Gaze skyward this week and watch our solar system’s two innermost planets have a strikingly close encounter, while changing seasons brings the year’s largest moon in the sky.
Moon and Spica. On Tuesday, June 18, look towards the southern sky to see the gibbous waxing moon glide extremely close to the distant star Spica (263 light years away), which is the brilliant white member of the constellation Virgo.
By nightfall in the western hemisphere, the cosmic duo will appear about 2 degrees apart–equal to about the width of your thumb at arm’s length. From Europe and Asia they will appear even closer, and from southwest Africa and Madagascar the moon will appear to hide Spica.
June Solstice. For the northern hemisphere, summer (winter in the southern hemisphere) officially begins at 1:04 a.m. EDT on Friday, June 21 (5:04 am UT; See list of cities and local times).
During this season, the Earth’s northern axis is slightly tilted toward the sun so that the northern hemisphere gets more direct sunlight and experiences warmer temperatures. Locations south of the equator are tilted away from the sun, so that the sunlight is dispersed, making for colder temperatures.
For skywatchers on the first day of the new season and a few days afterward the sun appears to rise at the same place on the horizon – hence the origin of the word solstice, meaning ‘sun stands still’ in Latin.
Saturn Meets the Moon. On the evening of Wednesday, June 19, the moon will glide underneath the ringed-planet, less than 4 degrees apart–less than the width of your three middle fingers at arm’s length.
It’s amazing to think that despite its mind-boggling 1.38 billion kilometer (857 million mile) distance from Earth, humans have the Cassini spacecraft orbiting the planet and its retinue of moons.
Venus and Mercury Pair Up. Also just after sunset on June 19 check out the two innermost planets in the solar system close together one last time as Mercury begins to sink back closer to the sun and drop out of sight. Face the northwest sky about 30 minutes after sunset and look very close to the horizon for the final meeting of brighter Venus and little Mercury to its left.
The planetary pair will be about 2 degrees apart, making for a cool sight through a small telescope. Mercury will appear as a thin crescent while Venus will look much like a miniature version of a gibbous moon, with nearly 94% of its disk lit.
Biggest Supermoon of 2013. Only two days after the solstice, in the early morning hours of Sunday, June 23, the moon will officially reach its full phase and will be the closest (356,990 kilometers or 221,823 miles) and largest ‘supermoon’ of the year.
The moon’s orbit is egg-shaped, and there are times when it is at perigee—its shortest distance from Earth in the roughly month-long lunar cycle—or at apogee, its farthest distance from Earth. If the full moon phase happens to be at the same time as the perigee then we get a supermoon, which happens once a year.
Despite all the media hype in recent years, the difference in size of the lunar disk from ‘average’ full moons will be so negligible that most moon gazers will not notice anything amiss. Still, there is nothing quite as magical as watching that giant silvery orb rising in the east after sunset.
Tell us—what amazing sky phenomena have you seen lately?