WHAT S UP? SEPTEMBER 2013

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1 WHAT S UP? SEPTEMBER 2013 Stars? What stars? The chances of rain subside somewhat in September which, hopefully, will mean the storm clouds will exit the area a little earlier in the evening and allow for some nighttime viewing. Some of the visible constellations are (starting towards the east and moving west): Pegasus, with its Great Square, is well positioned about 45 degrees above the horizon to the east. Andromeda, containing the Great Galaxy (M31), and Cassiopeia are further to the northeast. Cygnus and the Summer Triangle are still very close to overhead. Sagittarius has moved lower in the sky to the southwest. Ursa Major (the Big Dipper) has moved around to the north northwest and is less than 20 degrees from the horizon.. Hercules is still well positioned to the west about halfway between the zenith and the horizon. The Milky Way starts in the southwest, passes directly overhead and ends in the northeast, positioned for the best viewing of the summer. The Night Sky for Mid-Month at 10PM (Credit: Cartes du Ceil)

2 Here is the planetary roundup for September: Mercury will be in the Western sky during September, but will spend the entire month very close to the horizon after sunset, making it very difficult to see. Venus remains in the western sky but suffers from the same phenomenon as Mercury, keeping it lower to the horizon than normal. It will be much more visible, however, because (1) it is much brighter and (2) it is further from the Sun. The most notable event involving Venus this month is its close passage by the Moon on the 8 th. Mars has moved far enough from the Sun to be easily seen in the morning sky, but it doesn t rise until about 03:30 by mid-month. Jupiter rises about 2 hours earlier than Mars, but that rise time is still after midnight all month. Saturn is slowly moving closer to the Sun, but is still far enough away to be seen. It doesn t set until after 21:00. On the 20 th, Saturn will lie about 4 degrees north of Venus. Events for September: Date Sunday, the 1 st Thursday, the 5 th Sunday, the 8 th Monday, the 9 th Sunday, the 15 th Thursday, the 19 th Friday, the 20 th Sunday, the 22 nd Wednesday, the 25 th Friday, the 27 th Saturday, the 28 th Description Mars 6 N of the Moon New Moon Venus 0.4 N of the Moon (occultation) Saturn 2 N of the Moon Moon at perigee (will appear very large) Full Moon Venus 4 S of Saturn Autumnal Equinox (goodbye, Summer) Shadow transit (Callisto) on Jupiter Double shadow transit (Io, Europa) on Jupiter Jupiter 5 N of the Moon Occult-what? No, it has nothing to do with the supernatural. An occultation occurs when one body passes behind another. It can be a planet passing behind the Moon or a star passing behind the Moon or, rarely, a planet. An occultation may not be visible everywhere on Earth depending on the position of the two objects. An extreme example is when the further object just barely passes behind the edge of the nearer object this is called a grazing occultation. In the case of a star being occulted by the Moon, you may see the star blink on and off as the star passes behind the mountain peaks on the Moon. An extremely rare occultation occurred on the 13 th occulted by Venus. of October 1590 when Mars was

3 A Near-Miss for us, an Occultation for Others On the evening of September the 8 th, Venus will pass very close to a 3-1/2 day-old Moon. From our vantage point, the distance between the two will be about two degrees. However, in the southern hemisphere, Venus will pass behind, or be occulted by, the Moon (if you happen to be in Kiribati, French Polynesia, the Pitcairn Islands, southern South America or the Falkland Islands, check it out). The closest approach of about 4/10 ths of a degree, unfortunately, occurs during the afternoon for us when the planet is not visible. Venus passes very close to a waxing crescent Moon in September. Look near the horizon to the WSW to see it. (Credit: Sky Safari Pro)

