Sky Roundup: May, 2008

Close Calls
The skies over Cleveland in the month of May show us a number of close encounters of the Moon with planets, stars, and star clusters.  Among the planets, these encounters are not uncommon since the Moon skirts in the vicinity, that is, close to the ecliptic, where the planets generally are seen to move.  Bright stars and star clusters coincidentally also find themselves near the Moon’s passage across the sky.  Not just the Moon but planets, too, have close calls with star clusters.

For example, on May 2nd, the planet Mercury appears to move close to the star cluster known as the Pleiades.  The small, hot inner planet moves within 2° of the pretty, distant cluster, as we attempt to glimpse in evening twilight (around 9:30 p.m.), but it may be too close to the horizon to see clearly unless you’re standing on the eastern shore of Lake Erie and have a cloud-free view to the west.  A telescope or a very good binocular will help.  Within days, too, the Moon in its waxing crescent phase, appears close to Mercury, and may only be visible under the same conditions as it’s so close to the horizon on May 6th.  (See chart.)

In early May, the slim crescent Moon hangs with hot little Mercury toward the western horizon after sunset.  Conditions need to be ideal, such as an unobstructed horizon and good optical aid to see both of these objects in evening twilight.

On May 10th the small cold world of Mars appears to get a visit from the waxing crescent Moon; they appear close together in the sky.  There is an occultation of Mars visible across parts of northern Africa; unfortunately, we cannot see this close call in our skies.  By about 9:00 p.m. that same evening, the Moon gradually brushes past the Beehive Cluster (also known as M44), and this apparition we can see from Cleveland. 

Two evenings later on May 12th, after the Moon enters its First Quarter phase, it has a close encounter with the bright star Regulus, the heart of Leo (the Lion).  Appearing just over 1° from the Moon, Regulus this month is occulted by the Moon, as it was last month, but, as before, that occultation is not visible from Cleveland. 

Another encounter, even closer than the Moon with Regulus, occurs with the gibbous Moon and the bright star Antares on May 20th.  A similar apparition occurred last month and an occultation was the result; like last month, too, this month’s occultation is only visible from portions of the Southern Hemisphere.  Occultations of Antares can be particularly interesting though, since, on rare occasion, the body of the Moon blocks Antares in a manner that can allow the observer to see the small, faint, white companion of that big, bright, orange star.  (See Sky Roundup, May 2007, for a description of an occultation of Antares.)

The planet Neptune also has a brush with our lunar neighbor on the evening on May 26th.  For observers in portions of northern Africa and southeastern Europe, the waning gibbous Moon appears to hide that distant planet, but, for us in Cleveland, it’s another close encounter and no occultation is seen.

Well, then, with all of these close calls, is there any direct hit for us to see here?  Indeed, there is!  On the evening of May 22nd the Red Planet scores a bull’s-eye with the Beehive Cluster.   About two hours after sunset for us in Cleveland, Mars appears to glide right through that pretty, fairly bright, open cluster of stars.  Weather permitting, this is definitely a fine sight for a good binocular, a real treat with a wide-field telescope, and a good test of performance for a camera.  (See chart.)

Mars seems to glide right through the Beehive Cluster (M44) on May 22nd after sunset.  A telescope or good binocular will show a fine sight.

Another direct hit is with the planet Mercury all on its own.  The small hot world reaches its greatest elongation (that is, its greatest angular distance from the Sun as seen from Earth) on May 14th.  This means that just after sunset, local time, observers should be able to glimpse Mercury low in the west; this should be its best apparition for the entire year as its position in the early evening sky favors those observers in the Northern Hemisphere.

Venus appears to have its own close call with the Sun as it heads toward superior conjunction, so it’s lost in the glare of the Sun for all of us observers on Earth.

But one celestial phenomenon that won’t be lost to our view is the peak of the Eta Aquarid meteor shower.  On the evening of May 5th, the New Moon will ensure dark skies, which should be a suitable backdrop to see the meteors known as the Eta Aquarids.  The name signifies the radiant, or vanishing point (near the star designated star Eta in the constellation Aquarius), from which these meteors appear to stream across the sky. 

Meteors that we see flash across the sky are themselves the debris left in the wake of a passing comet; in this case, the source for this particular meteor shower is none other than the famous Comet Halley.  According to newspaper accounts of its day, that comet had a close call with Earth ninety-eight years ago.  In its usual 76-year orbit, the comet happened to cross the plane of the Earth’s orbit in 1910.  During that particular return to the vicinity of the Earth, the comet was a spectacular sight and was the subject of many classic black-and-white photographs.  The Earth’s eventual passage through the diffuse tail of the comet gave way to widespread alarm, especially when traces of cyanide were detected in the comet’s tail, which some feared might poison our whole planet.  That close call presented no danger to Earth.

In our present-day night sky, Jupiter and Saturn have appeared relatively stationary, owing to their slower orbital motion relative to Earth’s faster clip around the Sun.  By mid-month, Jupiter rises in the east-southeast in late evening and majestically marches across the sky for the rest of the month.  It is in close proximity north of the Moon on May 24th.  In close quarters to Regulus all month, Saturn puts in an appearance high in the south-southwest by the end of evening’s civil twilight and then sets in the west-northwest by the start of the following morning’s astronomical twilight.

Observations in astronomy aren’t always spot-on one-of-a-kind alignments for all of us to enjoy; often from our vantage we get just a glimpse of how planets and stars can appear so close together and still be so far apart.  Nevertheless, even the close calls we’re privileged to witness are unique views from our perspective.

Sky Roundup Almanac for Cleveland, May, 2008

May   2: Mercury 2° south of Pleiades (M45)
May   5: New Moon; peak for -Aquarid meteors
May   6: Waxing crescent Moon less than 1° north of Pleiades
May 10: Mars less than ½° from tBe waxing gibbous Moon (no occultation seen)
May 11: Moon less than ½° from the Beehive Cluster (also known as M44)
May 12: First Quarter Moon; Regulus just over 1° north of Moon
May 14: Mercury at greatest eastern elongation, seen in west at sunset
May 20: Full Moon (smallest in 2008); Antares less than ½° north of Moon
May 22: Mars seen within the Beehive Cluster (M44)
May 24: Jupiter 2° north of waning gibbous Moon
May 27: Neptune just over ½° south of Moon (no occultation seen in Cleveland)
May 28: Last Quarter Moon

Questions or comments?
Please contact:  Roy Kaelin at (216) 231-4600, ext 3405, or rkaelin@cmnh.org