This week in What’s Up is a reminder that the solstice is next week on June 21 and officially marks the beginning of summer here in the Northern Hemisphere. Throughout history, this time has been marked by festivals of different sorts, though some cultures considered the summer solstice the middle of summer, rather than the beginning of summer as it is in modern calendars.

The solstice means that the Sun will evenly illuminate both sides of the Earth, making day and night the same length. Another interesting phenomenon you can see with the unaided eye are objects not casting a shadow because the Sun is directly overhead. The furthest north this can happen is the Tropic of Cancer, 23.5 degrees north latitude, and it happens around the Summer Solstice in the Northern Hemisphere. Similarly, the farthest south it can happen is the Tropic of Capricorn at 23.5 degrees south when it happens on the Southern Hemisphere’s Summer Solstice six months later. The only place in the U.S. where this latter phenomenon is visible is in Hawaii, which is between the Tropics of Cancer and Capricorn.

Summer officially starts at the summer solstice, and this year, that means June 21 at 09:13 UTC, or 5:15 am Eastern. This seasonal change also means that days will start getting shorter and nights longer, finally. The Sun still being up at 20:00 local time just feels wrong on some level to some people, including me. Maybe that’s why I seem geared to a 2 am to10 am sleep schedule, unlike most other people I know.

Plus, that darn day star interferes with the darkness necessary to see various astronomical objects such as the planets, though you can see Venus during the day if you know exactly where to look and you’re very lucky. Speaking of the planets, they are getting higher and higher earlier and earlier in the evening, so they will be easier to see at a more reasonable hour soon. Not everyone has the ability to stay up late waiting for them to be high enough in the sky.

Sometimes all you can do is take a quick peek just before bed, and that’s fine. If you’re going to look at them through your telescope, you should try to set it up outside for a while before you start observing, to allow the temperature differential between the telescope and the outside air to equalize otherwise air currents in the telescope’s tube may degrade the views somewhat. This effect is more pronounced in closed tube telescopes with large optics, such as Maksutov Cassegrains, and less of an issue with other telescopes, such as truss tube Dobsonians.

But I think I’m getting away from the point of this segment. Circling back to the heat of summer.

You might think that the solstice would be the hottest time of the year. However, the hottest time of the year in the northern hemisphere usually isn’t until late July or early August for a variety of reasons. The main reason is that it takes time for the Earth’s land and oceans to absorb all of that extra heat, reach maximum absorption capacity, and start radiating heat back out. This is called the lag of seasons.

Another reason July and August are usually hotter is the precipitation or lack thereof. Precipitation, which is generally accompanied by wind, can cool the air and lower the overall temperature. June tends to see more rain than July and August, meaning it tends to be cooler than later in the summer. I wrote much of this segment during a small thunderstorm where I live, which was both nice to listen to and caused a much-appreciated drop in temperature.

One more event to look forward to is the impressive planetary alignment in the early morning of June 24. Jupiter, Saturn, Mercury, Venus, and Mars, as well as the Moon, will all be visible in one arc across the early morning sky. We talked about this last week, but it’s worth reminding you so you don’t miss it. The alignment only happens once every eighteen years or so.

I hope you take time out of your evening, however hot it may be, to look up and enjoy the night sky.

More Information

Lahaina Noon: When Shadows Disappear (Amusing Planet)

Why is August the hottest month of the year? (The Weizmann Institute of Science)