The moon dances with ice giants this week, Venus visits a stunning star cluster, and a space mountain offers its best views for 2015.
Neptune visit. Early risers on Tuesday, June 9, can use Earth’s moon as a guide to the farthest giant planet in the solar system.
Neptune is usually a tricky object to identify since, at 7.9 magnitude, it's only visible through binoculars and telescopes. However, the moon makes for a convenient guidepost this morning to the faint blue-green disk hidden among the stars of the constellation Aquarius, the water bearer.
Before local dawn, look for the last quarter moon in the southeast. Icy Neptune will appear less than 5 degrees to the west—about equal to the width of your three middle fingers held at arm’s length.
Three days later, on Friday, June 12, Neptune will come to a full stop in its eastward motion. Known as its stationary point, this represents the time when Earth, in its speedier orbit around the sun, catches up with the distant planet. Until the next stationary point, in November, the gas giant will appear to move westward, or in retrograde motion, in front of the field of stars.
Jovian shadows. Sky-watchers in the western part of North America on Wednesday, June 10, will get a chance to see two of Jupiter’s largest moons eclipse each other.
That evening, the shadows of Ganymede, the largest moon in the entire solar system, and its neighbour Io will appear painted on Jupiter’s disk. At 9:55 p.m. PDT, Ganymede will begin to slip in front of Io, merging the moons’ shadows. Twenty-three minutes later, their black dot-like silhouettes will again separate.
Uranus conjunction. Before dawn on Thursday, June 11, look for the waning crescent moon hanging low in the southeast to help find the tiny greenish disk of Uranus. Shining at magnitude 5.9, the planet should be easy to observe with nothing more than binoculars, even from light-polluted cities.
The two objects will appear to be about 5 to 7 degrees apart—less than the width of your fist held at arm’s length. Their proximity is just an illusion, though, since the moon is 1.2 light-seconds away and the ice giant is 170 light-minutes distant from Earth.
Pallas opposition. One of the largest asteroids in the solar system, 2 Pallas, will be at its brightest in our evening skies on Thursday, June 11, when it reaches official opposition, the point at which it sits directly opposite the sun.
Over the next couple of weeks, the 338-mile-wide Pallas, shining at 9th magnitude, will be an easy binocular target, even from light-polluted city suburbs.
Pallas is currently gliding across the bright constellation Hercules, the strongman, located up the southeastern evening sky, off to the far right (about 19 degrees) of the bright star Vega.
To help in the hunt for this space mountain, first zero in on the faint naked-eye star Lambda Herculis and look about 0.7 degrees (a little more than the width of the full moon disk) below it for the asteroid.
Because many of the stars in the field of view through binoculars can look the same, the best way to identify an asteroid is by its motion. Sketch the position of about a dozen stars in the area of the asteroid. A couple of nights later, observe the same star field again and make the same sketch. The “star” that has moved will be Pallas.
Venus and the Beehive. After nightfall on Saturday, June 13, look for Venus in the west paired up with the pretty Beehive star cluster, also known as Messier 44.
About an hour after sunset, the brilliant planet will be only 1 degree north of the Beehive in the constellation Cancer, the crab. Both objects will appear stunningly super-close in binoculars and should fit into one field of view of a telescope using low power.
While Venus is a mere 5.6 light-minutes away, the Beehive sits some 570 light-years from Earth. The open star cluster contains at least a couple hundred stars that stretch about 24 light-years out in space, making it a favorite of backyards stargazers everywhere.