With some diligence, you might be able to catch all five visible planets in July 2011. By visible planet, we mean any planet that can be viewed without an optical aid and that was known to our ancestors since time immemorial. In their outward order from the sun, the visible planets are Mercury, Venus, Mars, Jupiter, and Saturn.
Evening planets: Mercury and Saturn
Two visible planets adorn the evening sky throughout July 2011: Mercury and Saturn. Mercury is the solar system’s innermost planet and Saturn is the most distant world that you can easily see with the unaided eye. Whereas Saturn remains an evening object until October 2011, Mercury swings from the evening sky to the morning sky in August 2011.
An imaginary line from the planet Saturn through the star Regulus points close to the planet Mercury in July 2011
For the northern hemisphere, July 2011 presents Mercury’s best appartition as an evening “star” for the rest of this year. Even so, you’ll need a level and unobtructed horizon to catch Mercury low in the west-northwest sky some 45 to 60 minutes after sunset. (For reference, the sun sets in the west-northwest at this time of year.) Although Mercury shines as brightly as a first-magnitude star, its luster is somewhat tarnished by the twilight glare. If you can’t see this world with the unaided eye, try binoculars. At mid-northern latitudes, Mercury sets about 75 minutes after the sun.
Saturn is the easier of the two evening planets to catch. It pops out into the southwest sky at dusk, and stays out until late night. Now, and for the rest of 2011, Saturn resides in front of the constellation Virgo, fairly close to Virgo’s brightest star Spica. You can distinguish Saturn from Spica by color. Saturn exhibits a golden hue, whereas Spica sparkles blue-white. Although Saturn is easily visible to the unaided eye, you’ll need a telescope to see its glorious riings. Look for the moon close to Spica and Saturn on the evenings of July 7 and 8.
Look for the moon between the red planet Mars and the Pleiades star cluster before dawn on Tuesday, July 26.
You’ll have to stay up late or wake up early to see the morning planets. Jupiter rises first around midnight, followed by Mars and then Venus. Venus, the sky’s brightest planet, nonetheless will be difficult, if not impossible, to see because this world rises a very short while before sunrise and sits in the harsh glare of twilight. Venus passes into the evening sky on August 16, which is nearly the same date that Mercury swings into the morning sky.