Star Trak: August 2016
FOR IMMEDIATE RELEASE
BLOOMINGTON, Ind. -- The annual Perseid meteor shower, which will peak on the night of Aug. 11-12, is one of the most popular every year because it happens on warm summer nights, when gazing at the starry sky is always enjoyable. This year the moon will set at 1 a.m. local daylight time at the shower’s peak for mid-northern observers, so viewing conditions will be ideal for three or four hours in a clear, dark sky. There may be as many as 90 meteors per hour, some with smoke trails that will last several seconds after the meteor has vanished.
The Perseids will be visible for most of August, though there will be fewer meteors to see the farther from the peak date you watch. If the peak is hidden by clouds, try looking for meteors again as soon as the night sky is clear. To minimize the effect of local light pollution, which can obscure as many as half of the meteors, try to avoid artificial lights. Face east if you have a clear view in that direction, and look about halfway up the sky from the horizon. You won't need binoculars or a telescope because the meteors move much too fast for those devices. The chances of seeing a fireball will be greatest near dawn, when Earth will be moving head-on into the meteor stream.
The Perseids may appear anywhere in the sky, but they will seem to originate from a point called the radiant in the constellation Perseus, which gives these “shooting stars” their name. The higher the radiant is above the northeastern horizon, the more meteors will be visible. Perseus is just north of the W-shaped constellation Cassiopeia in the Milky Way, with the bright star Capella and the Pleiades star cluster below it. Meteors near the radiant will have short trails because we see them nearly straight on, while those far from the radiant will look longer because they are seen from the side.
Most meteor showers happen when Earth crosses the orbit of a comet; the Perseids come from Comet Swift Tuttle. The meteors are caused by particles released from the comet’s nucleus and left behind in space. As Earth plows through this stream of debris, ranging in size from sand grains to pebbles, each particle slams into our atmosphere at a speed of more than 30 miles per second and burns up almost instantly from friction with air molecules. The resulting heat momentarily creates a streak of glowing air that we see as a meteor. All of this happens about 60 miles above the ground, regardless of how close some meteors may appear.
Planets
As darkness falls during the first few days of August, Jupiter, Mercury and Venus -- in that order, from upper left, the south, to lower right -- will form a line very low in the western sky. Use binoculars, because Venus will be only 4 degrees high just 20 minutes after sunset as seen from mid-northern latitudes. It will set 45 minutes after the sun. Mercury will set about 15 minutes later, and Jupiter will follow in another 45 minutes. The three planets will be joined by the bright white star Regulus, which will be close to Venus.
These four bright objects will form various combinations as they draw closer and pass each other during the month. The best conjunction for mid-northern observers will happen on Aug. 27, when Venus and Jupiter will come as close as 0.1 degree 45 minutes after sunset. A clear view of the western horizon will be needed to see it. Those watching the pair of planets with the naked eye may see their lights blended together.
On this same evening, the trio of Venus, Jupiter and Mercury will fit within their smallest circle of sky, just over 5 degrees in diameter.
Mars and Saturn will combine with the bright red-orange star Antares -- the brightest star in the constellation Scorpius, almost the same color as Mars -- in a beautiful show during August that will be much higher in the sky and easier to see. The two planets will be well up in the south-southwest a half hour after sunset. Look for them with a telescope at dusk before they sink lower. On Aug. 23 and 24, Mars will pass between Saturn and Antares.
Saturn’s biggest moon, Titan, is easy to see with any telescope. It will be due north of Saturn on Aug. 8 and 24 and due south on Aug. 15 and 31. The planet’s famous rings will tilt 26 degrees to our line of sight.
Light pollution
If you look at the constellation Cassiopeia in the northeast on a clear summer night and can't see the Milky Way sprawling high across the sky from the northern to the southern horizon, it means your sky has significant light pollution, which is the case for about two-thirds of the world's population. This dimming of the night sky is caused by excessive artificial lighting, much of which is wasted. See the International Dark-Sky Association website for more information.
Moon phases
The moon will be new on Aug. 2, at first quarter on Aug. 10, full on Aug. 18 and at third quarter on Aug. 25.
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Hal Kibbey
- Office 812-336-1333
- hkibbey@indiana.edu