Hunting For Treasure In The Summer Triangle

The Summer Triangle is right on schedule with the season. Watch for the trio of Vega, Deneb and Altair across the eastern sky at nightfall.

The Summer Triangle invites our eyes to explore the eastern sky at nightfall. At dusk you’ll see Vega first, shining highest and brightest of the three stars that form the apexes of the triangle.

The others are Deneb in Cygnus the Swan (better known as the Northern Cross) and Altair in Aquila the Eagle. Vega heads up the small constellation Lyra the Harp.

All three are first magnitude or brighter; connect them by imaginary lines and you’ll make a triangle spanning 3 1/2 fists held at arm’s length or about 35 degrees.

Like the proverbial “X marks the spot” on a pirate treasure map, the Summer Triangle points sky watchers to a celestial hoard of star clusters, double stars and dark and bright gas clouds of all shapes and sizes. Many of these require a telescope or binoculars to see best, but not the Milky Way. All you need are your eyes and a dark sky.

The Northern Cross is outlined in the photo above. A bright patch of Milky Way stars occupies the bottom half of the cross, while a dark lane of  interstellar dust clouds splits the Milky Way down the middle. The dust blocks the light from more distant stars giving the galaxy a patchy texture. Photo: Bob King

The triangle corrals a particularly bright portion of the galaxy. The section in the bottom or southern half of the Northern Cross can even be glimpsed from suburban areas. As a kid living near Chicago years ago, I used to get up before dawn during the spring and summer months to catch sight of the Milky Way from Cassiopeia to as far south as Aquila. Why get up early? I’d heard that unnecessary city lights were turned off after midnight.

Other galaxies are bisected by clouds of interstellar dust along the mid-section. This is ESO510-G13. Dust is silhouetted against the galaxy’s many billions of stars.  Click to see more Hubble galaxy photos. Credit: NASA/ESA/Hubble Space Telescope

Last night a few of us were out in the driveway Summer Triangle gazing around 11 o’clock.   The big patch in the Northern Cross was very easy to see as was the Great Rift or apparent splitting of the Milky into two broad forks. What appears as empty space between them are really dark clouds of interstellar dust shed by previous generations of exploding and evolving stars.

The rift’s true nature took centuries to fathom. Only by the early 20th century did astronomers come to understand they’d been looking at dust all along and not empty space between the stars. Modern telescopes operating in the infrared and radio regions of the spectrum can now “see” into the dust and detect multitudes of stars slowly forming within the cold, dense cores of the clouds through gravitational collapse. Dust that was shed by stars long gone will one day become a new generation of stars as gravity coaxes the ashes to burn once again.

Our Milky Way galaxy is shaped something like a pancake. Where the butter is there’s a bulge in the disk where the stars are more concentrated.

The sun and planets are situated in the plane of our pancake-shaped spiral galaxy about 2/3 of the way from the center to the edge. Put yourself inside a pancake for a moment and imagine the Earth 2/3 the way from the butter to the edge.

There’s a lot more pancake (dough) between us and the center compared to looking straight up or down through the thin cake. In the real Milky Way, there are lots more stars between us and the center compared to looking up or down through the galaxy. The stars stack up along our line of sight to create a thick band of hazy starlight in the eastern sky we called the Milky Way. In other directions, the stars aren’t nearly so concentrated and simply appear as scattered jewels across the sky. The reason the stars look hazy is because most of them are so faint and far away their light mushes together into cloudy masses.

5 Responses

  1. Mike

    I am near Spooner WI this weekend had a great clear dark sky last night it was really amazing. Showed my parents Saturn, M8, M27, M13, and M31. They were pretty astonished being 65 and now for the first time seeing those things. Just wanted to share the report.

  2. Tim Fleming

    Hi Bob,
    I was wondering if you take suggestions for your column/blog – if you are, your Top 10 list for objects to look at with a binoculars in the summer sky.

    Enjoy the rest of your weekend.


Comments are closed.