StarWatch: Moravian College Astronomy

SEPTEMBER 2008

SEPTEMBER STAR MAP | STARWATCH INDEX | MOON PHASE CALENDAR

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Current Moon Phase

[Wildlife in Pennsylvania]

The perils of observing in Potter County, north central Pennsylvania, are great! Here are some of creatures that I had to fight off in just one night of stargazing. Gary A. Becker composite image from Carter Camp, PA with eyes supplied from a postcard marketed by Modern-Ad, Butler, PA...

629 SEPTEMBER 7, 2008: Red at Night, Volcanic Delight!: Here in eastern Pennsylvania, there were an extraordinary number of clear, cool days between the middle and end of August. In fact, I was able to photograph the moon on 11 consecutive nights from its full phase on August 17 through a 15 percent sunlit, waning crescent moon on the 27th. Those images were posted along with the August StarWatch articles which can be found at the URL below. On one of the clearest evenings during this period, the sun set against a cloudless, turquoise sky while I was doing some digging in the backyard. As the lighting became more subdued, I suddenly realized that the ground I was shoveling had taken on a coppery hue. I looked up to witness an orangey sky and a landscape bathed in surreal saffron. There was almost no structure in the coloration above, just a milky orange mist that had engulfed about half of the heavens. I stopped working and walked around my wooded property to get different vantage points. My conclusion was that maybe the day was not as clear as I had envisioned it. Unfortunately, rather then doing a quick hand scrub and grabbing my camera, I continued working. Recently, I have found that other sky watchers have been reporting ruddier sunsets too, and there seems to be an explanation. Three volcanoes in Alaska’s Aleutian chain, Kasatochi, Cleveland, and Okmok, have been active, ejecting fine particulate material (dust) and sulfur dioxide into the stratosphere. These are not Pinatubo (1991) or Mt. St. Helens (1980) type eruptions, but they have resulted in a heightened effectiveness of the atmosphere to scatter (filter) the blues and greens from the light of the sun. The results have created more vibrant sunsets across the US. So keep your camera handy for the next several months because we could be in for a number of sunset treats.

630 SEPTEMBER 14, 2008: Here Comes Venus: I noticed it just the other week on a very clear evening. About 20 minutes after sunset, Venus, the evening star, made a brief appearance in the west before Earth’s rotation carried it below the horizon. Venus has been in the western sky for over two months, but it has been lost in the sun’s glare. That’s because at this time of the year the plane of the solar system, along which all of the planets hug, is tilted at a very shallow angle to the horizon. Although Venus has moved a substantial distance away from the sun in the last 75 days, it has not gained much altitude, and therefore, it still sets shortly after sundown. Now is the time to start putting Venus in your sights because viewing conditions will be improving as we head towards the end of the year. Venus will be placed higher in sky, and, be therefore easier to spot. The European Space Agency has also had its eye on Venus through its Venus Express spacecraft orbiting our sister planet for over three Venusian rotations. Keep in mind that it requires Venus 243 days to complete one spin on its axis. Its primary focus has been to study Venus’s atmosphere and its interaction with the solar environment, and it has come up with a number of confirmations and surprises. We now know that lightning definitely exits in Venus’s blistering, hot clouds which are composed almost entirely of sulfuric acid. Venus’s upper atmosphere is also continuously being stripped away by plasma—charged particles coming from the sun, and this raises the question about what is replenishing its atmosphere. Volcanism seems to be the obvious answer, and evidence of active lava flows is now being sought. Finally, vortices have been discovered at both Venusian poles where its carbon dioxide atmosphere seems to plunge downward towards the surface. Venus is one nasty sister planet!

631 SEPTEMBER 21, 2008: Autumn Gloom: That moment has come when all fun loving, beach-going, summer people must pay heed to the fact that the good times are nearly over. On Monday the 22nd at 11:44 a.m. EDT, the sun crosses the equator at approximately 56 degrees west longitude and continues its long descent into winter’s darkness for the northern hemisphere. On September 22, the length of day and night will be equal. If by this time you haven’t figured out that I’m just a summer kind of a guy, then let me say it even more plainly. “I hate winter, unless we have a snow day.” Despite my gloominess over the colder weather that lies ahead, the few weeks surrounding the equinoxes, both autumnal and vernal, offer the best opportunity to witness some of the fastest changes that can take place in the heavens. By October 5, two weeks after the equinox, the sun will be over five degree lower at noon and the sunlit day will be shorter by 35 minutes for people living at 40 degrees north latitude. The effects are more pronounced northward and less noticeable, southward of that location. One positive aspect of the autumn months is the seasonal lag in temperatures. During the spring and summer, the northern hemisphere absorbs more energy than it radiates back into space. Temperatures along the East Coast reach their yearly maximums around the third week in July which causes the effects of summer to spill over well into fall. The big chill really does not happen until sometime in November. Halloween can still be pretty balmy, but by Thanksgiving those pleasantly warm Indian summer days are gone and won’t be returning until late April or early May. At least I’m not on the arctic plains of Mars which is also headed towards autumn. Highs recorded by the Phoenix lander are averaging -30 degrees F. and lows one hundred degrees colder. Now that is really frigid!

632 SEPTEMBER 28, 2008: The Heavenly Dance: One of the greatest joys of being an urban astronomer is to watch the planets and moon play in the twilight. October will offer some enjoyable dusk lunar and planetary vistas as well as the opportunity to watch the moon complete its full cycle of phases during one of clearest months of the year. The new moon passes the sun on September 29 and lies about five degrees, or one clenched fist held at arm’s length, below Venus two nights later on October 1. In order to witness this event, your western horizon will have to be unobscured and flawlessly clear. Use binoculars to spot Venus, about one field of view above the WSW horizon 30 minutes after sundown. That should be no problem. The difficult observation will be the thin, slivery moon hugging the horizon below Venus. October 2 finds the moon and Venus at the same elevation and visible together in a darker sky about 40 minutes after sundown. By October 3, the waxing crescent (growing, horned) moon will be easily visible along with Venus in the SW, 45 minutes after sunset. The following evening, the moon stands squarely between Venus and another very bright luminary in the south, Jupiter. Within two days on October 6, the moon has closed on Jupiter and lies just below and to its right, a fine binocular sight especially as twilight deepens. On October 7, the first quarter moon, half on—half off—light to the right, is even with Jupiter, but to its left. After October 7 the moon continues to wax or grow, but it ventures into the fall sky along a pathway which is devoid of bright stars. It is full on the 14th and moves into the morning, setting after sunrise. If you are an early riser, you’ll still be able to follow the moon when you wake, first in the west, then the south, and finally in the east. You’re now witnessing the heavenly dance, and it is enjoyable.