August Is Going to Be a Busy Month in the Heavens

From a Washington Post story by Geoff Chester headlined “Blue Moon, Perseid meteor shower highlight busy August in the heavens”:

August is going to be a busy month in the heavens. We’ll have two full moons, the year’s best meteor shower, and, although we will lose sight of two planets, two more swing into view.

Twice in a month, or once in a blue moon?

The month’s first full moon happens Tuesday at 2:32 p.m. Eastern time. August’s full moon is traditionally known as the Sturgeon Moon here in North America, because the continent’s largest freshwater fish are beginning their spawning season. Other names include the Grain Moon and Corn Moon.

But this month, there’s a bonus moon.

The second full moon will occur Aug. 30 at 9:26 p.m. Eastern time and is one of two types of “blue moons.” This term applies to either the second full moon in a calendar month (as we have this year) or the third full moon to occur in an astronomical season (between equinoxes and solstices) that has four full moons. This second type of blue moon will occur on Aug. 19 next year.

Both of this month’s full moons also happen to occur close to the times of the moon’s closest pass to Earth in its orbit — known as perigee. Some people like to refer to perigee moons as “supermoons.” These moons appear about 8 percent bigger and 16 percent brighter than an average moon.

Another obscure astronomical event

Aug. 1 was once a special day in pre-Christian Gaelic culture, one of the four “cross-quarter” days that marked the midpoints of the astronomical seasons. Known as Lughnasadh, it was widely observed in Scotland, Ireland, Wales and the Isle of Man as the first of three harvest festivals. When Christianity arrived in these regions, the day became the feast day of St. Peter in Chains.

It subsequently evolved into “Lammas,” or “Loaf Mass.” On this day, it is traditional to bring the first loaf of bread made from the first crop of the season to the church for all to share. Unlike the other cross-quarter days that we know as Groundhog Day, May Day and Halloween, Lammas isn’t widely observed in the United States, but it is still popular in Britain and marks the “traditional” start of summer holidays in many parts of Europe.

Prepare for the Perseids

Go out on almost any moonless night in August and you are bound to see a few “shooting stars.” Go out on the night of Aug. 12-13 and you will see lots of them. This is the night when the annual Perseid meteor shower reaches its peak, and a single observer at a dark-sky location can expect to see between 50 to 75 meteors in an hour.

The Perseids are perhaps the year’s most consistent meteor shower, and they occur under nearly ideal circumstances this year. The crescent moon won’t rise until well into the early morning hours, and the mild nights are perfect for stretching out on a comfortable beach chair and looking skyward.

The Perseids originate from tiny particles of rocky material that sputter from the nucleus of a comet, they then spread out along the comet’s orbital path. Each year, the Earth plows into this material on the same date, producing the shower. Records of the shower date back well over 2,000 years.

The parent comet, known as 109P/Swift-Tuttle, orbits the Sun about every 133 years and was discovered in 1862 by Lewis Swift and Horace P. Tuttle, the latter who would later become an astronomer at the U.S. Naval Observatory.

The Perseids are so named because the point in the sky from which they appear to originate is near the constellation Perseus, which rises in the northeastern part of the sky in the late evening. Viewing the meteors requires nothing more than your eyes and a dark site. I like to use a beach chair and point my feet to the northeast. This gives me a nice view of most of the sky.

Perseid meteors move swiftly, flashing by in mere instants. Occasionally, an exceptionally bright “fireball” may take you by surprise, often fragmenting and leaving a luminous train in its wake. While they often appear to be very close to you, they are over 100 miles away. The typical Perseid meteoroid is not much bigger than a grain of sand; the larger fireballs are about the size of a ping-pong ball. They hit Earth’s atmosphere at tremendous speeds, 35 to 40 miles per second, and ionize the air around them, producing the flash of light.

Saturn returns, and Jupiter waits in the wings

We had bid farewell to Venus in July, and Mars is now becoming difficult to spot in bright evening twilight.

Fortunately, Saturn comes in the nick of time for us to view in our telescopes. As August opens, the ringed planet rises at about 9:30 p.m., and by midnight you should have little trouble spotting its yellow hue in the southeastern sky. This part of the heavens is taken up by a number of very obscure, dim constellations, so Saturn will definitely stand out.

Almost any small telescope will reveal the planet’s enigmatic rings, and a good six-inch instrument will show the planet surrounded by several of its icy moons. The rings themselves are made up of trillions of small ice particles that are herded by the gravity of the planet’s inner moons. While they span an expanse of about two-thirds the distance between the Earth and the moon, they are incredibly thin, perhaps a few hundred feet at most.

Saturn reaches opposition, when Earth lies directly between it and the Sun, on Aug. 27. On that date, it rises at sunset and sets at the following sunrise. It will be well-placed in the evening sky through the end of the year.

Giant Jupiter rises just after midnight at the beginning of the month, and as September opens it will be prominently placed high in the eastern sky by midnight.

Jupiter is big, brash and bright as celestial objects go, and it offers something for anyone with a little optical aid. A steadily held pair of binoculars is enough to show the four moons first described by Galileo in 1610. They change their configurations from night to night, so they are always fun to watch.

Small telescopes show the equatorial cloud belts on the Jovian surface, and a good 4-inch instrument will show the famous Great Red Spot, thought to be a gigantic storm in Jupiter’s atmosphere. The Spot may look small in the eyepiece, but its surface area is about the same as that of the entire Earth.

Geoff Chester is an astronomer who has worked at the U.S. Naval Observatory since 1997.