June has fewer hours of darkness than any other month. The solstice occurs June 20, and because the name literally means the sun is standing still, the daylight hours a couple of weeks before and a couple of weeks after the solstice show very little change.
In Durango on the 20th, the sun will rise at 5:51 a.m. and set at 8:35 p.m., giving us a few seconds less than 14 hours and 44 minutes of daylight. However, that doesn’t mean there are over nine hours of astronomical observations that can be made. After the sun has set, there are several stages of twilight that play a role in what we can see in the night sky.
Immediately after sunset is what is called civil twilight, and that lasts until the sun is 6 degrees below the horizon. The sky is still quite bright, and typical daylight activities are possible without any extra assistance. Walking and gardening might even be more pleasant during this time, and car headlights are much more important for being seen than for helping you to see the road ahead. Because the sky is so bright during civil twilight, astronomical observations are ruled out. On the solstice, civil twilight includes the time after 5:20 a.m. and before 9:06 p.m.
The time when the sun is between 6 and 12 degrees below the horizon is called nautical twilight. Historically, it means you can still clearly make out the horizon when navigating a ship on the ocean. Many of the brighter stars are beginning to appear. During star parties, this is the time used for looking at the moon and planets through a telescope. Nautical twilight is after 4:41 a.m. and before 9:45 p.m. on the solstice.
Astronomical twilight is the time when the sun is between 12 and 18 degrees below the horizon. Many stars are out, and most people would call this dark. Bright clusters and galaxies can be seen, and this is what most people attending public star parties experience.
However, anyone trying to find really dim objects through their telescope knows it’s not yet truly dark. On the solstice, astronomical twilight ends at 10:28 p.m. and begins again at 3:57 a.m. That gives us less than five and a half hours of true darkness, and means serious stargazing can only happen after a reasonable bed time.
This monthThe summer Milky Way rising near the end of astronomical twilight is one of the most spectacular sights in the night sky. The brightest part is near the constellation Sagittarius and has dozens of interesting clusters and nebulae that can be seen with the naked eye.
Just before 11 p.m., the planet Jupiter rises, and that is followed by Saturn about 15 minutes later. Both planets will be in conjunction with Earth next month, meaning they are at their closest approach and should show the best views through a telescope.
Globally speaking, the biggest astronomical event this month is an annular solar eclipse, but you would need to be on the other side of the world to see it. An annular eclipse happens when the moon crosses in front of the sun at apogee, or when it is in the part of the orbit that is farthest from Earth. In this case, the moon appears slightly smaller than the sun, so you get a ring of sunlight around the dark interior. Some of you may remember the annular eclipse near Durango in 2012.
On the evening of July 4, besides fireworks, you will be able to see a penumbral lunar eclipse. That is where the moon passes through a part of the Earth’s shadow, but only dims slightly. You would need to pay attention that the full moon dims slightly during the night, so don’t get distracted with fireworks in case there are any of those.
By the way, there was another penumbral lunar eclipse June 5 that I saw referenced on social media, but like the annular eclipse you would have had to go to the other side of the world to see it.
Charles Hakes teaches in the Physics and Engineering Department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at firstname.lastname@example.org.