by Kim Malville
Venus is low in the southwest throughout September and deserves watching, getting into various encounters with Spica, the Moon, and Saturn.
September 5/6: Look for first magnitude star Spica twinkling madly below Venus
September 8: Venus and the moon will get really close. As viewed from Brazil, Argentina, Uruguay, and Chile, the moon will occult Venus.
September 17/18: Venus moves close to Saturn.
September 22: Autumnal equinox will occur at 2:44pm when the sun crosses the celestial equator heading south.
The Perseids were good this year
As predicted, comet dust rained down last month on planet Earth in the annual Perseid meteor shower. There have been many wonderful photographs of this year’s meteor shower, but the best is by Chinese astronomer Xiang Zhan who made a series of 10 second long exposures over a period of four hours on the night of August 12/13. Combining frames of 68 meteors, he produced a this remarkable composite. Although the sand-sized comet particles are traveling parallel to each other, the resulting meteors appear to radiate from a single point on the sky in the constellation of Perseus. This illusion is the same as that of parallel railroad track, which appear to converge at a distance. If you look closely at the photo, you can see the “wish-bone” shape of Perseus. Above the radiant out of which the meteors come is the brilliant double cluster of new stars, which easily visible in the dark skies of Crestone.
For a high school project many years ago, I spent several weeks on the slopes of Mt Tamalpais overlooking San Francisco, counting Perseid meteors. Later, I was involved in a program in the Antarctic searching for bursts of faint telescopic meteors, which had once been reported at Little America. I continued to be awed by the silence and sudden brilliance of these meteors appearing without warning in the sky overhead. The brighter Perseids leave a luminous trail in their wake, making them even more memorable. These tiny fragments of dust were produced during the birth of the solar system over four billion years ago and have been gathered together in the icy embrace of comet Swift-Tuttle. All meteor showers result from comet debris, but Swift-Tuttle is one of those comets, with a diameter of 16 miles. As a result, the Swift-Tuttle tail contains many particles that are large enough to produce fireballs. Over the past six years, observers have reported about 100 fireballs (a few as brilliant as Venus) per year, more than seen in any other shower.
The Sun’s magnetic field is about to flip
Within the next few months the magnetic field of the sun is going to make a 180° turn. It’s a flip that occurs every 11 years as the sun reaches the peak of its solar cycle. The sun’s north pole has already changed sign, while the south pole is racing to catch up. Right now it is a very odd magnetic system with two positive magnetic poles.
Normally the sun is a huge N-S magnet, like our Earth. In addition it has small pockets of intense magnetic fields which make their appearance as sunspots. Our Earth’s field has small anomalies, produced by pockets of iron ore, but they are nothing compared to power of sunspots. Fortunately, the Earth’s field does not flip as frequently as the sun. The last time we flipped was about was 780,000 years ago. While a flip of the Earth’s field is a serious event since it leaves us briefly without a magnetic field to protect us from incoming charged particles (except for the protective layer of the atmosphere) there should be no great consequences for us on Earth for the sun’s flip. No need to rush out for purchase protective head gear.
Huge lava fountains are gushing from Jupiter’s moon
One of the most massive volcanic eruptions in the solar system was recently spotted on Jupiter’s moon Io, by a telescope perched, no less, on top of a volcano on Earth.
On 15 August the Keck II telescope on Mauna Kea in Hawaii recorded fountains of lava gushing from fissures in the Rarog Patera region of Io. Heated by gravitational squeezing from Jupiter and its other moons, Io is covered in volcanoes that erupt almost continuously. This particular event is easily one of the 10 largest volcanic explosions yet seen on Io by humans. The lava fountains spouted molten rock 1000 feet above Io’s surface, erupting over an area totaling 31 square kilometres. The Galileo spacecraft, which visited Jupiter from 1995 to 2003, was the last mission to get a close up view of the action on Io. Since then, monitoring of Io by Earth-based telescopes have shown how much violence a squeezed moon can produce. The biggest eruption seen so far happened in 2001, when the Keck observatory saw a lava flow that spread many hundreds of square kilometres across Io’s surface. In 2007 the New Horizons spacecraft spotted huge plumes from a volcano called Tvashtar as it flew past Io on its way to Pluto. A rocky body roughly the size of our moon, Io has relatively low gravity and almost no atmosphere, which is why its volcanic eruptions can spray molten debris much higher than those we see today on Earth. The blasts are also much more intense: an individual eruption can produce 5 terawatts of energy. The total power produced by humans on the Earth these days is about 15 terawatts. Io gives us a view of the massive volcanism that dominated the early years of Earth. It is a wonderful volcanic laboratory, although I doubt that there are many volcanologists who would care to do field work there. In addition to all the bubbling hot pots and exploding volcanoes, Io is deeply immersed in the Van Allen belts of Jupiter. High energy particles are constantly raining down on the surface of this very, very alien world.