Cygnus the swan
By Vernon Whetstone Amateur Astronomer
Did you know there is a hole in Cygnus, the Swan? Well, perhaps not a “hole,” it is more like a cloud, but not like any cloud you have ever known.
We are following the Milky Way up from its south end in Scorpius and Sagittarius and have now come to the constellation Cygnus, the Swan which is very easy to find almost directly overhead looking east.
Cygnus has one of the three stars of the Summer Triangle—Deneb—as the tail star. Cygnus also goes by the name of the Northern Cross.
Now, for us to see what I am talking about we need to be in a very, very dark-sky place, the further away from city lights the better, or at least find a place where you can put any lighting at your back.
The Milky Way runs the length of Cygnus going from the beak star, Albireo, on the right, across to the tail. Looking carefully you will notice that the star trail of the Milky Way seems to split leaving a dark hole before coming back together again at the tail.
This “hole” is actually called “The Great Rift” and is really not a hole at all, it is a cloud. A cloud of dark material, mostly dust and gas, that make up the plane and edge of the galaxy.
It does not mean there are no stars there, it just means they are hidden behind the cloud. A fact astronomers were not aware of until they could look through the cloud with heat-seeking infrared photography.
There are two important dates coming up. The first is Friday, Aug. 1, which is Lammas Day, a cross-quarter day. What is a cross-quarter day? In the ancient calendars of England, Ireland, and Scotland. This cross-quarter day means it is about halfway between summer and the start of autumn, or summer is about halfway over.
The actual mid-point of summer is Aug. 7, at 12:41 am MDT. The ancient calendar had four quarter days—the solstices and the equinoxes. The cross-quarter days were usually religions holidays marking the midpoint of the season.
The second day is another “Super Moon,” which I much prefer calling a “Perigee Moon.” That is a much better description of what the day is. A perigee moon occurs when the moon is at its closest approach to Earth in its orbit which happens close to the time when it is actually full.
Both of those events happen on Aug. 10. In fact, this perigee moon will be the closest for the entire year.
The moon will be at perigee at 11:43 am MDT and will be full at 12:09 pm, a mere 26 minutes later.
As for being “super,” there will nothing particularly super about it. Here is a little experiment you can do to prove it. Go outside at about 7:09 pm MDT when the moon rises. It may look very large, but trust me, it isn’t.
Hold your fist at arms length, extend your pinky finger—that’s the little one—and place it over the moon. It will cover it completely. Now go back outside three hours later and use your pinky again to measure. See it will be the same size as when it came up. You can go back outside several more times, but the angular size of the moon will still be the same. It will cover the moon each time.
SKYWATCH: First quarter moon Sunday, Aug. 3. Moon and Spica on Friday, Aug. 1. Moon/Spica/Mars on Saturday, Aug. 2. Moon and Saturn on Monday, Aug. 4. Moon and Antares in Scorpius on Tuesday, Aug. 5.
NEXT WEEK: The galactic super highway and more astronomical blathering.