StarWatch: Moravian College Astronomy

StarWatch for the greater Lehigh Valley

JULY 2014

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:

933 JULY 6, 2014: Moon Illusion: Not as Big as You Think: This is an excellent week to watch the moon blossom into fullness as well as approach and squeak past the bright planet Mars on Saturday July 5, and then rendezvous with Saturn two days later on Monday, July 7. Both events will occur just after darkness low in the SSW part of the sky. Then, as the moon approaches its full phase on Saturday the 12th, you may want to partake in a test that is called the Moon Illusion. Everyone has seen a full or nearly full moon on the horizon and noted its larger size. The rising moon appears much larger than when it is higher in the sky. Actually, you can prove that the moon really does not change in size by holding a dime at arm’s length and using it to hide the moon when it is in or near its rising position. The fit will be tight. Wait a couple of hours until the moon has gained some altitude and appears smaller. Repeat the experiment, occulting the moon with the dime, and you will notice that the fit will be just as tight as when the moon was close to the horizon. What is happening to convince the mind that the moon appears larger when nearer to the horizon is a conflict between the rational and intuitive parts of the brain. The intuitive brain sees the sky as a flattened dome, believing that objects closer to the horizon are more distant than objects located overhead. In most cases this is true. Puffy clouds offer a good example of this effect. Clouds nearer to the horizon are farther away and appear smaller and foreshortened than clouds which are above an observer. This mindset is transferred to our perception of the sky at night. Because the moon is far away in comparison to terrestrial objects, its size remains basically unchanged. Our rational brain perceives no alteration in the size of the moon whether it is in a rising position or high in the sky. This cerebral conflict causes the brain to interpret the horizonal moon as closer than it actually is, and imagines it to be larger in size.

934 JULY 13, 2014: Spoiler Alert: Watney Smelled Like a Skunk: I generally don’t like science fiction, but when my wife, Susan, plopped The Martian by Andy Weir (Crown Publishing, 2014) in my lap and said, “Read,” I was compelled to take a look. I am a member of the Mars Society and was about to make my third sojourn to their desert research station near Hanksville, Utah to work on the Elon Musk Observatory. “I’m pretty well f**ked,” rants astronaut Mark Watney in his first log entry on Sol 6, his sixth day on the Red Planet. He’s the botanist and space janitor on Ares 3, NASA’s third Mars mission which rapidly goes south and is abruptly aborted during an unforeseen dust storm. Watney gets left behind when the communications dish dislocates and he is taken for a short, but nasty ride and lost in the dust and darkness during the evacuation. With only provisions for about 150 days, Watney’s got to figure out how to survive for several years. His astronaut partners are Earthbound and safe, but there’s no way for him to “phone home.” He could just simply fill his spacesuit with pure nitrogen and die peacefully, but Watney is a survivor and the book becomes a roller-coaster thriller of exhilarating successes and near death experiences that leaves the reader absorbed in the action and rooting for Watney’s survival. He’s got to make water, grow crops, outfit rovers for long distance travel, reestablish contact with NASA, and finally make a 2000 mile journey from Acidalia Planitia to the Ares 4 rendezvous site in the huge crater, Schiaparelli. What makes the book so compelling is that nothing Watney conceives to keep himself alive is beyond the technology which will be incorporated into our human exploration of Mars. When Mark Watney is finally rescued on Sol 549, his astronaut buddies gather around him as Watney removes his helmet. The stench makes them step back. For those interested in the “gritty” realities of space survival you can’t get much better than The Martian.

935 JULY 20, 2014: Extreme Sun and Moon Distances Revealed: I have always been interested in eclipses of the sun and the moon and make it a point to discuss these phenomena with my classes in much greater detail than most astronomy teachers. My reasons are simple. They involve the precise alignment of the two most important astronomical bodies in the sky, the sun and the moon; but more importantly, they are strikingly beautiful events which seem to never repeat themselves in the exactly the same manner. So seeing one total lunar eclipse (moon hides in the Earth’s shadow) or one total solar eclipse (moon hides the sun) may not be enough to satisfy the artistic palette, but I try not to get too fanatical here. The curiosity of eclipses in our Earth—moon—sun system is the fact that the ratios of the sizes of the sun and the moon are inversely proportional to their distances from the Earth. Simply put, the sun is about 400 times the diameter of the moon, but the sun is also about 400 times more distant from Earth than the moon. This makes sun and moon appear virtually the same size at their average distances from our planet. The fact that both Earth and moon revolve around their respective bodies in oval-shaped orbits creates conditions where central solar eclipses do not have to be total. The center of the moon could pass in front of the center of the sun, but the moon could be too far from Earth, and therefore, too small in angular size to cover the sun completely. A ringed or annular eclipse would be the result. These changes in the angular diameter of the sun and the moon cannot be seen with the unaided eye, but they can be witnessed using the same camera-telescope combination with images taken when the sun and the moon are at their extreme near and far distances. I recently completed this multiyear project by photographing the sun on July 3 at its greatest distance from Earth. Compare the extreme sun-moon distances at the URL below. Click on “this week’s StarWatch.”

936 JULY 27, 2014: Meteor Season Upon Us: The summertime heralds the increase of meteor activity which coincides nicely with our desire to spend more time outdoors. I have lots of fond camping memories during these warmer months. My friends and I would specifically choose a dark location, often in New England, to view shooting stars. The evening hours before midnight were literally a hoot. A bright shooting star would flash without warning, and pockets of cheers and screams from observant campers would echo against the black dome of the star-filled sky. Gradually, as the hours ticked away, the campground hoopla would slowly fade, so that by 1 a.m., it was normally just my friends and I who were still watching. We were usually in silent competition to see who could observe the most meteors. The nights were always very dewy, so plastic covering our sleeping bags and air mattresses, as well as a ground tarp, were a must; and if we were imaging the sky, some type of battery operated, dew-busting heater around the lens was mandated. Chemical hand warmers left over from the winter months, now serve as lightweight, nonelectrical substitutes. Just remember to bring along rubber bands for their snug attachment. A tripod and a cable release or intervalometer are also necessary. Unfortunately, the biggest meteor shower of the summer, the Perseids, will be highly curtailed by a nearly full moon this year. The best nights are on August 11/12 and 12/13. The moon is full late on August 10; but still, don’t be discouraged. By the end of July, during new moon week, there are five minor streams that are active, in addition to the Perseids, which are just beginning to heat up. Early Perseids have a reputation for producing memorable fireballs. The Perseids are radiating from the NE, while the other meteors are spilling outward from the south. A clear, moonless night in a rural setting should yield hourly rates of at least 10-20 shooting stars after 1 a.m. Much success!

[July Star Map]

[July Moon Phase Calendar]