Jared May: What's Up the Third Week of June, 2021

What’s Up This Third Week of June

The week ahead seems to promise several clear nights, except for the weekend when most stargazers and amateur astronomers are able to stay up the extra hours. The nighttime temperatures drop into the low 60s and high 50s so I would still pack a light jacket for stargazing.

Sunset this week is just after 9 PM so don’t expect to see the faint stars until 10 PM or later. Compared to last week (with the partial solar eclipse over parts of the US), this week is kind of slow in terms of astronomical events – but there is a ton in the sky to observe this time of year. This week be on the lookout for the first quarter moon, the summer solstice, the different levels of twilight, and overhead satellites.

Thursday June 17 is the first quarter moon. This means that at sunset, the moon will be roughly at its highest point in the sky. As the moon slowly advances through the first quarter phase and into the waxing gibbous phase, its light will block out more of the night sky. While this is the perfect opportunity to look at the moon with binoculars, telescopes, and even your naked eye, this is a frustrating time for astrophotographers (since the moon is so bright). In medium-dark to very-dark locations the moon affects your nighttime vision. After staring at the moon then looking away you may notice a bright glow left in your eyes. It takes about 10 minutes to really start adapting your eyes to the darkness.

The first quarter moon is a great time to observe its rough surface through a small telescope or binoculars.

Sunday June 20th is a special day – it’s the summer solstice. Sometimes when people are having a rough day they say “it has been a long day”, well Sunday will literally be the longest day of the year. The solstice should be a day for celebration, however, since it marks the official start of summer. The solstice happens when the sun reaches its northernmost declination (the highest path it can take in the sky) which is why the day will be so long. It will not be a huge jump in the number of hours of daytime, in fact, the day before and after the solstice is just six seconds shorter and less than one second longer respectively.

A simulated view of the sun at its highest point in the sky on the day of the Solstice.

The time after sunset is called twilight. This is (in my opinion) the time of most anticipation for stargazers and amateur astronomers since the sun has set and the wait has begun for the sea of stars to become visible. There are actually three phases of twilight before it officially becomes night (or day). After the sun has set we immediately enter into civil twilight. This is still a bright time where artificial lights are not required to see. When the geometric center of the sun is 6° below the horizon we enter nautical twilight. In this stage, the human eye can roughly identify objects outdoors, but cannot make out details. When the sun is between 12° and 18° below the horizon we enter into astronomical twilight. This is when the faintest stars begin to become visible and only silhouettes of objects can be seen. Try guessing what stage of twilight you are in based only on what your eye can and cannot see.

The sunset is a process that goes on long after the sun dips below the horizon. During the height of summer, the sun takes a long time to dip far enough below the horizon to allow the sky to be completely dark.

One of my favorite activities to do while stargazing with friends is to compete to see who can see the most satellites flying overhead. The satellites that can easily be seen are in low-earth orbit and circle the globe roughly every 90 minutes. Many of these satellites are only 250 miles above the earth’s surface, or roughly the distance from Cleveland to Cincinnati. These overhead satellites will appear to move at the speed of an airplane but will have no sound nor blinking lights. If you have a camera on a tripod and you take a long-exposure image (15 to 30 seconds, for example) you can likely see the long trails of maybe half a dozen satellites. The image below is a closeup of a star-trail image that has several small satellites and even a meteor. Can you spot them all?

Satellites usually look like “moving stars” and do not have flashing lights. The errant streak in this star-trail image is made by a satellite that moved over the course of the photo.

There will be several upcoming clear nights… just not over the weekend unfortunately. Get outside and enjoy the long days and track the twilight phases before stargazing through the comfortably warm nights. This week be on the lookout for the first quarter moon and hunt for overhead satellites by using your eyes or perhaps a long-exposure technique.

Clear Skies!