Astro Payyanur

This week's sky

Early April is the best time for viewing another favorite saturnian moon, Iapetus. This two-faced moon has one hemisphere as bright as snow and one as dark as charcoal. The bright side faces Earth when Iapetus lies far west of Saturn, and the dark side points toward Earth when the moon appears far east of the planet. The upshot: Iapetus' brightness changes by a factor of five as it orbits Saturn. The moon shines at its brightest when it reaches greatest western elongation April 2. It then glows at magnitude 10.1.

No other planet rises until well past midnight. The first to appear is Jupiter, which leads the pack of three other planets -- Neptune, Venus, and Mars -- congregating in the morning sky. At magnitude -2.1, Jupiter shines far brighter than any other object in the dim region of sky inhabited by Capricornus. It rises by 5 a.m. local daylight time April 1.

This week's sky



Meteor activity remains low during March. The only shower is a minor one deep in the southern sky. Still, you might see fine meteor dust in the form of the zodiacal light. This faint glow shows up best from dark observing sites during the moonless evenings after mid-March. Well after the Sun sets, twilight's last gleaming will give way to a lingering cone-shaped glow - the zodiacal light. The glow extends up through Aries and into Taurus.

The zodiacal light represents sunlight reflecting off dust particles concentrated along the ecliptic, the plane of our solar system. Because the dust lies in the ecliptic plane, the glow follows the constellations of the zodiac (hence the name). The glow shows up best when the ecliptic makes a steep angle to the horizon. In the Northern Hemisphere, this happens on evenings in early spring.

If you have a telescope, mark April 2–5, 2009, on your calendar. The world is coming your way.

An unprecedented string of public skywatching events will be packed into this brief period, all designed to engage people and bring them out for a worldwide star party that will cap the program on Saturday evening, April 4th.

Collectively, the period is called “100 Hours of Astronomy.” It’s a Cornerstone Project of the International Year of Astronomy 2009, tailor-made for amateurs who’d like to try some outreach. During the final 24 hours a global star party will sweep around the world, with local gatherings beginning as darkness descends. Even city street corners will come alive, with the third annual International Sidewalk Astronomy Night happening the first weekend in April. Thus many sidewalk astronomy regulars will already be at their stations.