Thursday, May 21 after sunset – Mercury passes Venus
In the northwestern sky after sunset on the evenings of Thursday, May 21 and Friday, May 22, the orbital motions of Mercury and Venus (curved lines) will bring the two planets close together. On Thursday, Mercury will be a finger’s width below (or 1 degree to the celestial southwest of) Venus. Since Venus is descending while Mercury is climbing, on the following evening Mercury will move to Venus’ upper left. The two planets will be easily told apart, since Venus will appear nearly 30 times brighter than Mercury. When viewed in a backyard telescope, Mercury will show a nearly fully illuminated disk, while Venus will show a very slim crescent (insets). This difference in illumination is happening because Venus is passing between Earth and the sun while Mercury is on the far side of the sun. Look for the main belt asteroid Vesta located less than 5 degrees to the southeast of the two inner planets.
Friday, May 22 at 17:39 GMT – New Moon
At its new phase on Friday, May 22 at 17:39 GMT, the Moon will be travelling between the Earth and the Sun. Since sunlight is only shining on the side of the Moon aimed away from us, and the Moon is in the same region of the sky as the sun, the Moon is hidden from view everywhere on Earth for about a day.
Sunday, May 24 pre-dawn – Dwarf planet Ceres near Mars and Neptune
In the southeastern pre-dawn sky on the mornings surrounding Sunday, May 24, the west to east orbital motion of the dwarf planet Ceres (red path with labeled dates/times) will carry it a generous palm’s width below (or 7 degrees to the celestial south of) Mars. The asteroid will shine at magnitude 8, much dimmer than Mars’ magnitude 0.1 – however, Ceres should be readily visible in binoculars (red circle) if you use the stars Skat and Tau Aquarii to help you locate it. Less than two binoculars fields to the left of Mars, distant Neptune will be shining with the same intensity as Ceres. Look for that blue planet sitting just a few degrees to the lower left of the star Phi Aquarii.
Sunday, May 24 after sunset – Young Moon, Mercury and Venus
The waxing crescent moon will join Mercury and Venus in the west-northwestern sky after sunset on Sunday, May 24. Look for the moon’s slim crescent sitting a fist’s width to the upper left (or 11 degrees to the celestial east) of very bright Venus, with much dimmer Mercury between them. Venus will set first, shortly after 9:30 p.m. local time.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the universe together.