Larry’s     New Braunfels Astronomy Club, Texas, USA
 Celestial Calendar & Newsletter
            April 17, 2008, to May 15                                                                      132nd monthly edition
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 A new edition of this Newsletter is posted on our Website by the third Thursday of each month
 
All of our references to the times of sun and moon rising or setting, moon phases, and
morning or evening astronomical twilight starting or ending, are from the U.S. Naval Observatory’s data for Sattler, Jellystone Park, Canyon Lake and New Braunfels in eastern Comal County, Texas.
 
“May places a slew of planets on view”
                                                  ----and Mercury looks about as good as ever, says Astronomy
 
Welcome to the cyberspace Astronomy Club. We’re saying “So long, see you later” to the  constellations Orion, Taurus and Perseus as they dip below treetops in the west by nightfall, but then we’re greeting Hercules, soon to reach 20˚ high in the east, to be followed later by Lyra, Serpens and Cygnus. And another special arrival will be the magnificent globular cluster
Omega Centauri, the biggest and brightest in our galaxy.  
 
We’ll see the first signs of the 2008 meteor shower season, with at least sporadic glimpses
of four showers of tiny debris left in the wake of passing comets. (See details, following.)
 
Luna will reach full illumination as the Egg Moon, or Grass Moon, at 5:25 a.m. this Sunday, thereafter fading to third-quarter at 9:12 a.m. on April 28; to new moon at 7:18 a.m. on May 5,
then to first-quarter phase at 10:48 p.m. on May 11.  
 
Here’s a rundown of activity during these next four weeks, from now until Thursday, May 15:
 
Thu Apr 17   sunset 8:01  dark 9:24                  The king of globulars cometh
The largest and brightest globular star cluster in our entire galaxy, Omega Centauri, is showing
up now in our southern sky, very low in the south-southeast by 11 tonight and slowly gaining altitude as Earth’s rotation moves this object westward across our sky.
 
Omega Cen hugs the southern horizon, never climbing higher than about 11˚ from our south-central Texas vantage point; for most of the nation, it’s totally out of view. But our star party host, Yogi Bear’s Jellystone Park, 10 miles west of New Braunfels, provides us with a very good,
low-horizon view in that direction. We should see Omega just fine!
 
This giant cluster of 10 million stars, nearly the size of a small galaxy, is only 15,000 light-years away. Looking bigger than the full moon, it is easily seen with binocs and spectacular in any telescope. Omega, cataloged as NGC 5139, will be visible directly to our south, 10˚ high, by midnight May 8, then by 11 p.m. May 23, 10 p.m. June 7, and 9 p.m. June 22. Clear of
Jellystone Park’s trees, the unsurpassed globular likely can be seen as late as the middle of
July. When Omega Cen is due south, we’ll see it 36˚ directly below Virgo’s bright star Spica.
 
Tue Apr 22    dawn 5:36    sunrise 6:59         Bad press for Lyrid meteors                    
The Lyrid meteor shower, the year’s second major display of “shooting stars,” ought to be a
quite decent show, with somewhere from 18 all the way to 90 sparklers per hour. But not this
year. What little our sources do say is all negative, and it’s about the bright, glaring moon.
 
Sky Guide, Astronomy, the Abrams Sky Calendar and Ottewell’s Astronomical Calendar
agree  the Lyrids this morning will be “poor,” “spoiled,” “drowned out” by moonlight in this “very unfavorable year for a sometimes strong show.” The meteor stream’s radiant point in Lyra will
be 70˚ high to our northeast an hour before dawn; but the waning gibbous Egg Moon, two days past full, will be only 63˚ away, near Alpha Librae (Zubenelgenubi), up 30˚ to our southwest.
 
Other showers of tiny particles, dislodged by comets as they near the sun, have been seen recently, including the earliest Pi Puppids and Eta Aquarids. A fourth group, the Eta Lyrids,
may leave sporadic streakers as early as May 3.
 
Upcoming dates for this year’s major showers to reach peak brilliance are May 4 for the just-mentioned Eta Aquarids, Aug. 12 for Perseids, Oct. 21 for Orionids, Nov. 17 for Leonids and Dec. 13 for Geminids, according to Sky Guide, the annual pullout supplement produced by Astronomy. But this year, only next month’s Eta Aquarids are expected to earn accolades as
an “excellent” show! (See our note for May 4, following.)  
 
Sat Apr 26     dawn 5:31    sunrise 6:56             Jupiter and the quarter-moon      
“Jupiter and the moon stage a spectacular encounter in the predawn sky” this morning and Sunday morning, says StarDate magazine. The solar system’s largest planet is 99%
illuminated in sunlight, with a bright magnitude -2.4.
 
This morning, 90 minutes before sunrise, according to the Abrams Planetarium Sky Calendar,
the waning gibbous moon is inside the handle of Sagittarius’ Teapot asterism, and Jupiter
hangs 12˚ to the moon’s left. Viewed from our south-central Texas locale, they’re up 30˚ in our south-southeast by 5:25 a.m. Jupiter, home of the four Galilean moons, is about a quarter-turn ahead of us in its outer orbit, more than eight times farther from the sun than we are. The cloudy gas giant exceeds 11 times bigger than our pale blue planet. 
 
