At a distance of around 8 billion kilometers (5 billion miles, or 54 AU -- a little beyond Pluto's orbit), an icy space rock silently hurtles toward the inner solar system steadily gaining speed.
This piece of space debris -- composed of primordial rock and ice -- measures no more than 26 kilometers (16 miles) in diameter, and as it plunges sunward, it will pass the orbits of Pluto, Neptune, Uranus, Saturn, Jupiter, Mars and even power through our neighborhood before being flung back into the depths of interplanetary space.
You'd think that's all we would see of Comet Swift-Tuttle until it returns in about 133 years time, but you couldn't be more wrong.
Every year we are reminded of its fleeting presence as the Earth intercepts the comet's orbit and sweeps up some of the fragments it left behind. Like a celestial vacuum cleaner, Earth collects everything in its path and treats us to one of the greatest shows the Universe has to offer: the Perseid meteor shower.
Through the year, there are around 30 decent meteor showers and the Perseids are some of the finest meteor examples around mid-August every year.
As the countless pieces of dust slam into our atmosphere at over 100,000 kilometers per hour (17 miles per second!), they compress the air to such a degree that the gas heats up, generating light. We see this as the characteristic shooting star effect. The smaller pieces of dust will burn up high in the atmosphere and we call them "meteors." (Larger pieces of debris that survive the fiery plunge and hit the ground are called "meteorites" -- but these are rare and it is highly unlikely any Perseid will fall into this category.)
It's possible to see meteors any time of year, we call them "sporadic" and they are not associated with any shower. If you study the meteors from a particular shower though, you will see that they all come from one point in the sky. This point is known as the "radiant" and it's the location of the radiant that determines the name of the shower. In the case of the Perseids, the radiant lies in the constellation Perseus.
The Earth has already started to enter the fragments -- or "meteoroids" -- from the Swift-Tuttle stream, and Perseid meteors can be seen in our skies right now. Activity is picking up so it's worth going outside over the next few nights to see how many you can spot.
The peak of activity is predicted to be in the early hours of Saturday (Aug. 13), but unfortunately the light of the full moon will block many of the fainter meteors.
The best time to catch the Perseids is in the early hours after midnight when you will be on the "forward" facing side of the Earth's orbit. So, wrap up warm, find a dark spot away from lights, lie back on a comfy chair and gaze skyward.
As I found out while presenting the BBC's Stargazing LIVE, it's very easy to be looking in the wrong direction! But keep alert and you will hopefully get to witness what is, in my opinion, one of the greatest wonders of the Universe.
© 2012 Discovery Channel