any time, even during the day.