4 Shadow Transits on Jupiter Most people have seen photos of solar eclipses where the Sun s shadow passes across Earth s surface, but the views are always from the perspective of the planet s surface. Did you ever wonder what it looks like to see that shadow from space? Well here s the chance to imagine it by looking at the phenomenon on another planet. Toward the end of this month, Jupiter will have two interesting events occurring on its surface: shadow transits. Shadow transits generated by the Galilean Satellites (Io, Europa, Ganymeade & Callisto the four brightest moons discovered by Galileo Galilei in the 1600 s) occur on Jupiter routinely, but these two transits are fairly rare. On September 25th, the shadow of Callisto (the Galilean Satellite furthest from Jupiter) will transit the planet. Callisto s orbit around Jupiter is such that its shadow doesn t transit Jupiter that often. In fact, the last time was in The transit will begin at approximately 03:15 MDT and will end about 05:25 MDT. The transit, as can be seen in the diagram below, will be in Jupiter s south polar region. Two days later, on September 27th, Io and Europa (the two closest Galilean Satellites) will have their shadows on Jupiter at the same time but very briefly. Europa s shadow will appear at 16:12 MDT (in the afternoon) and exit at 18:46. Io s shadow will appear at 18:45 and exit at 20:58, so the two shadows will be visible together for one minute! To see these two events will definitely take a telescope and the double shadow transit will be extremely difficult to see since it occurs basically right at sunset, meaning the sky will still be very bright. People on the East Coast will have a much better chance of seeing it. Callisto s shadow will pass across Jupiter on the 25th (Credit: Sky Safari Pro) Io s shadow will appear on Jupiter just as Europa s shadow departs. (Credit: Sky Safari Pro)

5 Focus On Sagittarius Look to the south southwest to see Sagittarius. (Credit: Sky Safari Pro) In September, the Milky Way rises out of the southwest, passes directly overhead and sets in the northeast. About 20 degrees above the southwest horizon and just to the left of the Milky Way sits Sagittarius, The Archer. The familiar asterism, The Teapot, has its spout spewing millions of steamy stars across the sky. Not only is Sagittarius an intriguing sight, it is also a signpost that points to the very center of our galaxy. As shown in the illustration above and the picture below, the hub of the Milky Way resides directly next to the Teapot s spout. In Alex Mellenger s wide-angle photo of the Milky Way, the hub is clearly visible. Sagittarius is Latin for The Archer and the Greeks said the constellation was a centaur combined with the archer Crotus. Crotus was a friend of the muses and a rather boisterous fellow. While listening to their music, Crotus would stomp his feet and clap loudly. The muses were so fond of his behavior that they had Crotus placed in the heavens. There are no fiercely bright stars in Sagittarius; most are 2 nd magnitude or dimmer, but the Teapot asterism provides the constellations notoriety. What Sagittarius lacks in stars, it makes up for in deep space objects. Fifteen of the 110 Messier objects reside within this constellation. M24 (shown in the illustration above only), is considered to be the densest part of the Milky Way. This area is an incredible view through binoculars.

6 M22 is a globular cluster that is easily visible through binoculars. This cluster is also the closest one to our solar system, being only 10,000 light years away. The cluster is estimated to contain a half million stars in an area only 97 light years across. That is incredibly dense considering our nearest star is over 4 light years away. Two other Messier objects that are visible very near the Teapot s spout are M8 (the Lagoon Nebula) and M20 (the Trifid Nebula). M8, a cloud of glowing gas (similar to the Orion Nebula) is about 5200 light years away and spans an area three times that of the Full Moon, which makes its actual size about the same as M22: 100 light years across. M8 can barely be made out with the naked eye, but is better viewed through binoculars or a small telescope. M20 is very close to M8 and contains two sections. One glows with red light that is emitted by the gas. The other section is blue in color, which represents reflected light. The Triffid Nebula is just slightly smaller in diameter than the Moon. M20 can be viewed through binoculars, but will appear as a hazy ball. When viewed though a small telescope, more detail can be seen. In this picture, the red cross marks the center of the galaxy. The bulge of the galaxy s central hub is clearly seen. (Credit: Axel Mellenger)

7 M22 is located at the top of Sagittarius head. (Credit: Jim Misti) M8 (The Lagoon Nebula) is in the lower left part of the picture and M20 (The Trifid Nebula) is in the upper right part of the picture. These are located near the upper part of Sagittarius bow. (Credit: Robert Gendler)