The International Sun-Earth Explorer-3 was launched on Aug. 12, 1978 to study the solar wind, a stream of highly-charged electrons and protons flowing from the sun toward earth. After fulfilling this mission ISEE-3 had its orbit changed from a geocentric to a heliocentric one in 1985 in order to study the composition of the tail of comet Giacobini-Zinner. In 1997, NASA deactivated ISEE-3 and the spacecraft has been drifting in an orbit about the sun for the past 17 years. Now a group of amateurs and retired space workers, including now-retired project director Dr. Robert Farquhar, are hoping to return the craft to a usable orbit about the sun and then to one about the earth. Ultimately the hope is to place it in the National Air & Space Museum.
The problems are monumental. NASA abandoned the project so long ago the original command manuals have been lost, the project command post scrapped, and scientists involved long-since retired. Still the group made contact with ISEE-3 this past May as it has been transmitting all these years even though the receivers are gone. Whatever happens must be soon, for in a few weeks, the opportunity to use the moon’s gravity to place ISEE-3 back in a heliocentric orbit will be gone along with any hope of recovering the spacecraft.
Focus on the planets
Mercury is too faint to see until mid-month when it makes an appearance in the east-northeast to the lower left of Venus. On July 16 Mercury makes its closest approach to Venus and the two are visible together for the remainder of the month.
Venus rises in the east at the start of morning twilight and, although it is sinking lower on the horizon, is the brightest celestial object in the sky other than the moon. On July 15 Venus dominates the east-northeast horizon before dawn with Mercury to its lower left and Aldebaran to the upper right.
Mars is in the southwest as darkness falls and remains in view until midnight. On July 5, Mars is extremely close to the moon about an hour after sunset with the bright star Spica to the left.
Jupiter makes a very brief appearance above the northwest horizon about an hour after sunset as July opens but sets a half hour later. Jupiter vanishes from sight behind the sun by mid-month.
Saturn is a third of the way up the south-southwestern horizon as twilight gives way to darkness. Saturn is dimming and shrinking in size but its ring system is still spectacular and its largest moon Titan is readily spotted. On July 7 look for Saturn nestled at the top of the moon about an hour after sunset.
Neptune lies above the eastern horizon among the stars of Aquarius at midnight where its blue-gray disk can be found with a good set of binoculars.
Uranus is in Pisces and well up on the southeast horizon as night gives way to morning twilight. Its blue-green disk should be spotted by binoculars. Both of the outermost planets can be found with the aid of the finders charts at the Sky & Telescope website skypub.com/urnep.
July Events
1 Sunrise, 4:53 a.m.; sunset, 8:25 p.m. Regulus is to the upper right of the crescent moon tonight.
4 The earth is at aphelion or farthest distance from the sun. Oddly enough, perihelion or closest approach to the sun occurred on Jan. 4 this year. Why is it colder when the earth is closer to the sun? Think about it.
5 The moon, Mars, and Spica make an impressive trio in the southwest tonight. First quarter moon, 7:59 a.m.
7 Look for Saturn nestled just above the moon tonight with red Antares far to the lower left.
12 Full moon, 7:25 a.m. The full moon of July is known as the Hay Moon, Thunder Moon, or Buck Moon.
13 The moon is at perigee or closest approach to Earth. Coming as it does right on the heels of the full moon, above average high tides may occur.
18 Last quarter moon, 10:08 p.m.
21 The sun enters Cancer on the ecliptic.
22 Aldebaran, the “Red Eye” of Taurus the Bull, lies close to the lower right of the moon at dawn. The sun enters the astrological sign of Leo even though, astronomically, it has just entered Cancer.
24 Venus stands to the immediate left of the crescent moon about an hour before sunrise with Mercury to the pair’s lower left.
26 New moon, 6:42 p.m.
28 Moon at apogee or farthest distance from earth. Even though the moon goes through apogee every month it is reported that this will our satellite’s most distant point for the year.
30 This is the peak night for the Southern Delta Aquarid meteor shower. The peak radiant will occur an hour or two before dawn and will yield a density of 15-20 meteors per hour. The lone star below the radiant is Fomalhaut. Sunrise, 5:19 a.m.; sunset, 8:03 p.m.