This is the Dudley Observatory Skywatch Line for Monday and Tuesday, July 9th and 10th written by Joe Slomka.
The Sun sets at 8:35 PM; night falls at 10:46. Dawn breaks at 3:15 AM and ends with the Sun rising at 5:26.
Bright planets shine in this evening’s twilight. In the West, Mercury, in Cancer, glows with 0.4 magnitude, appears about 8 arc-seconds in size, and looks about half lit. Its low, 8º altitude, means that it sets quickly at 9:57 PM. Mercury is in its descending mode, which means that it gets lower on the horizon daily. Venus, which lies about 16º to Mercury’s upper left, blazes with minus 4th magnitude and appears about 2/3 illuminated. Binocular and telescopic observers will note that Venus snuggles up 1º to Regulus, the brightest star in Leo. At Civil Dusk, Venus is about 17º high; it sets at 10:46.
The Eastern horizon has its own share of bright planets. Jupiter, in Libra, is found due South at Civil Dusk. It blazes with minus 2nd magnitude is a large 40 arc-seconds in size and about 32º high. It is highest at 8:28 PM. Binocular observers will see Jupiter still close to Libra’s brightest star, Zubenelgenubi. Tuesday, telescopic observers can witness the Jovian moon Ganymede begin to cross the planet’s face at 12:13 AM. Later Tuesday, they will see the Great Red Spot (a giant storm) at 10:13 PM. Jupiter sets at 1:34 AM.
Twilight also reveals Saturn, in Sagittarius; it shines with zero magnitude an is about 22º high in the southeast. Saturn is quite low and presents a challenge for astronomers to see details of its marvelous ring system. Saturn is highest at about Midnight and sets at 4:37 AM. At about 10º to Saturn’s upper right lies the asteroid 4Vesta, in Ophiuchus. It still shines with 5th magnitude and is about 25º high during twilight. Those seeking to find Vesta should utilize detailed sky charts from astronomical media. It sets at 3:57.
Mars, 33º to Saturn’s lower left, rises at 10:04 PM, shines with minus 2nd magnitude, is 22 arc-seconds in size and 98% lit. Mars continues to become brighter and larger, in preparation for its July 27th Opposition. This is normally prime time for people to study Martian geography; however, the global Martian dust storm remains unabated, enabling planetary scientists to track weather on a close planet. Mars is best observed at 2:31 AM.
Neptune rises in Aquarius at 11:15 PM and is best viewed at 4:53 AM. Uranus, in Aries, shines with 5th magnitude, is 3.5 arc-seconds in size and is about 25º high by Dawn.
The waning Moon occupies Taurus both days. Tuesday, the 26-day-old Moon rises at 3:06 AM, blazes with minus 5th magnitude and is about 11% lit. Wednesday, it rises at 3:55 AM, gleams with minus 3rd magnitude and is about 5% lit. Wednesday’s Moon is the last easily spotted old Moon.
Vesta was the goddess of the hearth. Roman homes had hearths for cooking and heat; in fact, the hearth was her shrine. Romans said daily prayers to her in thanksgiving for food and heat. The household fire must never go out. Should the fire extinguish, a new fire could only be started from another holy hearth or Vesta’s temple fire. At the temple, six Vestal Virgins, unmarried women, tended to the sacred fire day and night. They enjoyed great esteem and were granted important privileges. Vestalia was a religious festival when the Vestal Virgins would clean the temple and relight the flame with a magnifying glass. Special cakes were baked and offered to Vesta.