Observed on September 12, 2011, approximately 8:30 pm CDT
This past Monday night (September 12) was beautiful in Chicago. Temperatures were warm but not humid, and the breeze was light. It had the feel of summer’s last hurrah. In other words, it was the perfect evening to dine outdoors, which is exactly what my husband and I did.
Sitting on a patio at a restaurant somewhere in the West Loop on a Monday night was like being in a calm oasis (complete with a bottle of wine). The restaurant courtyard included a gazebo, shade trees, and a nicely landscaped lawn, and the Harvest Moon was slowly rising above the skyline. In other words, it was as idyllic a setting as one could hope to have in the city.
I could not help but look up at the sky from time to time, which brings me to the second of my urban skywatching nights. I didn’t set out to look at the stars; rather, it felt like a natural thing to do. The setting was the perfect blend of the urban and natural worlds, and the stars and moon above were simply one part of it. You don’t need a special occasion to look up at the sky, after all.
One of the most obvious sights was the beautiful full moon, the Harvest Moon, rising in the east. At one point, there was a cloud directly underneath the moon that looked like a silver path climbing up to it.
Later, I saw the bright flash of a meteor. What an unexpected surprise! I wonder just how large an object it had to have been in order to burn brightly enough to be seen in the city.
My chair was facing south, and when I looked straight up, there was the bright star Vega (in the constellation of Lyra, the lyre). It is easy to spot: simply look straight up at any time in the early evening, and it’s the brightest point of light (and likely the only one) you will see directly overhead.
Here are some interesting facts about Vega:
- It is the fifth brightest star in all of the night sky (and fourth brightest in the Northern Hemisphere). Only Sirius, Canopus, Arcturus, and Alpha Centauri are brighter. And at this time of year, only Arcturus is visible (and it is low and setting in the west).
- When astronomers were first developing a scale to describe the brightness of stars in the sky, Vega was originally the standard reference star, the one all others were to be measured against. In other words, Vega was Star Zero (a bit like zero milestones for measuring distances to cities here on Earth). Later, the scale was refined and redefined, but Vega’s apparent magnitude is still close to zero (0.03, to be precise).
- Jodie Foster visited it in the movie version of Carl Sagan’s novel Contact.
- One reason it is so bright is that it is relatively close to us, “only” 25 light-years away.
An aside about constellations: The constellations don’t have the same significance for us city dwellers as they did for our ancestors who enjoyed dark skies. Most of the stars they saw are impossible for us to see, and it would take a lot of imagination for us to connect the dots and see the people and animals they were supposed to represent. These days, for astronomers, they are more like countries on a map of the sky, with well-defined borders and points of light representing cities and towns.
Vega is part of the Summer Triangle, a pattern of three bright stars (from three different constellations) so named because during the summer months, they can be seen somewhere in the sky for most, if not all, of the night. Even now, as fall approaches, the Summer Triangle is prominent.
The other two stars of the triangle are also easy to spot. Deneb (in the constellation of Cygnus, the swan) is the bright star to the left and slightly below Vega. Altair (in the constellation of Aquila, the eagle) is the bright star well below Vega. As you can see from my sketch, I also saw four other stars in the vicinity: three near Deneb and one near Altair. More on these in Part 2.
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As appetizer turned to entree to dessert, Vega slowly descended westward from its summit at the top of the sky. We spent about two hours at dinner, giving me a preview of what the sky would look like about a month from now. As the Earth advances in its orbit, Vega (and all other stars that rise and set) will set earlier and earlier until it finally disappears behind the sun in January.
Next time: Other stars in Cygnus and Aquila.