If you haven't yet seen the great planetary gathering that's unfolding in the west at dusk, the first half of May brings your best opportunity. All five naked-eye planets -- Mercury, Venus, Mars, Jupiter, and Saturn -- are well placed for viewing in the western twilight sky about an hour after sunset.
Start by looking high in the west for bright Jupiter; you can't miss it. Next find brilliant Venus down to Jupiter's lower right. The other three planets are much fainter (especially little Mars) and are gathered in Venus's general vicinity.
"If there's one date not to miss, it's May 14th," advises Alan MacRobert, a senior editor at SKY & TELESCOPE magazine. "That's when the crescent Moon is closely paired with brilliant Venus. Just look west in twilight -- it'll be a dramatic sight. The other planets will emerge as darkness grows deeper."
The finale of this season's planetary convergence comes on June 3rd: a close conjunction (pairing) of brilliant Venus and Jupiter.
Descriptions of the planetary arrangement each evening for the next few weeks can be found on SKY & TELESCOPE's Web site: http://SkyandTelescope.com/observing/objects/planets/article_572_1.asp
Close gatherings of the five naked-eye planets are relatively rare. Every 20 years, we get a period a few years long within which these worlds can all gather in more or less the same part of the sky as seen from Earth's perspective. The last widely visible five-planet bunching was in February 1940. (A tight grouping occurred in May 2000 but was hidden in the Sun's glare.) Another good one won't take place until September 2040. So for many of us, this year's display represents a once-in-a-lifetime opportunity.
The twilight gathering of planets above the western skyline provides a fine "photo op" for anyone wanting a memento of the occasion. According to Dennis di Cicco, a veteran astrophotographer and senior editor at SKY & TELESCOPE magazine, "Today's popular point-and-shoot cameras, including the new generation of digital cameras, can easily capture this celestial spectacle." Simply place your camera on a firm support such as a tripod or a windowsill, disable the flash, frame the scene in the viewfinder, and open the shutter for a few seconds. If your camera offers manual overrides, set the focus for infinity and the lens to its maximum aperture (lowest f/number). Because twilight changes rapidly, take a set of "bracketed" exposures lasting about 1, 2, 4, and 8 seconds each. At least one of them is likely to come out well.
Having a tree or building silhouetted in the foreground will make the picture's composition more interesting, di Cicco suggests -- and it will help during the processing of your film, since the planets create such small specks on the negative that the frame may look blank and not be printed.
Stargazers worldwide can use SKY & TELESCOPE's Interactive Sky Chart to simulate the planetary parade as seen from their particular location: http://SkyandTelescope.com/observing/skychart/