A pair of planets in the west; A great triangle in the east
One of the best shows of the year over Butler is this week in the evening twilight in the western sky. The bright planets Jupiter and Venus are in a tight celestial embrace this weekend but will get even closer this week.
If you’re even a casual observer of the night sky, I know you’ve noticed that extremely bright “star” popping out in the western twilight this spring. That’s Venus, the cloud-covered great oven of our solar system. It’s so bright because it’s relatively close to Earth, and its cloud cover bounces a ton of sunlight at us.
Just to the upper left of Venus is the next brightest “star,” Jupiter, which is not nearly as bright as Venus but will definitely get your attention. All spring long, Venus and Jupiter have been playing a gradual version of celestial chicken, driving toward each other. They won’t collide, but this Tuesday night they’ll pass each other, separated by only a degree and a half, about the width of two of your fingers held at arm’s length. After this Tuesday the planets go their separate ways.
Of course, Venus and Jupiter are nowhere close to each other physically, but appear nearly in the same line of sight. Venus is a little over 111 million miles from Earth and Jupiter’s over 560 million miles away. Close conjunctions like this happen on a regular basis because all the planets in the solar system — including our Earth — all orbit the sun in nearly the same plane, traveling at their respective speeds around our home star.
The cool thing is that for most of this week, you can get both planets in the same field of view with a pair of binoculars or a small telescope. What’s not so cool is that because Jupiter is so far away and Venus has complete cloud cover, you’re not going to see much detail. They’ll appear fuzzy because they’re both so close to the blurring effect of Earth’s thicker atmosphere near the horizon.
Meanwhile, in the eastern evening, the Summer Triangle is on the rise. It’s not an official constellation but rather what stargazers refer to as an asterism that really helps you find your way in the night sky. It’s one of the biggest asterisms in the sky.
Face the evening eastern sky and look up for the three brightest stars you can see. That’s it! Those three stars are at the corners of the Summer Triangle. Each of the stars is the brightest in its own constellation, so you have a way of locating three different constellations straight away.
The brightest and highest star in the Summer Triangle is Vega. It’s the second brightest star in the summer evening sky and also a historic star. In the early ’80s, it was discovered that Vega has a “dusty” ring, thought to be the start of a developing solar system. Vega, with a planetary system was featured in the movie “Contact” starring Jodie Foster.
Vega is 26 light-years away from Earth, with 1 light-year equaling nearly 6 trillion miles. A light-year is defined as the distance light travels in a year, meaning the light we see from Vega tonight left that luminary at the turn of this present century.
As bright as Vega is, it’s the brightest star in the puny little constellation Lyra the Lyre (pronounced liar, honestly). A lyre is a type of small harp, and I’m unsure how the constellation should look like a harp. All there is to Lyra is Vega and a small parallelogram of fainter stars to the lower right.
The next brightest star you see to the lower left of Vega is Deneb, on the lower left corner of the Summer Triangle. Deneb is the brightest star in the constellation Cygnus the Swan. Within the Swan is a small asterism called the Northern Cross because it looks like a sideways-oriented cross with Deneb at the top of it.
To make it into a swan, make Deneb the tail of the Swan and the star Albireo at the foot of the cross the head of the big heavenly bird. Then extend both ends of the crosspiece to make a curved wingspan, and there you have it, Cygnus the Swan on the wing.
Deneb may be the faintest of the Summer Triangle stars, but that’s only because it’s so far, far away, at least 1,500 light-years. It’s a humongous star that could be over 175,000 million miles in diameter, and our own sun isn’t even a million miles across. The light we see from Deneb tonight left that star in 500 AD.
By the way, the star Albireo at the foot of the Northern Cross (or the head of the Swan) is the best double star in the sky. Even with a small telescope, the seemingly mundane star is revealed as a gorgeous, colorful pair about 400 light-years away. One star is a pale orange and the other is a very distinct blue. Don’t miss it.
The star on the lower right-hand corner of the Summer Triangle is Altair, the brightest star in the constellation Aquila, the headless eagle. Altair and four other stars form a large vertical diamond that outlines the eagle's wingspan. Altair is the closest to us of the Summer Triangle stars, at just a little over 16 light-years away.
What’s really unusual about Altair is that it rotates once on its axis in only 10 hours, and it takes our sun about a month to accomplish the same thing. Because of its rapid spin, Altair is much wider at its equator than at its poles. You can’t tell by looking at it though, even with a large backyard telescope.
There you have it, the Summer Triangle. It covers a large chunk of the summer sky. Along with helping you find the three constellations within it, you can also use it to easily find nearby constellations like Hercules the Hero, Draco the Dragon, Delphinus the Dolphin and many more. Don’t go stargazing this time of year without it.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is also the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and at adventurepublications.net. Contact him at mikewlynch@comcast.net.
