Mars is still the star of the night show this month; but now's also a good time to catch your final glimpse of summer, and keep an eye out for an autumn phenomenon while you're at it.
The summer sign is called the Summer Triangle, says Alex Mack of the University of Toledo's Ritter Planetarium. And you don't need a telescope, or a particularly dark sky, to see it.
“It's even visible in downtown Toledo,'' Mr. Mack said. That's how prominent these three stars appear.
They're actually bright stars in three separate constellations, arranged as a large right triangle directly overhead. Patterns that take in more than one constellation, or include only a portion of a larger constellation, are called asterisms. The Big Dipper may be the most familiar of these. It's part of Ursa Major, the great bear.
The Summer Triangle is a pretty big feature. If you hold your fist at arms length, you can probably fit two or three fists into the triangle.
The triangle's corners are lit by the stars Deneb,Vega, and Altair, in the the constellation Cygnus, the swan; Lyra, the lyre, and; Aquila, the eagle, respectively.
Vega is the brightest of the three stars, and the closest to being directly overhead. It's about 25 light years away,
Deneb will be the faintest, and the northernmost star. Don't let its modest glow fool you. This is a supergiant star, nearly 100 times the size of the sun, and 70,000 times brighter. But it's so far away - 3,200 light years - it's only the 20th brightest in the night sky.
Altair is the southernmost star. It's 150 percent larger than the sun, and 11 times brighter, but it's about 16 light years away. Consequently, it's the 12th brightest star in the sky. This star spins so fast - with a rotational speed of 150 miles per second -
that it looks smooshed through a telescope.
As summer fades, the triangle will move toward the western horizon. By the end of this month, it will be about a third of the way to the horizon.
As the Summer Triangle sinks, the chance of seeing the Northern Lights increases. Geomagnetic storms cause auroras. And autumn has twice as many of these as the rest of the year.
Auroras occur when solar winds strum Earth's magnetic field. The solar winds are actually explosions on the sun's surface near sunspots. When these gusts, also known as coronal mass ejections, erupt, they blow into a layer of electrons and protons that surround the Earth called the magnetosphere. Atomic particles knocked loose by this jolt cascade to Earth, making the atmosphere glow with dazzling and weird lights.
Also this month, if you're lucky, you may catch a glimpse of the planet Mercury, Mr. Mack says. Mercury is so close to the sun, it's usually overwhelmed by its light. But on Sept. 26, it will be as far from the sun as it's going to get.
To get a good look, go outside about 6:30 a.m. Mercury should be low in the Eastern sky.
Mars, by the way, will be on display all month, very slowly fading from its Aug. 27 peak.
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