The Sky This Week, 2013 June 18 - 25
The "Honey Moon" rising, 2010 June 22
The Moon brightens the overnight hours this week, waxing to the Full phase on the 23rd at 7:32 am Eastern Daylight Time. As she progresses eastward against the stars she also dives down to the southernmost reaches of the ecliptic. If the air is sultry and hazy this may give Luna a somewhat warmer tint than her usual dazzling white glow, which may be why this particular Full Moon is popularly known as the Mead Moon, Rose Moon, or Honey Moon. The latter, of course, may be one of the reasons that June is a popular month for weddings. Another popular name is the Strawberry Moon, since this is the peak of the short strawberry harvest season. Look for the Moon just three degrees east of the bright star Spica on the evening of the 18th. On the 19th she is seven degrees southeast of yellow-hued Saturn. On the 21st Luna courses six degrees north of the bright star Antares.
In recent years much hay has been made over a phenomenon popularly called the "Super-Moon". This term was coined fairly recently to describe the coincidence of the Full Moon with the year’s closest lunar perigee, and it happens to occur this month. In fact, perigee occurs just 20 minutes before the instant of Full Moon at a distance of 356,991 kilometers (221,824 miles). While some people claim that this makes the Moon appear exceptionally bigger and brighter than "normal", I have never noticed such effects. The only thing that makes the Moon appear larger to me is the well-known "Moon Illusion", where the apparent size of the Moon’s disc is distorted by its proximity to objects on the horizon when it is either rising or setting. This year many people may think the Moon looks bigger, but the Full Moon is never more than 30 degrees above the Washington horizon, inviting the Moon Illusion to play its tricks on all of us.
Summer officially begins on June 21st at 1:04 am EDT. At this time the Sun will be located directly overhead along the Tropic of Cancer at a point along the border between China and Vietnam. Here in Washington we’ll see our longest duration of daylight for the year with Old Sol above the horizon for 14 hours 54 minutes. However, we won’t quite see the year’s latest sunset on the 21st. Thanks to our need for keeping a mean time-scale and the elliptical orbit of the Earth that event won’t occur until the 28th. While most of us probably haven’t noticed, the earliest sunrise occurred back on June 14th. On the 21st sunrise will occur a full two minutes later.
Evening twilight is the time to start looking for planets as spring turns to summer. On a good clear evening you should have no trouble picking out Venus within a half hour of sunset. She is slowly making her way eastward from the Sun with each passing evening, and she will be a steady fixture right after sunset for the rest of the year. Over the first few days of the week she passes within two degrees of the elusive planet Mercury. You’ll need to wait until at least half an hour after sunset and use binoculars to spot Mercury, which is now beginning to take a sudden plunge toward the Sun. The fleet planet will be located just to the left of Venus on these first few evenings, and then the two worlds will rapidly part company. If you can get a telescope on Mercury before he sets, watch his phase shrink as a waning crescent. We had an excellent view of this little-seen world at the recent "Astronomy Night on the National Mall" program.
Once Venus and Mercury have departed the scene you should be able to see Saturn in the fading vestiges of twilight. Saturn forms one apex of a large elongated triangle in the sky with the other corners marked by the bright stars Arcturus and Spica. You should be able to tell the planetary nature of Saturn by comparing the three objects in your binoculars. The stars will still be bright pinpoints of light, but Saturn will appear as a tiny oval. Of course the real treat is to see Saturn through a telescope. No matter how many times I look at it through mine, I still have to convince myself that it’s real!