This is the Skywatch Line for Monday and Tuesday, July 30th and 31st.
The Sun sets at 8:18 PM; night falls at 10:16. Dawn breaks at 3:48 AM and ends with the Sun rising at 5:46.
The evening sky presents four bright planets. Venus, in Leo, is the brightest at minus 4th magnitude, appears about half lit, and about 14º above the western horizon. It sets at 10:08 PM.
Jupiter, still in Libra, glows with minus 2nd magnitude and stands 27º high in the southern sky. While binoculars will reveal several of the planet’s moons; telescopes allow viewers to witness the moon IO exit the planet’s face at 10:44 PM on Tuesday. Jupiter sets shortly after midnight.
Saturn, still in Sagittarius, is also moderately high in the southern sky, but to Jupiter’s left. Saturn glows with zero magnitude and appears a large 18 arc-seconds in size. Its glorious ring system is best observed at 10:36 PM. Saturn sets at 3:08 AM.
Mars brings up the rear of this evening parade. In Capricorn, the Red Planet reached Opposition last Friday, when it was best aligned for observation. However, Tuesday, it is at its closest approach to Earth at 35,785,000 miles, a distance not equaled since 2003 and will not occur again until 2035. Mars slightly outshines Jupiter and appears 24.3 arc-seconds in size. This close approach presents opportunities for observers; however, the planet-wide dust storm may obscure its surface features. Recently, a European Martian satellite made a potential discovery. Among the satellite’s instruments was a powerful ground-penetrating radar. The scientists revealed that the radar displayed what appears to be a large body of deep underground water. If true, it would be the first stable water observed; some Mars rovers discovered fleeting indications of water. Mars rose after sunset, is best seen at 12:48 AM and sets at 5:04 AM.
Neptune, in Aquarius, rises at 9:51, shines with 7th magnitude and appears a tiny 2.5 arc-seconds in size. However, the nearby waning, 90%lit Moon, only 3 degrees away, rises at 10 PM on Monday and 10:28 PM on Tuesday. Blazing at minus 11th magnitude, its glare will certainly pose challenges for the astronomer. The Moon is best observed at 3:34 AM on Tuesday and 4:17 AM on Wednesday.
Uranus, in Aries, rises at 11:30 PM and shines with 5th magnitude and a larger 3.6 arc-seconds in size. Its distance from the Moon may permit viewing this giant planet. Both Neptune and Uranus require detailed sky charts to assist the observer.
The first artificial satellite, Sputnik, was launched in 1957. A series of military and scientific satellites followed. However, long before Sputnik, Arthur C. Clarke, a novelist, screenwriter and physicist, had a dream. In 1947, he published a paper predicting that a satellite placed in a special orbit could act as a relay for radio signals. Clarke predicted that, if you launched a satellite to orbit high above the Earth at the same speed as the Earth’s, the satellite would appear to be stationary in the heavens. In May 1960, NASA first launched Echo, a silvered Mylar balloon, which literally bounced signals across the Atlantic. On July 10, 1962, AT&T launched Telstar, a true relay station. Telstar received and retransmitted signals between the US and Europe. Today, many such satellites crowd our skies and make worldwide television, telephone and Internet communications routine. Telstar also paved the way for commercial services like Dish TV and satellite radio.