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Summer solstice 2017 June 19, 2017

Posted by aquillam in Astronomy, MichiganAstro.
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The June Solstice occurs at 04:24 UT on June 21, 2017. That’s just after midnight EDT, so for most of the US the solstice falls on the 20th!

Here in Ann Arbor, the longest day of the year will actually be the 20th, despite the solstice falling on the 21st. That’s because we’re far west in the time zone, our clocks are ahead of the Sun. A bit farther east, say in New York, the 20th and 21st are basically equal in length. That’s more what you’d expect for a solstice close to midnight.

So enjoy the half second or so of extra darkness on the solstice.

Saturn Opposition 2017 June 16, 2017

Posted by aquillam in Astronomy, MichiganAstro, Urban Observing.
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It’s summertime, and that means Saturn-time!

But why is that?

A year on Saturn is a bit more than 29 years on Earth, which means Saturn moves about 12º along the ecliptic each year. For comparison, the Moon moves about 15º per day, so in a whole year, Saturn’s position will change less than the the Moon changes in a single day! It fact it’s so little that it take Saturn an average of two years to move through each zodiac constellation. Last year Saturn crossed the boundary into Ophiuchus (between Scorpio and Sagittarius), and it won’t leave until December. That means Saturn will be visible in the evening at about the same time this year as it was last year.

Ophiuchus is often called the 13th zodiac because itt sits between Scorpio and Sagittarius

Saturn takes 29 years to make a complete circuit of the ecliptic

Of course 12º isn’t nothing. Each year opposition drifts just a little farther east along the ecliptic, so the date changes. And since there are 360º in a circle and 365 days in a year, the date corresponds to roughly a degree per day! This year, opposition was June 15th. In 2016, it was June 3, and in 2015, May 23. Next year, opposition will be June 27.

By the way, opposition is when something (like Saturn) is opposite something else (like the Sun) in the sky. So when Saturn is at opposition, it rises at sunset, then sets at sunrise. Each night it rises a little earlier, so the weeks following opposition are the best time for evening observers to get a look. Closest approach is always close to opposition too, so the planet will be bigger and brighter than usual.

elpOrbitsOpp

At opposition, the Sun, Earth, and outer planet are on a line with the Earth in between.

elpOrbitsClose

Because the orbits aren’t circles, the Earth may get closer to the outer planet a few days before or after opposition.

 

So enjoy summertime Saturn while you can. In about 4 more years, it’ll be fall when Saturn’s out.

Lyrid meteor shower 2017 April 17, 2017

Posted by aquillam in Astronomy, MichiganAstro.
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The first potentially big warm weather meteor shower is coming this weekend. Predictions of the peak’s timing all place the peak during daylight in the Midwest on the 22, but this shower usually has an extended peak. In fact, you may see as many meteors on the 21 or 23.

The radiant lies in Lyra, near Hercules. It’s not really high enough to observe until 2 AM, it transits the meridian around 5:30, and it starts getting light out at about 6 AM, so the best time to observe is about 4 – 6 AM local time. Here’s a map for 5 AM with the stars of the summer triangle marked:

22Apr0500S.png

The Lyrids are an irregular shower, usually producing a mere 10 – 20 meteors per hour, but occasionally reaching rates of around 100 meteors per hour.   This year is expected to be a pretty average year, which means waiting several minutes between meteors. If you don’t have dark skies, it may mean 10 – 15 minutes between bright meteors.

 

Additional resources:

American Meteor Society guide to the Lyrids

EarthSky All you need to know: Lyrid meteors

 

NASA image & Video Search April 14, 2017

Posted by aquillam in Astronomy.
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NASA has launched a new portal to make it easier to search their vast multimedia collection. Try it out with your favorite object!

https://images.nasa.gov/