StarWatch: Moravian College Astronomy

StarWatch for the greater Lehigh Valley

JULY 2015

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:

985 JULY 5, 2015: New Horizons for Pluto and Clyde: When New Horizons was launched in 2005, headed towards a July 14, 2015 rendezvous with enigmatic Pluto, the God of the Underworld was still a planet. A year later, Pluto was demoted by the International Astronomical Union when it formally defined that a planet had to be round, orbit the sun, not be a moon of another planet, and clear its own space. Pluto, which is 1470 miles in diameter, was dropped to dwarf planet status because its small size and its mass did not give it enough gravity to clear its orbital path of debris. Still, it was not all bad news for Pluto, which was elevated to the most prestigious of a new grouping of cold, outer solar system objects which danced beyond Neptune, known as Plutoids or more commonly, Trans-Neptunian Objects (TNOs). Four of these, Eris (most massive), Pluto, Makemake, and Haumea are also recognized as dwarf planets, but over 1500 other TNOs have been discovered to date. Evidenced in images being returned as New Horizons approaches Pluto is a varying landscape of blobs and blotches, but it is still too early to decipher specifics. Charon, Pluto’s largest of five moons, about 750 miles in diameter, has an unexpectedly dark north pole. Will Pluto have nitrogen geysers like Neptune’s largest active moon, Triton, thought to be a captured TNO, or will Pluto’s yet unseen craters and topography be worn down by eons of tenuous winds created by the sublimation (ice to gas without a liquid interface) and refreezing of methane, nitrogen, and carbon dioxide gases during Pluto’s 248-year orbital period and seasonal cycle. One thing is certain, Clyde Tombaugh, Pluto’s discoverer (1930), will have the ride of his afterlife as New Horizons swings past his planet. Stored in this piano-sized spacecraft is a small urn containing some of Clyde’s cremated remains. It is a wonderful tribute to the man with unparalleled perseverance who discovered the wanna-be planet that couldn’t.

986 JULY 12, 2015: Last Tango: Venus, Jupiter, and the Moon: This week marks that last chance you’ll get until October to view Venus and Jupiter in close proximity. They are now about five degrees apart, about 15 times farther away than at their closest on June 30. It’s been a tough go for East Coast observers because of clouds. Be at your observing location with an unobstructed western horizon about 35 minutes after sundown. Dazzling Venus, about 12 times brighter than Jupiter, will be to the left. Jupiter will still be the second brightest object in the sky until the crescent moon enters the scene on Saturday, July 18, one degree below Venus. Here is a real test of visual acuity. Although the total luminescence of the moon will be about 400 times brighter than Venus, the moon’s brilliance is mainly due to its large size. Venus and Jupiter have much greater surface brightnesses than the moon. My prediction is that you’ll easily catch Venus and Jupiter in the dimming twilight, but you may need binoculars to reveal the moon before it sets. All three objects, including the alpha star of Leo the Lion, Regulus, should fit into the field of view of average binoculars—pretty impressive indeed. If July 18 is a washout, the moon will have pulled away significantly from Venus by the 19th, but the scene will still be very beautiful to witness. Because the moon will be higher in the sky and brighter, all three objects—the moon, Venus, and Jupiter should easily become visible to the unaided eye if sky conditions are clear enough. The key again is having an unhindered western horizon. By 9:30 p.m. anytime during July, you can check up on Saturn, due south about one-third of the way up between the horizon and the zenith. Don’t forget about New Horizons which passes Pluto on Tuesday, July 14. Stay tuned for some great images of the Underworld God and its primary moon Charon. Incidentally, dwarf planet Pluto is currently visible in the star pattern of Sagittarius through large telescopes about 45 degrees to the east of Saturn.

987 JULY 19, 2015: Pluto: A New World to Explore: New Horizons made it past Pluto and its five satellites without incident on July 14, and it is now moving towards an encounter, in approximately four years, with another Kuiper Belt object. The slow data transfer from the spacecraft has kept images to a minimum, and astronomers on tiptoes for days. At the time this article was written, July 15, I was itching to make some initial guesses from the best photos received up until that time. See the images posted on “this week’s StarWatch” at astronomy.org. Although Pluto basically orbits the sun on its side, and New Horizons punched through the Pluto system perpendicular to the orbits of its moons, I am labeling the pictures in a traditional fashion, up/down/left/right, as north/south/west/east to keep some sanity to my thoughts. The first aspect that struck me was the diversity of landscapes and that these are probably a function of internal and external changes occurring on and in Pluto. The lighter northern hemisphere is dotted with a myriad of craters, but they have been well worn over eons of time, maybe by a once thicker atmosphere or perhaps some melting process that comes to life as the dwarf planet gets nearer to the sun every 248 years. The southern hemisphere is darker, a sign that the terrain has been modified by external processes for a long period of time. As terrain ages, it picks up small bits and pieces of debris along the way darkening its surface. Yet in the southern hemisphere, there is this huge, worn, white impact feature dubbed unofficially as “the heart” which appears relatively featureless with large outflows to the east and to the south. Nitrogen geysers might be found there with tenuous winds moving some of that material away from the site. In addition, the southern hemisphere shows some recent cratering, new mountains, and what looks like several rift (fault) valleys. Whether I’m right or wrong, Pluto represents a whole new world which will be fun to explore. Stay tuned!

988 JULY 26, 2015: Blue, Blue Moon: An unusual full moon occurs this coming Friday, July 31. If you watch Luna rise about the time of sundown, besides noticing its larger size called the moon illusion, it will also be blue. Yes, this Friday is the blue moon, but don’t expect it to have a bluish tint or pine away at some unrequited love. It is just a synonym for the second full moon occurring during the course of a month, but it does fit the older “once in a blue moon” phrase because such moons are relatively rare. The first time I wrote about the blue moon (January 1999), I was in for a real shock. I had been using the standard astronomical definition for over a decade, but when I went to check the meaning in one of my 60 single subject books on the moon in my personal library, only one text referenced a “blue moon,” and that was when the moon actually appeared blue as it rose through ultra fine dust after a volcanic eruption in Indonesia. I was in a panic. There was a deadline to meet, I had a really great idea, and I had no way to prove it valid. Coincidentally, the same conundrum was occurring with the editors of Sky and Telescope, but they managed to solve the problem which the magazine incidentally had created. The 1937 edition of the Maine Farmer’s Almanac was the source, and it referred to the blue moon as the third full moon in a three month cycle of four full moons. Each month’s full moon had a seasonal biblical association, so when four full moons occurred in the space of three months, their calendar went out of sync. The third full moon in that series became known as the blue moon to keep the cycle in step with the year. The present-day usage occurred in a 1946 S&T article and then in a 1980 Public Radio broadcast. By 1988 the new blue moon definition was firmly fixed in the lexicon. Ask Siri, as I prompted Charbel Abi-Zeid, one of my tech-friendly astronomy students, to do on his iPhone. To my surprise, she nailed both the old and new definitions. Got to love technology… Happy Blue Moon!

[July Star Map]

[July Moon Phase Calendar]