Monday the summer of 2010 begins at least astronomically with the summer solstice. It’ll be the longest day of the year. The sun will reach its highest point in the Northwest sky.
Monday is the day that the Northern Hemisphere receives the maximum amount of solar radiation as the noontime sun shines directly over the Tropic of Cancer.
That line of latitude is 23.5 degrees north of the equator. In Everett, at 48 degrees latitude, the noontime sun won’t be quite at the zenith, but it’ll be close at more than 65 degrees above the southern horizon.
The sun rises in the northeast at 5:09 a.m. and sets in the northwest 16 hours and 3 minutes later at 9:12 p.m. Because the sun is taking such a high arc across the sky morning and evening twilight goes on a lot longer than it does in winter.
All of this doesn’t leave much darkness for summer stargazing, and there’s much more humidity in the air, which can really muddy the visibility as added moisture amplifies the effects of light pollution.
Take some time under the summer canopy of stars and pan your eyes among the constellations. For extra credit, stay awake long enough to take in morning twilight and follow the advice of Jack Horkheimer, longtime host of the PBS weekly show “Stargazer”: Relax, sit back and face the northeast about an hour before sunrise and take in all the sights and sounds. No cell phones, no radio, just you and your senses.
I don’t recommend that you set off on your all-nighter for the next week to 10 days because the first full moon of the summer is taking over the night sky. The actual date of the exact full moon is Saturday, but all this week our lunar neighbor will be washing out the celestial dome with its secondhand reflected sunshine.
The full or near-full moon this time of year takes a low track across the southern sky. In fact it takes pretty much the same low path that the sun does around the winter solstice, the first day of winter. That makes sense because the geometry of the full moon is such that it’s always on the opposite end of the sky from the sun.
If you’re up before sunrise on Saturday morning enjoying the full moon before it dips below the southwestern horizon, you’ll witness a lunar power failure. After 2 a.m. the upper half of the moon will start to darken, and by early morning the moon will really black out. That’s the result of a partial lunar eclipse as the moon in its orbit around Earth slides across the upper portion of Earth’s shadow.
This can only happen when there’s a full moon, but it doesn’t occur every full moon because the plane of the moon’s orbit around the sun is inclined by 5 degrees from the Earth’s orbit around the sun.
During most full moons the moon either passes above or below the Earth’s shadow against the sun, but this time around the moon is just catching the edge of the shadow. On the first morning of winter, Dec. 21, there will be a much more magnificent total lunar eclipse. Put this on your calendar.
Mike Lynch is an astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores. Check his website, www.lynchandthestars.com.
The Everett Astronomical Society: www.everettastro.org/.
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