StarWatch: Moravian College Astronomy

StarWatch for the greater Lehigh Valley

JULY 2016

JULY STAR MAP | MOON PHASE CALENDAR | STARWATCH INDEX | NIGHT SKY NOTEBOOK

Print Large Sky Charts For 10 p.m. EDT: NORTH | EAST | SOUTH | WEST | ZENITH

Current Solar X-rays:

Current Geomagnetic Field:

1037 JULY 3, 2016: Dippers are American as Apple Pie: During the month of July we are going to take a tour of the early evening sky, starting in the north and proceeding counterclockwise to the east, south, west, and finally overhead. This week’s map can be printed by going to the URL http://astronomy.org/StarWatch/maps/2016-07-15-2200-N.gif With the new moon occurring on Independence Day, it’s impossible not to think Americana this week, and the best example in the sky is our own Big Dipper which is really a part of the constellation of Ursa Major the Great Bear. There is a rather shaky legend that the Dipper, actually the antebellum South’s Drinking Gourd, helped slaves from Alabama find their way north to freedom in Ohio. The Drinking Gourd song seems more a part of fanciful imaginations than actual fact, and you can formulate your own opinions by visiting http://www.followthedrinkinggourd.org/ The Dipper by 10 p.m. is mid-sky in the NNW, with its handle up and cup down. Dubhe (right) and Merak, the two lowest stars, point to the Pole Star, Polaris, which serves adequately as the pivot point around which the sky circles. The motion is simply a reflection of the Earth’s own rotation; so if you go out a few hours later, you’ll note the Dipper lower and other stars in the east higher. Polaris ranks as the 48th brightest star in the nighttime sky, but it is bright enough to be seen easily on a moonless night from suburbia. A majority of Americans feel that Polaris is the brightest star of the night, but its luminescence does not make it famous. You might call it the Zen star, quietly meditating in stillness, the anchor of the pivoting heavens. Polaris is, however, the brightest star at the end of the handle of the Little Dipper (Ursa Minor), which is now handle down, cup up. Probably the two top stars of its cup, Kochab (left and lower) and Pherkad, will be the only ones visible under suburban lights. You also cannot ignore Draco the Dragon, slinking itself between the two Dippers by 10 pm, its head held high above and to the right of the Little Dipper’s cup. Good observing!

1038 JULY 10, 2016: The Great Summer Triangle: During July, we will be looking at star patterns and other objects that can be witnessed in the 10 p.m. sky seen from suburbia. This week, our focus is luckily towards the east, but first a brief announcement from our moon. “I become the nemesis for everyone wanting to view the starry heavens, for I explode from a fat, horned crescent on Sunday to a bulbous, brash gibbous by the week’s end.” As Luna’s brightness increases 10 fold, the fainter stars begin to fade as the sky becomes awash in brightening moon glow. To the rescue comes the Great Summer Triangle with stars bright enough to laser their light through the haziest of moonlit evenings during the summer. On occasion they are the only three stars visible in the night. Not a constellation by themselves, they represent the alpha stars of three patterns—Deneb, the faintest of the group and a member of Cygnus the Swan; Altair of Aquila the Eagle; and the brightest of the triad, Vega of Lyra the Lyre (harp). Before astronomers were able to obtain rudimentary stellar distances, there was a natural assumption to consider the brighter stars closer and the fainter ones farther away. The concept of finding stellar distances was easy to understand. Hold your index finger about six inches in front of your nose and wink your eyes back and forth. Your finger will appear to jump, a result of the different views created by each eye over the baseline (distance) between them. Hold your finger farther away, and the displacement becomes less. When techniques became refined enough to accomplish this same feat with the stars, the Great Summer Triangle yielded a surprise. Deneb, the faintest of the lot, but still bright, turned out to be a powerhouse star, 1600 to 3200 light years distant. The energy from Deneb entering your eyes left its source between the time that Rome and Egypt ruled the known world. Vega and Altair were, ho hum, 26 and 16 light years away, respectively. Look east, mid-sky at 10 p.m., to view the greatest triangle of them all, the Great Summer Triangle.