“Although opposition and best visibility remain three months away,” says Astronomy magazine,  Jupiter “appears big enough for small telescopes to show lots of detail. Jupiter’s dynamic atmosphere features an alternating series of bright zones and dark belts parallel to the planet’s equator.”
 
This also is one of the best days to study the left side of Luna’s face, the third-quarter features
that include Aristarchus, Kepler, Copernicus and Tycho, plus many other craters, mountains, ridges and the big valleys known as mares, or “seas.”
 
.....Then the best viewing of the right side of the moon’s face -- the first-quarter moon, with help
of the terminator -- might be the five evenings starting Friday, May 9. The first-quarter moon will rise at 12:50 p.m. on May 11, hanging then 50˚ high in our WSW by nightfall.
 
Why are these dates so good for telescopic moon-watching? The Golden Press Skyguide
puts it like this: “As the terminator -- the line separating light and dark -- moves over the [lunar] features, their appearance changes because of the changing angle of illumination. It ‘s along
the terminator that features appear with maximum contrast.” 
 
Sat Apr 26     sunset 8:06  dark 9:31            Saturday nights under starlight
The “stars” of our show are riding into the sunset. We lost Andromeda to the low western haze
last month, and now Perseus, Taurus, Orion and Canis Major are below 20˚ altitude in our west. They will reappear, in predawn skies, in July.
 
But this still leaves us with 10 other good constellations bearing more than 50 Messier and
other objects: Some of the marquee names are the Eskimo and Double Bubble nebulae,
Ghost of Jupiter planetary, Mizar and other binaries, and such galaxies as the Sombrero,
Black-Eye, Whirlpool, Sunflower and Cigar. And yes, there’s the Christmas Tree and numerous other star clusters.
 
The brightest stars guiding us at nightfall will include Dubhe and Alkaid (UMa), Arcturus (Boo), Spica (Vir), Regulus (Leo), Pollux and Castor (Gem) and Capella (Aur). Sirius, in Canis Major, and Betelgeuse, in Orion, stand just above the treetops but are gone before 11 p.m.
 
We hope to schedule another public star party at Yogi Bear’s Jellystone Park Hill Country, the resort-campground 10 miles west of New Braunfels on Hwy 306, for this Saturday or next; but
that needs to be confirmed, and will be announced via emails to members. Our recent events
at Yogi’s have drawn numerous visitors to enjoy the night sky with us. 
 
The other fine, moonless Saturday evening “on our watch” will be next week, on May 3. The
same celestial ballet is featured. Sunset will be at 8:11 and astronomical twilight yields to a
fully dark sky at 9:38. 
 
Wed Apr 30  sunset 8:09  dark 9:35                  Mercury now in the spotlight
Do you have a real good, flat-horizon view of the northwestern sky from your place? If so, you might catch a glimpse of Mercury, just about 8˚ high in our WNW, a half-hour after sunset
tonight. Mercury will hang 4˚ below Taurus’ Pleiades Cluster, to the lower-right of Aldebaran.
Sky & Telescope’s Fred Schaaf suggests finding Mercury and the Seven Sisters in binoculars.
 
Mercury tonight shines brightly at magnitude -1.0, although it’s only 78% illuminated and is 107 million miles away. The innermost planet had its superior conjunction, passing behind the sun, 
15 days ago, and is racing to catch up to us on its inside orbital track. Little better than a third
of Earth’s size, Mercury was photographed very close-up in January by NASA’s MESSENGER spacecraft, which will settle gradually into Mercurial orbit. Many of these new pictures are in StarDate magazine’s March-April edition -- and in May’s Sky & Telescope and Astronomy.
 
Thurs May 1 sunset 8:10  dark 9:36                  Mars makes a Gemini “trio”
“May places a slew of planets on view,” write Martin Ratcliffe and Alister Ling. “Mercury makes
a fine evening appearance early this month as it wanders near the dazzling Pleiades star
cluster. Mars shines like a bright star in Gemini, far above Mercury. And Saturn rides high in
the southwest at sunset.”
  
“The morning sky proves less populated. Brilliant Jupiter rises after midnight in early May, although it comes up in the evening by month’s end. The early-morning sky harbors faint Uranus and Neptune, as well as occasional meteors from the Eta Aquarid shower.”
 
“For a week or so, Gemini morphs from twins into triplets,” the Astronomy writers noted, as
the path of Mars carries it into a nearly perfect straight line this evening with Pollux and Castor
to its right. Then tomorrow night, according to Guy Ottewell’s calendar, planet Mercury will pass within 2˚ south-southeast (meaning to the lower-left) of Taurus’ Pleiades Cluster.
 
