Night Watch

Imagine yourself sitting on a rock on the dark side of Moon, gazing up at the Milky Way. There's no stray lights, no atmosphere to dull your view of the night sky. The stars are so brilliant, so big, you could reach out and touch them.

We can't take you to the dark side of the Moon just yet, so find yourself a nice dark area of the garden. You can see some of the brightest stars in the sky during these cold August nights.

One of those brilliant stars is Vega. You can find it low in the northern sky during these cold August nights.

About 25 years ago, astronomers found that a broad disk of warm dust grains surrounds Vega. But the disk has big lumps and gaps. These may be caused by the gravity of planets orbiting the star, which sweep away the dust in some areas of the cloud, and cause it to clump together in others.

The clumps may be caused by a planet about as massive as Neptune, one of the giants of our own solar system. But there's evidence of smaller planets, too, orbiting much closer to the star.

None of these planets, if they exist, is a likely home for life. Vega's only about 350 million years old; less than one-tenth the age of the Sun, so there probably hasn't been enough time for life to evolve there. And even if life did form, Vega's much hotter than the Sun, which makes it an unfriendly environment.

But since late 1995, astronomers have discovered over 200 possible planets in other star systems. These stars all look rock-steady. But sensitive instruments reveal that the stars "wiggle"; and that's how astronomers discovered most of their planets.

Astronomers have found most of the planets by measuring a tiny "shift" in the light from their stars. The gravity of an orbiting planet pulls at a star, causing it to move a bit, which creates a shift in the wavelengths of the star's light. Most of the planets are giants; from roughly a quarter the mass of Jupiter, up to perhaps a dozen times more massive.

Almost none of the planets are considered likely homes for life. Many are so close to their parent stars that they're quite hot. And since the planets are so massive, they're probably balls of gas with no solid surfaces; just like Jupiter.

As time goes on, though, astronomers expect to start finding planets that are similar to Earth. Small, rocky worlds at comfortable distances from their stars: planets that just might harbour life.

And it's on one of Jupiter's moons that we might find life in our solar system (other than the Earth). One of Jupiter's most fascinating moons is Europa. It's coated by ice, which may float atop an ocean of liquid water.

Water is one of the essential ingredients for life, so where there's water, there's a chance we'll find living things. But diving into this ocean won't be easy. Europa has no atmosphere to speak of, and its surface temperature is about 280 degrees below zero °C. And the icy crust is probably kilometres thick in most places, so we'll have to find a spot where it's thin enough to drill through.

If humans ever dive on Europa, they'll need extra-thick wetsuits to protect them. They'll also need strong lights, because the ice keeps out sunlight. No one is sure if divers will find life in Europa's ocean. It may be too cold and slushy to sustain life. On the other hand, the water may be warmed by volcanic vents, like those found on the ocean floor.

If you want to see Jupiter for yourself, it will be hard to miss. It dominates the eastern evening sky. Other than the Moon, it's the brightest object in the evening sky.

Astronauts, looking out of the space shuttle windows at night, see great clusters of lights; the glow of hundreds of thousands of individual lights that mark cities on earth. From the ground, we can see great clusters of lights in the heavens, too; cities of stars we call globular clusters. They're somewhat lost in the background of stars, but binoculars or telescopes reveal their true nature: spherical clumps of thousands or even millions of stars. Our Milky Way galaxy contains a couple of hundred globulars.

An image of Omega Centauri from Stockport Observatory by Tony Virgo
(more images by Tony Virgo)

Omega Centauri orbits the centre of our Milky Way Galaxy, like the Sun does, but its orbit carries it far outside the Galaxy's flat disk. It occasionally dips through the disk - an event that strips most of the gas and dust from the cluster and prevents new star formation.

Omega Centauri may have formed when two clusters rammed into each other billions of years ago. The collision may have given the cluster two sets of stars, one of which is several billion years younger than the other.

You can see Omega Centauri with the naked eye, as a small fuzzy patch in the southwestern sky. It's visible to the unaided eye, but only binoculars or a telescope reveal its full glory; a dazzling city of stars.

The Moon is Full on August 6th, at Last Quarter on the 14th, New on the 20th, and at First Quarter on August 27th.