1039 JULY 17, 2016: Bright Moon Dominates Week: It’s mid-July, and our focus this week shifts to the south where some of the best summer constellations await the passing of the moon which will be full on the 19th. While the bright moon dominates most of the week hiding the stars of Scorpius the Scorpion and Sagittarius the Archer, Luna in itself is an interesting object to view and to photograph. When you view the moon in and around its full phase, you’ll notice that its surface can be divided into lighter, irregular areas and darker circular regions. The more reflective highlands represent the original crust that formed on the lunar surface as it cooled from a molten state between 4-4.5 billion years ago. During the moon’s early history, its surface was pounded and pulverized by leftover rubble that was being assimilated by the planets and their natural satellites. This early bombardment period tapered off rapidly, but not before the moon was struck by some truly titantic objects sent sunward by the outer planets or through collisions which scattered debris outward from the asteroid belt. The end result was the formation of the basins, huge craters gouged from the moon’s surface by these collisions which occurred about 3.85 billion years ago. Over the next 800 million years, subsurface magma slowly filled these craters, layer upon layer to their present levels. Since then, the surface has been peppered by smaller debris that the moon has encountered. With binoculars it is possible to see some of these more recent impacts as the brighter craters and ray systems fanning outward from these collisions. The moon over eons of time has become less reflective as it has swept up extremely small bits and pieces of darker silicate material, mainly released by comets in their passages around the sun. When a larger meteorite strikes the moon’s surface, the debris thrown from the crater churns up or “gardens” the soil to expose the more reflective material underneath it. We return to the stars and the planets in the moonless south and west next week.

1040 JULY 24, 2016: Planets Gleam in Moonless Sky: The next two weeks offer an excellent opportunity to view the sky under moonless conditions. About 30 minutes after sundown as the blue sky of day is fading to gray, look low in the west for a bright starlike object shining with a steady light. That will be Jupiter paying its last respects as the sun nears and hides Jove by mid-August. Jupiter will again become prominent in October 2016, but low in the eastern morning sky. Two other planets are worth noting, Mars and Saturn, just west of south as daylight fades. Mars will be the brighter of the pair and will be distinctly orangey in hue while Saturn will appear more yellowish-white. They dominate the south and SW during the early evening hours and will remain visible for many months. Saturn becomes difficult by late October, but Mars hangs around through May of 2017 when Jupiter will again be prominent, but this time in the early evening east. Directly below Saturn is one of my favorite luminaries, Antares, which is the alpha star of one of my favorite constellations, Scorpius the Scorpion. Antares is Greek for the rival of Ares (Mars), and it is actually a red supergiant star nearing the end of its life. Watch as Mars sneaks up to Antares during the next four weeks. Between August 22-25, brighter Mars will be within two degrees of Antares in the SW as skies darken, a great way to compare their similar colors through binoculars. Under light pollution free skies, the Scorpion is simply magnificent. Three stars to the right of Antares and two stars close to the red supergiant form the head and body of the Scorpion; but it’s the graceful sweep of his tail and the curl of his stinger which sets the scorpion apart from other star patterns and makes it special like Orion the Hunter in our winter sky. Unlike Orion, from midnorthern latitudes the tail and stinger are horizon huggers, visible to observers only under the clearest of evenings and from sites with open southern starscapes. The center of our Milky Way galaxy nosedives into the horizon just to the east (left) of Scorpius.

1041 JULY 31, 2016: High Time for Looking Up: The sky this week remains virtually moonless, and this gives us another excellent opportunity to view some of the fainter star patterns. The focus is overhead. Facing east, the brightest star of the Great Summer Triangle (GST), Vega (see StarWatch for July 10) will be nearing the zenith. Below and to the right of Vega is a small parallelogram of stars that represents the strings of the harp. Just below Vega, and slightly left, is a faint star called Epsilon Lyrae. If you look at it with binoculars, the star will be easily split into two luminaries. A good telescope at about 100 power will split each star into two additional components. It is rightfully named the double-double. To Vega’s left and below is the faintest celebrity of the three, Deneb, which in Arabic means “tail,” the tail of Cygnus the Swan. Do not look for a swan from suburban skies, but imagine a cross lying on its side. The staff of the Northern Cross points along the backbone of the Milky Way, so even if the gossamer star fields of our galaxy are invisible because of light pollution, our galaxy is mentally traceable from its rising position in the NNE to where it meets the horizon in the south. Scanning the Cygnus region with binoculars will reveal how the density of stars increases along the Milky Way’s path, allowing its heavenly arc to be traceable from suburbia on most summer evenings. Facing north about two fists held at arm’s length, to the left of Vega will be Hercules the Strongman (west of the zenith). The four faint stars that outline his torso are the most distinctive and are called the Keystone. Just like the GST, the Keystone is not sanctioned by astronomers as an official constellation, but the pattern is famous enough to have a name. Scan the left side of the Keystone with binoculars, looking for a small condensed fuzzy patch of light. When you find it, you’ll be looking at a globular cluster named M13, an aggregate of over 300,000 old stars, 25,100 light years distant. The photons entering your eyes tonight left M13 when we as a species were first painting animals on cave walls.

[July Star Map]

[July Moon Phase Calendar]