Skywatch Line for Wednesday and Thursday, July 12 and 13, 2023

This is Dudley Observatory’s Skywatch Line for Wednesday and Thursday,
July 12 and 13, written by Alan French.

The Sun rises at 5:28 A.M. on Wednesday and sets at 8:34 P.M. On
Thursday it rises at 5:29 and sets at 8:33. This Thursday has just under
8 ½ minutes less daylight than last Thursday.

The Moon was at last quarter Sunday and is now moving toward new. A
crescent old Moon is in the eastern sky before dawn.

If you look high in the south at 10:30 P.M. you’ll find the
constellation Hercules, the Son of Zeus, almost overhead. Hercules lacks
in bright stars, but its central shape is not hard to spot. Highest are
four stars outlining a keystone. Combining the keystone with two stars
lower in the sky, it’s not hard to picture the wings of a butterfly.
Other stars expand Hercules, mostly upward and eastward.

There are many capable apps that help you learn the sky available for
smart phones, tablets, and computers. They allow you to see the sky as
it appears at any time of night from any place on Earth. Most also
include a wealth of information about the objects that grace the night
sky. While they can be wonderful resources, they have one disadvantage,
it’s hard to dim them enough to preserve your night vision. Even the red
gels used by serious amateur astronomers don’t dim them enough to do the
trick.

As you’ve noticed, it takes our eyes time to adapt to the dark. When we
first go out under the night sky on a dark, moonless night, away from
city lights, we only see the brighter stars. We have trouble seeing
people and things around us. After a few minutes, more stars are visible
and we start to see the world around us. It won’t be in color and there
won’t be the detail we see in daylight, but, if we’re under the night
sky, we can get around, and many more faint stars are visible.

This increase in our eye’s sensitivity to light and improved view of the
stars and our surroundings continues for 30 minutes or more. Exposure to
a bright light or overly bright screen can ruin our “night vision” and
our eyes must adapt all over again for the best view the night sky.
Experienced amateur astronomers use dim red lights to read printed star
charts and preserve their night vision. Commercial red, “astronomer’s”
flashlights are available, and are usually adjustable in brightness.
It’s easy to make one from a standard flashlight by adding layers of red
plastic or paper. The light should be just bright enough to allow you to
see star charts when your eyes are fully dark adapted. (Today’s popular
bright, tactical flashlight is not a good starting point for a dim, red
astronomer’s flashlight. Unless designed for astronomy, headlamps and
flashlights with a red setting are generally far too bright.)

If you have a red flashlight tuned for your fully realized night vision,
a good, old-fashioned planisphere is a fine tool for learning the night
sky. A planisphere has a map of the entire sky that rotates within a
sleeve. You rotate the map to set the time and date. A window in the
sleeve shows the sky visible at the time and date you set.

Be sure to buy a planisphere that covers your latitude, Schenectady is
43 degrees north. Remember that planispheres don’t know Daylight Saving
Time (DST), it assumes you are using Standard Time. Set the planisphere
an hour earlier than the current time when we are on Daylight Saving Time.