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On tap in the summer night’s sky

April 30, 2013
By Aileen O’Donoghue , Adirondack Daily Enterprise

This column, like the glittering stars of winter, disappears abruptly when the evenings lengthen. So let me tell you a bit about the celestial events that will occur before The

Wilderness Above returns in the late autumn.

Jupiter, in spite of its eastward motion relative to the stars, has been slowly making its way west as the Earth's orbital motion shifts our nighttime sky about one degree eastward each day.

Article Photos

Tonight it will emerge from the dusky sky about 30 degrees above the western horizon and set three

hours after the sun at 11:20 p.m. Through May it will sink lower in the sunset sky as bright

Venus climbs up to meet it.

On May 15, Jupiter will be 20 degrees above the horizon at sunset and set two hours after the sun. Venus will appear before Jupiter since it will be much brighter than the giant planet by then, and be 10 degrees closer to the horizon. Even closer to the horizon, Mercury will rival Jupiter in brightness, but be very hard to spot in the glare of dusk before it sets a mere 25 minutes after the sun.

By May 26, however, as shown in Figure 1, Mercury and Venus will have climbed up to greet Jupiter and form a close trio between the horns of Taurus. Due to its faster orbit, Mercury will have climbed past Venus and Jupiter to top the trio and be brighter than Jupiter sandwiched between it and Venus. Only 10 degrees (the width of your fist held at arm's length) above the horizon as the sun sets, there will be a little more than an hour to spot this lovely configuration before it, along with Orion's club, seeming to wave goodbye, sink below the horizon, themselves.

If you have a chance to spot it, also take note of the two stars marking the end of Orion's club, Chi-1 and Chi-2 Orionis. These stars appear very similar in our sky, but are actually very different. Chi-1 is a star very much like our sun only 28 light-years away. Thus the light we see this year left Chi-1 in 1985. Chi-2, however, is thought to be 4,900 light years away so that the light from it has been traveling since 2887 BC! To appear as bright as nearby Chi-1, Chi-2 has to have a luminosity 410,000 times greater and a size about 60 times greater than the sun.

With a size 70 percent that of Mercury's orbit, it is actually a hypergiant only five million years old that will end within a few more million years in a supernova explosion that may crush its core

into a black hole. Though a few million years is quick on the astronomical time scale, our lives are far too short for us to hope to witness this spectacular event though it may, in fact, have happened a thousand years ago and the information will still take 3,900 years to reach us!

Figure 2 shows the southern sky of late summer when the glittering plane of the Milky Way galaxy arches high over the Adirondacks. Two beautiful constellations, Scorpius and Sagittarius, mark the region toward the galactic center. Just above Ptolemy's cluster, slightly

left of the Teapot's spout, is the spot where a supermassive black hole, four million times more massive than the sun, lurks at the center of our galaxy, 30,000 light years away. In order to measure its size and mass, astronomers have used infrared and radio telescopes to observe the orbits of nearby stars. Some of these stars will eventually fall into the black hole as millions have done in the 13.2 billion years since the Milky Way formed. It is now thought that every large galaxy has a supermassive black hole in its center, some of which give rise to jets of radioluminous plasma squeezed out like toothpaste as matter crowds in toward the center pulled by immense gravitational forces.

Closer to Earth, if you go out to observe the Perseid Meteors on Aug. 12, the sky offers a variety of visible delights to the unaided eye as well as binoculars and telescopes. The waxing crescent moon will be just below Saturn as the southwestern sky darkens. After its close approach to Kappa Virginis in July, Saturn will be speeding up as it moves back toward Libra.

The moon's quicker motion will place in Libra the very next night when it will be about a degree

below Zubenelgenubi (Zoo-ben-el-gen-NEW-bee). On the 12th, the moon will set by 11 p.m., increasing the opportunity for spotting meteors as our region turns to face in the direction of Earth's orbital motion at midnight. Unfortunately, Scorpius also sets, so take time early in the

night to explore this region with binoculars or a telescope as tolemy's and other clusters along with the Lagoon and other nebulae (glowing gas clouds) provide beautiful sights.

Watching for meteors without binoculars is a good time to pick out one of the more obscure constellations, Ophiuchus (Oaf-ee-YOU-kus, though some drop the second syllable), the Snake Bearer and his snake, Serpens. To find Ophiuchus, first look nearly straight up to locate the Keystone of Hercules between Corona Borealis and bright Vega (VEE-guh). The western (right)

side of the Keystone is a guide to another binocular & telescope prize, M13, a globular cluster of hundreds of thousands of stars 145 light years in diameter and nearly as old as the galaxy.

Those with excellent eye sight and a very dark sky (after moonset) can see this cluster without binoculars. The Keystone is Hercules' hips and he's down on one knee, upside down in our sky.

His forehead is marked by Rasalgethi (Ross-all-GAY-thee with the "th" as in "thin") that leads

the way to Rasalhague (ROSS-all-hog) marking Ophiuchus' forehead. From there, look for the arc of stars from Sabik (SOB-ick), Han (rhymes with yahn), and the Yeds prior and posterior, the front and back of Ophiuchus' hand (holding the snake). These mark the bottom of the constellation and lead westward (right) to the serpent's head which is a fairly distinctive triangle. Eastward (left), the serpent's tail ends at Alya (ALL-yah), near Aquila.

Aquila's brightest star, Altair (Al-TEAR, rhymes with bear) is the southern apex of the Summer Triangle that also includes Vega in Lyra (LYE-ruh) and Deneb (DEN-ebb) in Cygnus, the swan. Just after midnight, Deneb will be very near the zenith so if you're still watching for meteors in a chaise lounge or hammock, lean back and savor the sparkling sights (with or without binoculars) of this vast cosmic bird gliding through our summer skies.

Beyond this column, local astronomers are anxious to share our love of the sky with you.

Check out the Adirondack Public Observatory web site at apobservatory.org for events. Listen

for me on North Country Public Radio about once a month during "The Eight O'clock Hour" oremail me with any questions at aodonoghue@stlawu.edu.

 
 

 

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