Skywatch Line for Monday and Tuesday, June 25th and 26th, 2018

This is the Skywatch Line for Monday and Tuesday, June 25th and 26th.

The Sun sets at 8:38 PM; night falls at 10:54. Dawn breaks at 3:01 AM and ends with the Sun rising at 5:18. Since Thursday’s Solstice, we have already lost one minute of daylight.

Three bright planets inhabit the southwestern evening. Venus, in Cancer, is the brightest, blazing with minus 4th magnitude and appearing about 72% illuminated in binoculars or telescope. It sets at 11:02 PM. It still lies near the Beehive star cluster. Mercury, in Gemini, 13º to Venus’ lower right and 8º high, shines with minus 0.3 magnitude and appears about 70% lit. It sets at 10:03 PM.

Jupiter, in Libra, glares with minus 2nd magnitude about 32º above the southwestern horizon. It appears a large 42 arc-seconds in size, still close to the star Zubenelgenubi. Telescopic observers might see the Great Red Spot (a giant storm) at 9:01 PM on Monday. Also, on Monday, they can see Jupiter’s moon Ganymede finish crossing the planet’s face at 10:43. Jupiter is highest at 9:25 PM and sets at 2:30 AM.

The eastern evening sky has its own attractions. The Moon rose earlier and, by civil twilight, lies in Ophiuchus, blazing with minus 11th magnitude, appearing about 95% lit and about 22º high in the East. Tuesday’s Moon is a bit brighter and more illuminated. It is best observed at 11:21 PM on Monday and at 12:09 AM on Tuesday. It sets at 4:19 AM on Tuesday and at 4:59 AM on Wednesday.

Saturn, in Sagittarius, is about 9º to the Moon’s lower left. Shining at zero magnitude and appearing 18 arc-seconds in size, it hovers about 18º above the eastern horizon. Saturn is best observed at 1:04 AM and sets at 5:37. Asteroid 4Vesta lies about 4º above Saturn. It shines with 5th magnitude and appears about 0.6 arc-seconds in size and 23º high. One week after its Opposition, Vesta should still be naked-eye visible from dark rural areas; detailed sky charts from astronomical media help finding it. It rose at 7:44 PM, is best observed at 12:27 AM and sets at 5:09 AM.

Mars, in Capricornus, rises at 10:56 PM and is best observed at about 3:30 AM. It gleams with minus 2nd magnitude and appears about 20 arc-seconds in size. It continues to become brighter and larger in our telescopes. The dust storm, reported last week, has now spread to half the planet. While it may hide surface features, the storm itself is worth watching because we are witnessing weather on another planet.

Neptune rises near the star Phi Aquarii at 12:10 AM; it shines with 8th magnitude and, by Dawn, is 26º above the horizon. Uranus, in Aries, rises at 1:50 AM, shines with 6th magnitude and appears about 12º high at Dawn.

Last week, the asteroid 4Vesta appeared close to the Beehive open star cluster, also known as M 44. The word “Beehive” is actually a nickname. The formal name is Praesepe, which is Latin for “manger.” Greek legends call Cancer’s stars Delta and Gamma the northern and southern donkeys; inspiring a manger to feed them.

This star cluster is bright enough for naked-eye viewing. In 250 BC, Aratus of Soli called it “little mist.” Hipparchus, in 120 BC, described it as “little cloud.” In 1610, Galileo turned his newly built telescope toward it and declared it a “mass of over 40 small stars” and even sketched the formation. Binoculars show it as a star cluster; the smallest telescopes reveal between 50 and 100 stars. A dozen stars shine at 7th magnitude or brighter. Observation reveals that massive stars are clumped towards the center, while lighter stars form the edges. Studies show that M 44 shares a common motion with the Hyades, and maybe shared a common origin. Two Jupiter-sized planets were discovered among the outlying stars; these are the first “hot Jupiters” found in an open star cluster.

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