Sky-Watching Activities for September and October 2012

by Robert C. Victor

Evening sky gazing

In early September, two contrastingly colored stars are the brightest points of light in the deepening twilight one hour after sunset. Both of zero magnitude, they are blue-white Vega nearly overhead, and golden-orange Arcturus nearly due west about one-third of the way from horizon to overhead. Stars of lesser brightness, but still of first magnitude, are Altair to the SSE of Vega and Deneb to the ENE, completing the Summer Triangle with Vega; and reddish Antares, low in the south-southwest. Have your students keep track of these stars in twilight in coming months, and they’ll witness the effects of the Earth’s annual revolution around the Sun.

With Mars and the Curiosity Rover now in the news after the spectacular landing in August, it might be fun for students to locate Mars while it’s still visible in the evenings until it sinks into the twilight glow in February. In the first week of September, Mars is low in SW to WSW, but still easily seen with aided eye, some 30 degrees lower right of Antares. Mars will appear two or three degrees lower-right of the waxing crescent moon on Sept. 19, and about six or seven degrees lower-right of the crescent on Oct. 18. On the latter evening, Antares will appear about seven degrees below the moon. During Oct. 18-22, Mars stays within four degrees of Antares as the planet passes north of the star. Ask students to look up the meaning of this star’s name.

Image courtesy of Abrams Planetarium. Subscriptions to the sky calendar ar  $11.00 per year, starting anytime, from Sky Calendar, Abrams Planetarium, Michigan State University, 755 Science Rd, East Lansing, MI 48824 or online.

Saturn is still visible in evening twilight in September, but is easier to spot earlier in the month, when it sets in a darker sky. On Sept. 4, look 12 degrees lower right of Mars; on Oct. 1, look about 27 degrees.

Daytime Moonwatch

Observing the moon at same time daily is best done at a time of day when the Sun is low in the sky. At this time of year while we’re on daylight saving time, the Sun is still rather high when the typical school day ends in mid-afternoon. Consequently, it’s impossible to observe the full and nearly full phases of the moon when the Sun is this high in the sky.

So, in early fall we recommend you schedule a daytime moonwatch in the morning as the first activity of the school day or during the playground time before classes start. Have the students record the shape or phase of the moon and its location in the sky, perhaps using foreground buildings and trees as a reference. It’s a good idea to have students make their observations from the same location each day. At the start of the 2012-2013 school year, the moon starts out very visible! On the day after Labor Day at 9 a.m. (the time many local elementary schools start their classes) the moon will be some 20 degrees above the western horizon and in gibbous phase, nearly 85 percent illuminated. If you observe the moon before 9 a.m. you’ll find it even higher in the sky. The Earth’s rotation will cause the moon to set, so don’t wait until lunchtime to look for the moon that day!

Returning each day to record their observations, the students may notice changes in the phase, or apparent shape of the illuminated area of the moon, as well as its position in the sky. (Try not to “spill the beans” to your students, even though I’m doing so for you here.) By Friday, Sept. 7, the moon will appear some 60 percent full, and will between W and WSW, higher in the sky, some 50 degrees above the horizon. The morning moon moves, on average, about 12 degrees closer to the Sun each 24 hours. On Saturday, Sept. 8 (for weekend homework?) students will find the moon half full at 9 a.m., some 60 degrees up in WSW. That day, the moon will be found 90 degrees or one-quarter circle to the west of the Sun, as it enters the Last Quarter of its cycle of phases which will end when the moon passes nearly between Earth and Sun on Saturday, Sept. 15. On its way there, the moon will appear as a fat crescent some 40 percent full high in the SW at 9 a.m. on Sunday morning, Sept. 9.

Meet the students each morning Sept. 10-14 to follow the waning crescent. By Wednesday Sept. 12 it should still be easy in a clear sky, although it has slimmed to 14 percent full and has moved to within 45 degrees of the Sun. On Thursday the 13th, the moon is just seven percent Full and only 30 degrees from the Sun. Are your students up for the challenge? Kudos for all who catch the three percent crescent on Friday the 14th, just 19 degrees from the Sun. Note that if your students miss the daytime morning observing window for Sept. 4-14, you can schedule one for October 2-14 instead.

For those with access to a telescope, you can provide students with close-up views of lunar craters and other features. This usually works best around sunrise or sunset, or at night, when the sky brightness won’t drown out the details. However, by inserting a single polarizing filter into the telescope’s low-power eyepiece, you can often improve the image contrast markedly. Here’s how it works: In a clear blue sky, sunlight scattered from the parts of the sky around 90 degrees from the Sun is strongly polarized. So, thread a single polarizing filter into the eyepiece, aim the scope at the moon when it is within a couple of days of half full (Last Quarter in the morning sky, or First Quarter phase in the afternoon sky), and, while you are looking at the moon, turn the eyepiece until the darkest blue sky is achieved. You and your students will be amazed at the lunar details to be seen in the daytime! Polarizing filters fitting threaded eyepieces can be obtained from Orion Telescopes and Binoculars, at telescope.com. The filters come in pairs, but install just one of them into your eyepiece.

You can observe the polarization of sky light by putting on a regular pair of polarizing sunglasses. Face a patch of blue sky 90 degrees from the Sun. With the glasses on, try tilting the top of your head until it is directly exposed to the Sun, and then compare the brightness of the sky to when you aim your “ear-axis” toward the Sun.

Get your students outdoors — on dark mornings!

With daylight saving time still in effect during the first two months of the school year, dark skies can be observed in the morning without getting out of bed outrageously early. In Fall 2012, there is much worthwhile to be seen. When the moon is visible before sunrise (Sept. 4-14, Sept. 29-Oct. 13, and Oct. 29-Nov. 12 in 2012), the four brightest objects in the night sky are all visible – the moon, Venus, Jupiter, and the star Sirius – along with the bright winter constellations of Orion the Hunter, Taurus the Bull, and many others.

In September through December 2012, we’ll see spectacular conjunctions of the waning crescent moon and Venus before dawn on Sept. 12, Oct. 12, Nov. 11, and Dec. 11. Jupiter will appear near the moon on the mornings of Sept. 8, Oct. 5 and 6, Nov. 1 and 2, and the evenings of Nov. 1, 28, and Dec. 25.

Before dawn in autumn, the three most brilliant “stars,” Venus, Jupiter, and the Dog Star, Sirius, dominate the sky. While daylight saving time is still in effect until early November, this is a good time of year to schedule sky-watching sessions for your students at a reasonable hour, or to encourage them to observe on their own with their families, beginning in darkness 1-1/2 to 2 hours before sunrise. Later this autumn, Saturn will emerge in the morning twilight to the lower left of Venus and the star Spica by the second week of November. Venus will pass only 0.2 degree from the star Regulus on October 3, within four degrees north of Spica on Nov. 17, and will appear less than a degree from Saturn on the mornings of Nov. 26 and 27. These close pairings will be very interesting to follow for several consecutive mornings around those dates. Mercury will have a fine morning twilight apparition low in ESE to SE sky during Nov. 24-Dec. 28. Look for our solar system’s innermost planet to the lower left of Venus, within 10 degrees Nov. 29-Dec. 28, and within 6.5 degrees Dec. 5-12. During Mercury’s morning apparition, four of the five naked-eye planets will be visible simultaneously!

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Written by Robert Victor

Robert C. Victor was Staff Astronomer at Abrams Planetarium, Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs, CA.