Under dark, moonless skies this week, the king of the celestial jungle revels galactic treasures, and Saturn points the way to the Scorpion’s stellar claw.
Target Neptune. With a little help, early risers on Tuesday, May 12, can spot the feeble blue-green light of Neptune. The nearby crescent moon acts as a convenient guidepost, as the two objects will be separated by only 6 degrees—a little more than the width of your three middle fingers held at arm’s length.
The most distant gas giant in the solar system lies so far away from Earth that sunlight reflecting off its upper cloud deck takes about 251 minutes to reach us. Shining at only 7.9 magnitude, Neptune is too faint to see with the naked eye. Sky-watchers will need at least binoculars to catch a glimpse of it as a faint blue-tinged star, but the planet is best hunted down with a backyard telescope. Under high magnification, the distant giant will be an obvious tiny disk with distinct coloration against a backdrop of fainter pinpoint stars.
Saturn and the scorpion’s claw. On Wednesday, May 13, look for Saturn shining brightly in the lower southeast evening sky. Tonight it will be joined below by the bright star Beta Scorpii, also known as Graffias, which means ‘claws’ in Arabic. The pair will be less than 2 degrees apart—a little more than the width of your thumb held at arm’s length.
Graffias is actually a double star, and it is worth looking at more closely because the pair of suns, shining at magnitude 2.5 and 4.9, can be seen with the naked eye. Located about 530 light-years from Earth, the two stars are 2,200 times farther apart than Earth is from our sun, and they orbit each other every 16,000 years.
Leo Triplet. On Friday, May 15, evening sky-watchers with telescopes can benefit from the dark moonless sky and hunt down a tight trio of galaxies hanging on the hindquarters of the constellation Leo, the lion.
Start your hunt east of the Sickle formation that forms the head of Leo. Known as the Leo Triplet, Messier 65, Messier 66, and NGC 3628 are a trio of interacting spiral galaxies located just south from third-magnitude Theta Leonis, known also as Chertan. Theta Leonis marks the bottom right corner star of the stellar triangular pattern that forms the rump of the lion.
Although Leo appears deceptively barren to the naked eye, its location in the sky is far enough away from the dust and star clouds of our own Milky Way to let us peer at galaxies outside of our own. In the case of the Leo Triplet, these galaxies collectively sit about 35 million light-years from Earth, and their disks are tilted at various angles from our line of sight. NGC 3628 is seen edge-on, with thick dust lanes along the plane of the galaxy while M65 and M66 are tilted such that their spiral arms are visible.
The asteroid Herculina. After nightfall on Sunday, May 17, look toward the southeast for asteroid 532 Herculina as it reaches its biggest and brightest point in our skies for the year. The ninth-magnitude space rock is now gliding across the backdrop of stars within the constellation Serpens, the snake between the bright orange-colored star Arcturus to its north and yellow-hued Saturn to its south.
Herculina is currently 3 degrees southeast of the the faint naked-eye, 3.7 magnitude star Epsilon Serpentis, which should make it easy to hunt down with a small backyard telescope. This 230-kilometer-wide space rock is among the 20 largest asteroids known to reside in the main belt of asteroids lying between the orbits of Mars and Jupiter.