August skywatch: meteors, Mars and a blue moon

Get ready to stay up late and look up. August is packed with skywatch events that take place in the wee hours — and the skies are expected to clear this weekend, just in time for the opening act.

First up is the annual Perseid meteor shower, which runs from July to September. This year the celestial display peaks on Aug. 11 and 12.

This is one of the best-known meteor showers of the year — John Denver references the Perseids with the lyric, “I’ve seen it raining fire in the sky,” in his hit song, “Rocky Mountain High” — with the potential for up to 100 meteors per hour flashing across the sky. 

The meteor shower is the result of Earth passing through the debris field from comet 109P/Swift-Tuttle, which was independently discovered by Lewis Swift on July 16, 1862, and Horace Parnell Tuttle on July 19, 1862. It is a Halley-class comet, meaning that it orbits the sun between every 20 to 200 years. This comet makes its pass every 133 years, leaving behind a trail of icy debris ranging in size from a grain of sand to peas and even marbles.

Comet Swift-Tuttle is the largest object known to make repeated passes near Earth. Its nucleus is estimated to be approximately 16 miles across, roughly equal to the object that collided with Earth and wiped out the dinosaurs some 66 million years ago. Don’t fret, however; skywatch calculations have determined that its next closest pass will put it about a million miles from Earth — in the year 3044.

Perseid meteoroids are anywhere from 60 to 100 miles apart, even at the densest section of the river of comet debris. They enter Earth’s atmosphere as meteors at roughly 133,200 miles per hour. Almost none hit the ground, as most Perseids burn up in the atmosphere at heights above 50 miles. 

For the best viewing, Steven Bellavia of the Custer Institute and Observatory in Southold recommends waiting until the wee hours. “After midnight is ideal, as the waxing crescent moon will have set, and that is also when the ‘windshield’ — where you are on Earth, looking up — is facing the direction of our [rotation], which makes the meteors more visible than glancing blows from the sides.” 

The meteors will mostly appear to radiate from the constellation Perseus — hence the name — in the northwest sky near Cassiopea (aka the crooked W), but the wider the viewing field the more, will be visible, so be prepared to look in all directions.

Custer Institute and Observatory is open to the public every Saturday night, making it a good venue to observe the shower. Select state beaches will also be open late for stargazing. 

Later that week in the skywatch world, Mars will approach Jupiter in a close conjunction that culminates on Aug. 14 when the red planet will traverse the sky less than the width of a full moon from the gas giant. The planets will only appear to be close together from Earth’s vantage point, but in fact will remain more than 300 million miles apart.

With an unaided eye, Jupiter’s white light will contrast with Mars’ dimmer, redder hue. Jupiter’s moons will be visible through binoculars but the conjunction will be great for viewing with a telescope, as both planets can be seen in one frame. 

Last up for August skywatch, there is an “extra” full moon on Aug. 19 this year, the third of the season and thus known as a blue moon. Although it’s generally accepted that a blue moon refers to the second full moon in a single month, the more precise definition classifies it as the third of four full moons in the same season, which leads to a total of 13 for the year. And despite the popular phrase “once in a blue moon” signaling a rare or unlikely event, blue moons are fairly common in celestial terms, occurring every 2.7 years on average.