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The Sky This Week, 2013 April 30 - May 7

May Day, spring stars, and Saturn!
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Saturn at opposition, 2013 April 28, 04:06 UT
Note the three moons and rings brightened by the "Seeliger Effect"


The Moon wanes in the morning sky this week, greeting early risers as she passes through the star-poor reaches of the rising autumnal constellations. Last Quarter occurs on May 2nd at 7:14 pm Eastern Daylight Time. Luna encounters no bright objects along her path this week as she whittles away to a slender crescent in the morning twilight by the week’s end.

For most of us May 1st is simply the start of another month, albeit one of the best months of northern springtime. Once quite widely observed in the U.S., "May Day" fell out of favor with the rise of socialism in the early 20th Century as the day became more universally observed as International Workers’ Day. These traditions are merely riding on the shoulders of a very ancient fertility celebration that happens to have an astronomical origin. May 1st happens to fall midway between the vernal equinox and the summer solstice, and so was widely observed as the traditional beginning of summer. To the ancient Celts it was known as Beltane, and much of Europe under Roman rule observed it as the festival of Flora, goddess of flowers. As Christianity spread through Europe the Germanic tribes adapted the celebration to "Walpurgisnacht" in honor of Saint Walpurga, who was canonized on May 1, 870. May Day is still widely observed in Europe and South America, and in many cases it’s an official holiday. Characterized by dancing around a May pole, the crowning of May Queens, and general revelry, its ties to those ancient fertility rites may still be glimpsed today. May Day is a so-called "cross-quarter" day that is associated with the more traditional seasonal markers that were once the traditional days for serfs to pay rent to their feudal masters. Today we still celebrate two other cross-quarter days when we go trick-or-treating for Halloween or await the prognosticative powers of a large indigenous rodent on Groundhog Day. The final cross-quarter day, Lammas, which falls on August 1st, is now largely forgotten.

The absence of the Moon from the evening sky now begins to allow us to once again explore the more subtle sights of the springtime constellations. The flashy stars of winter now meet the western horizon as twilight ends, leaving behind a sky full of generally fainter stars. These stars form some very familiar patterns, though, and by 10:00 pm you should have no trouble spotting the Big Dipper and Leo, the Lion on the meridian nearly overhead. To the east you’ll see the bright rosy star Arcturus, and to the southeast the bright star Spica followed by the golden glow of Saturn. The general area of the sky bounded by these objects is the "Realm of the Nebulae", the heart of the Virgo Galaxy Cluster. Point a six-inch aperture telescope at almost any spot in this part of the sky from a dark location and you’re almost sure to run into the fuzzy smudge of light that betrays one of these many distant places.

Bright Jupiter now dips below the horizon well before 11:00 pm. He still dominates the western horizon as soon as evening twilight begins, but getting a good view of him through the small telescope is becoming increasingly difficult as his light passes through more of our atmosphere. His apparent disc has also become much smaller, and now subtends just 33 arcseconds, as opposed to his maximum of 48 arcseconds at opposition.

Saturn quickly steps in to fill Jupiter’s void. The ringed planet has just passed his opposition, so he rises just before sunset and is in the sky all night long. By 10:00 pm he should be high enough to get a good look in the telescope, and as he heads toward the meridian for transit just after midnight he should give you several hours of observing enjoyment. The planet’s rings are tipped about 20 degrees to our line of sight, and a good three-inch telescope should show the gap in their outer edge known as Cassini’s Division. This gap is caused by a gravitational resonance between several of the planet’s inner moons. This resonance causes periodic disturbances to any ring particles that happen to stray into the gap area. To give you a sense of the scale involved, the gap is about as wide as the diameter of the Earth!

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