Sat May 3      dawn 5:23    sunrise 6:50             A fabulous predawn panorama
This morning’s Saturday predawn sky provides a fabulous observing opportunity -- along with
next weekend, May 10 -- with fully a dozen well-stocked constellations in full view, bearing at
least 65 of our club catalog’s favorite deep-sky objects.
 
If we just mention Scorpius and Sagittarius alone, are you convinced? They’ll both be at their “prime time,” highest they get in the south. If all the rest is merely a bonus, that will include Virgo, Coma Berenices, Cygnus, Canes Venatici and a half-dozen more! Then, before daybreak, Capricornus, Cassiopeia and Andromeda also will rise into our view, here in south-central
Texas.  
 
The moon also rises: A very thin, waning crescent Luna, two days from turning new, might be spotted in Aquarius. It should be up 30˚ southeast at 6:20 a.m., as seen from here.
 
Uranus, Neptune and the asteroid Daphne are among the stars of this show. Pluto is, too, but
the most distant whatchacallit is a faint magnitude +13.9 now -- beyond our telescopes’ range
as it drifts farther out beyond Neptune, 2.8 billion miles now, and not coming back closer for
more than 300 years. We’ll just have to wait.
 
Sun May 4    dawn 5:22    sunrise 6:49             Halley’s children “excellent”
There’s only one meteor shower in this year of 2008 that’s rated for “excellent” prospects -- and why not? It peaks this Sunday morning when the moon is only 26 hours from being “new.” the shower’s sparkling bits of debris are left in the wake of Comet Halley, no less. And its radiant, close to the star Eta Aquarii, will rise to 15˚ in the ESE sky here in south-central Texas an hour before dawn, climbing then to 25˚ high at dawn.  
 
Sky & Telescope, edited in Boston, says these Eta Aquarids “are bright and frequent in the Southern Hemisphere, but few are visible from mid-northern latitudes.” And Astronomy, edited
in Milwaukee, also sees a low altitude for the radiant, and it “will cut the number of visible
meteors significantly.”
 
But Astronomy’s annual “Sky Guide” supplement gives only this shower an “excellent”
prognosis, and says: “Nice spring weather and a moonless night should make this one of
2008’s best showers, producing perhaps 20 to 30 meteors per hour.” Guy Ottewell’s Astronomical Calendar calls this “a very favorable year for Eta Aquarid meteors.”
 
Wed May 7    sunset 8:13  dark 9:41                  Mizar now takes center stage                  
One of our sky’s most fascinating stars will cross due north, up about 65˚ high -- its highest and best viewing position -- at midnight tonight. It is the middle of three stars forming the handle of
the upside-down Big Dipper. This is the fabled Mizar (Zeta Ursae Majoris), recognized as a telescopic binary pair since 1650, according to Burnham’s Celestial Handbook.
  
Mizar is not one of the brightest or nearest stars, but very easily found as part of the Big Dipper. It lies about 78 light-years away, the best-known member of the nearest star cluster: the Ursa
Major Moving Group.
 

Robert Burnham wrote 30 years ago about the star Alcor -- which really sharp-eyed observers

on a dark night, even without optical aid, can see nestled tightly with Mizar -- as a separate

entity, sitting some 1.4 trillion or more miles away from Mizar. He leads us to believe they’re just neighbors and members of the same cluster, traveling in the same direction but not circling

each other.

Some current writers, Astronomy’s columnist Bob Berman and author Craig Crossen

(Binocular Astronomy) among them, do describe Mizar and Alcor as a mutually bound “pair”

of stars: a binary system.

But another astronomer, Jim Kaler of the University of Illinois, is quoted saying, “Precision parallaxes with the Hipparcos satellite show Mizar to be 78.1 light-years away, but Alcor to be 81.1 light-years distant” -- a separation of three light-years, or more than 17 trillion miles! “A separation of over three light-years,” Kaler writes, “almost the distance between here and

Alpha Centauri, would make gravitational pairing unlikely.”

Eventually, it seems, Mizar and Alcor must move far enough through space so it becomes

obvious to all astronomers that they are, or are not, circling each other; or more precisely,

circling their common center of mass. ....This may take awhile.

Meanwhile, back on Earth, in a telescope at moderate magnification, we can see Mizar and

Mizar B quite close together, and the neighbor Alcor farther out, near the edge of view.

 
 
OUR NEXT ASTRONOMY CLUB MEETING: Thursday, May 22, starting at 7 p.m. at the new Unitarian Church building, located at 135 Alves Lane, 0.79 miles toward Seguin from the lights
at the Loop Road (Hwy 46) and I-35. To get there, turn left (north) from Hwy 46 onto Alves, and
the church is within 400 feet up that road, on your left side.    
 
Says Bob Keyser, “I will be out about meeting time to direct everyone into the parking lot,
which is behind the church.  I look forward to seeing everyone there the third Thursday in May.”
  
Dan Riding                                                        Larry Pratt
Chairman                                                                                          Secretary
                         Last updated: Saturday April 26, 2008 10:50 A.M.