Tuesday, June 23 pre-dawn – Neptune reverses direction
On Tuesday, June 23, distant blue Neptune will cease its regular eastward orbital motion through the background stars (red path) and begin a retrograde loop that will last until late November. On this date, you’ll find the blue-green, magnitude 7.9 planet in eastern Aquarius, sitting a palm’s width to the upper right (or 6.5 degrees to the west) of Mars and 3.5 degrees east of the medium-bright star Phi Aquarii. During the coming months, Neptune will move toward that star.
Tuesday, June 23 after dusk – Crescent Moon buzzes the Beehive Cluster
In the west-northwestern sky after dusk on Tuesday, June 23, the young crescent Moon’s orbital motion (green line) will carry it closely past the northern edge of the large open star cluster known as the Beehive, or Messier 44, in the constellation of Cancer, the Crab. Observers in the Central and Mountain Time zones will be able to see the Moon and the cluster while they are higher in the sky. The Moon encounters this cluster frequently because the Beehive is located only 1 degree north of the ecliptic (green line). The reduced brightness of the crescent Moon should allow you to see the cluster’s stars and the Moon in the field of view of your binoculars (red circle).
Saturday, June 27 evening – The Summer Triangle arrives
After dusk in late June, Vega, Deneb and Altair are the first stars to appear in the darkening eastern sky. Those three bright, white stars form the Summer Triangle asterism — an annual feature of the summer sky that remains visible until the end of December. The highest and most easterly of the trio is Vega, in Lyra. At magnitude 0.03, Vega is the brightest star in the summer sky, mainly due to its relative proximity to the Sun — it’s only 25 light-years distant. Magnitude 0.75 Altair, in Aquila, occupies the southern corner of the triangle. Altair is 17 light-years from the sun. By contrast, Deneb, which shines somewhat less brightly at magnitude 1.25, is a staggering 2,600 light-years away from us; but it ranks so high in visible brightness because of its greater intrinsic luminosity. The Milky Way passes between Vega and Altair and through Deneb, which sits high overhead as dawn begins to break.
Sunday, June 28 at 8:16 GMT – First Quarter Moon
The moon will reach its first quarter phase on Sunday, June 28 at 4:16 a.m. EDT, or 8:16 GMT. At that time, the relative positions of the Earth, Sun and Moon will cause us to see the Moon half-illuminated on its eastern (right-hand) side. Sunlight striking the Moon at a shallow angle produces spectacularly illuminated landscapes along the pole-to-pole terminator line that separates the lit and dark hemispheres. First quarter moons always rise around noon and set at midnight, so they are visible starting in the afternoon hours. The term “first quarter” refers not to the Moon’s appearance, but the fact that our natural satellite has now completed one quarter of its orbit around Earth, counting from the last new Moon.
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.