August 2001 Sky from Keeble Observatory

Seventy percent of Earth's surface is covered with water. The oceans give the planet its distinct blue color when seen from space. And, water is essential to life as we know it. About 70% of your body weight is water. That blood plasma is almost identical to sea water in its percentages of dissolved salts and other minerals is powerful testimony to the probable origins of life in Earth's ancient tidal pools. Earth's distance from the Sun allows water in all three of it physical phases - solid, liquid, and vapor - and we often see all three coexisting simultaneously.

Water is also ubiquitous in interstellar space, where we can detect this molecule by observing with radio and infrared telescopes. Water ice is a major component of comets in our own solar system, and it makes up a major component of the frozen moons of the outer planets. The Galileo probe orbiting Jupiter has provided tantalizing evidence that there may be liquid water beneath the icy moons' surfaces. There's even evidence for water ice in deep, perpetually shadowed craters near the poles of the Moon and Mercury. Our best models suggest that the widespread presence of water in the Solar System reflects the overwhelming abundance of hydrogen in the universe, and the fact that oxygen is the third most abundant element in our neighborhood of space. (The proportions are daunting - there is roughly one oxygen atom for every thousand hydrogen atoms.) Nitrogen and carbon, two elements also essential for life as we know it, are even less plentiful.

We've known of extra-solar planets, i.e. worlds orbiting other stars, from the wobble they induce in the motions of those stars. But, we've not had any means to analyze those worlds to determine their composition. Their similarities or differences when compared with the planets and comets around the Sun would help us to test the correctness of our models. We now have evidence that water has been incorporated into comets and possibly planets beyond our solar system. Observations made with the Submillimeter Wave Astronomy Satellite (SWAS) have detected abundant water vapor surrounding a star where we wouldn't expect water from the star itself. The star in question is CW Leonis, an older, carbon-rich star about 500 light years away in the constellation Leo. The star is in its red giant phase, late in its evolutionary cycle. Because the star has more carbon than oxygen, most of the oxygen in its expanding stellar wind should be bound into carbon monoxide, and there should be almost no water showing in its spectrum. Yet, we are seeing a lot of water. The mass inferred for the water suggests that the star is simultaneously vaporizing its entire cohort of perhaps hundreds of billions of comets. This is happening because the red giant is far more luminous than the star was when still on the main sequence and much more like our own Sun at present. Thus, it is heating the comets even at distances where they have remained in a deep freeze since the star formed some 10 billion years ago.

Lunar phases for August: Full Moon on the 4th, at 1:56 am; Last Quarter on the 12th, at 3:33 am; New Moon on the 18th, at 10:55 pm, First Quarter on the 25th, at 3:55 pm.

Evening planet watchers will have to content themselves with Mars, which is still visible to the south, though fainter than it was at opposition in May. Mercury will be visible to the west at dusk later in the month. Venus will dominate the planetary view just before dawn, but will have company as we catch up to Jupiter. Early in the month, Jupiter will be about 1.5 degrees above and to the left of Venus, later in the month it will be above and to the right, widening their separation to about 25 degrees by month's end. Saturn is also visible, about 25 degrees above and to the right of Jupiter. By the end of the month, a small telescope will give a spectacular view of the rings, which will be tipped about 26 degrees to the line of sight. The angle of sunlight will cast an impressive shadow on the rings.

Looking overhead at about 10:00 pm at mid-month, we see the bright star Vega at zenith. With binoculars, you will notice that one of the nearby stars in Lyra appears split into a binary. With a small telescope, you will see that this binary is actually two binaries, the so called "double-double." On an exceptionally clear and dark night, you may also notice the pale circle of the Ring Nebula, the remains of an aged star which has ejected its outer layers as an expanding shell of glowing gas. Cygnus is just to the east of Lyra, with bright Deneb towards the left, the fainter but beautiful binary Albireo to the right. Follow the line of the Swan's tail to the northeast to find the familiar tilted W of Cassiopeia, with the lower leg of the letter shape parallel to the horizon. Follow that line to your right and you may see the Andromeda Galaxy if the sky is clear enough. This galaxy, about two million light years distant, is the furthest object directly observable without a telescope. To the northwest lies the familiar bowl and handle shape of Ursa Major. Follow the line from the two stars at the end of the bowl to find Polaris, almost due north. Following the curve of the handle stars back towards the west and you'll encounter bright Arcturus in the constellation Bootes. To the south, we still see Scorpio. Don't confuse Antares with Mars - Mars is the brighter of the two "stars" this month.