Perhaps it was a fleeting glimpse of a shooting star burning up in the Earth's atmosphere that caught your imagination, the curiously blotched face of the man-in-the-moon or the brilliance of the planet Venus. Or maybe it was simply the scale of it all, the vast sheets of stars that puncture the inky darkness of space and the knowledge that you are staring infinity in the eye.
If you have the eyesight, the heavens might reveal the horizon-to-horizon smear of stars that is the Milky Way, the devilish glint of a red giant star like Aldebaran, the eye of the constellation Taurus, or the nightly meandering of the planets Mars, Jupiter and Saturn. The luckiest stargazer may even have seen the haunting image of a passing comet like Hale Bopp or even a total eclipse injecting a shock of darkness to the middle of the day. Countless generations have shared the awe that the night sky can provoke. We may never know what the prehistoric ancients thought they saw - perhaps the distant camp fires of some celestial realm.
The changing heavens helped mark the passing of the seasons and some believe the great stone circles erected thousands of years ago recorded and read the stellar calendar. The first civilisations set great mythical figures striding through the constellations and pondered the influence on our terrestrial lives that the mysterious movements of the stars, planets, Sun and Moon might have. Newspaper astrologers still worry about this.
Once we thought the cosmos had the Earth fixed at its centre, with the stars whirling around us. Now we know th streaks of light left by the passage of the stars in our picture are the result of the spinning of our own planet amid the apparently static enormity of the universe. Old superstitions have crumbled, systematically swept away by a scientific revolution driven by enquiring minds and empowered by innovations like the telescope.
Today, thanks to a dizzying array of astronomical instruments, from the Hubble Space Telescope to Jodrell Bank, we can explore the cosmos in astonishing detail. Every last bit of information is squeezed from the light and other signals that reach us from beyond. Once impossible questions give way to human ingenuity, yet all the time new wonders emerge. We find our Sun is just one of 200 billion stars in the Milky Way, itself lost among an equally vast throng of galaxies. We can look back in time and space to goggle at the fire ball that followed the Big Bang, witness the grisly destruction wrought by black holes, and be present at the birth of new stars in vast dusty stellar nurseries.
Meanwhile, new planets have been detected orbiting nearby stars, raising the prospect that life exists beyond the Earth. Some argue that the ever more sophisticated explanations devised by scientists rob the heavens of their mystery. Not so. Take another look into the night sky. Despite our knowledge, we have more questions to ask of it than ever. And it is still breathtakingly beautiful. Picture by: Joe McNally
* Web links
Hubble Space Telescope: http:hubble.stsci.edu
The night sky: www.jb.man.ac.ukpublicnightsky.html
The search for extraterrestrial intelligence: www.seti-inst.edu
Steve Farrar is science reporter of The Times Higher Education Supplement