Archive for the ‘Analemma’ Tag

On The Cusp Of Summer   Leave a comment

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The Earth captured at summer solstice, 2017 – Credit: Japan Meteorological Agency’s Himawari-8 satellite

Ah, summer. Leisurely days spent sipping ice tea by the pool or barbecue. Or maybe a vacation on a beach or lake? Or a trip overseas? There’s just something about this favorite season of everyone’s that brings smiles and thoughts of relaxing the sultry days away, maybe indulging too much ice cream and gazing at fireworks.

Summer almost seems like a reward for shivering in winter, raking all those autumn leaves and pulling the enthusiastically growing spring weeds from all those places they shouldn’t be growing. It’s the glamour girl of the seasons, letting down its long, luxurious hair to blow in the west wind, shining brightly in the glittering sun.

But really, summer is just a spot on the Earth’s orbit that means that one of its poles has reached its maximum tilt towards the sun, and from an observer’s viewpoint, the sun has reached its highest point in the sky. And during the northern hemisphere’s summer, anyone south of the equator is entering winter. Or, if you’re at the equator, there’s hardly any shift in time or seasons.

The summer solstice occurs in the northern hemisphere anytime between June 20-22. It’s a quirk of the calendar, not of the Earth. If one also notices the time of sunrise and sunset, you’ll see that sunrise times seem stuck in place for a few days, but the sunset times grow later. The sun in the sky appears to be at the same place for a short while. That’s known as an analemma. Click on the link for a previous blog post that nicely explains what it is.

Skygazers are rewarded with lots of wonderful constellations during the summer. Facing south, both Scorpius and Sagittarius dominate the sky. There’s the Perseid meteor showers from August 8-13. The Summer Triangle too – consisting of three brilliant stars: Deneb in Cygnus, Altair in Aquila and Vega in Lyra. The Milky Way shines brightly above around midnight, and Aquila and Cygnus are poised within it.

While haze might make some nights a bit challenging for observing the sky, viewers should take every opportunity to turn off the porch light and look up. Those stars won’t be hanging around forever. They’re busy marching on to the next season, which is autumn, and in the northern hemisphere it occurs on September 23. So put down your smartphone, turn off the TV and get outside!

 

 

 

Analemma Dilemma   1 comment

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Afternoon analemma photo taken in 1998-1999 by Jack Fishburn in Murray Hill, NJ.  Bell Laboratories building in foreground

Have you ever noticed in the mornings, from about mid-December to around mid-January that the sun rises the same time every day?  Even though the time of the setting sun changes, the dawn keeps breaking at 7:21 am (or whatever time your sun happens to rise, depending upon where in the world you live).  It’s as if it’s stuck, needing an extra nudge to get it moving.    Once again, from about mid-June to mid-July, the same thing happens with the sun once more.

As illustrated in the photo above, this phenomena is called an analemma.  The Merriam-Webster dictionary defines it as, “a plot or graph of the position of the sun in the sky at a certain time of day (as noon) at one locale measured throughout the year that has the shape of a figure 8; also  :  a scale (as on a globe or sundial) based on such a plot that shows the sun’s position for each day of the year or that allows local mean time to be determined.”

So, if one were to take a picture of the sun at the same time every day, from exactly the same position, you’d more or less wind up with a figure 8.  It’s proof that the Earth’s axis is tilted at 23.439°.  However, the angle at which it’s seen changes wherever one is located on Earth.  The above was taken at roughly 40° north.  Here is a picture taken at Veszprem, Hungary, which is latitude 47°:

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Image Credit & CopyrightTamas Ladanyi – Analemma 2011 – taken at 9:00 am 

So at 47°, the sun’s angle’s a bit sharper.

Here’s an excellent link from the Washington Post that illustrates how the sun moves in the sky through the months.

And who can forget the moon?  Since it rises and sets, it too creates its own analemma.  However, the moon rises 51 minutes later every day, so in order to successfully photograph it, one has to take that into account.  Understanding that means the moon returns to the same position 51 minutes later, in accordance to its rising.  Still, with patience, one can create an excellent example of what the moon can do, although one has to also remember it has phases.  That creates a wonderful variety of shapes.  Here’s an example:

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Credit & Copyright: Rich Richins

Earth isn’t the only place where the analemma occurs.  Any planet where the sun shines also shares this perspective, although it’s teardrop shaped on Mars:

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Digital Illustration Credit & Copyright: Dennis Mammana (Skyscapes)

Why the different shape?  Here’s the explanation from NASA:

“On planet Earth, an analemma is the figure-8 loop you get when you mark the position of the Sun at the same time each day throughout the year. But similarly marking the position of the Sun in the Martian sky would produce the simpler, stretched pear shape in this digital illustration, based on the Mars Pathfinder project’s famous Presidential Panorama view from the surface. The simulation shows the late afternoon Sun that would have been seen from the Sagan Memorial Station once every 30 Martian days (sols) beginning on Pathfinder’s Sol 24 (July 29, 1997). Slightly less bright, the simulated Sun is only about two thirds the size as seen from Earth, while the Martian dust, responsible for the reddish sky of Mars, also scatters some blue light around the solar disk.”

Each planet, given its north-south axis tilt and shape of its orbit, has its own analemma shape:

  • Mercury – nearly straight line
  • Venus – ellipse
  • Mars – teardrop (as illustrated above)
  • Jupiter – ellipse
  • Saturn – figure 8, but with tight northern loop
  • Uranus – figure 8
  • Neptune – figure 8

Let me add that you don’t necessarily need a camera to record the sun’s analemma.  Think back to the movie “Cast Away” wherein Tom Hanks marks on stone where the sun travels throughout the year.  You can make note by just looking out the window and the same time each day, seeing where the sun happens to be at the same time each day.  It’s pretty cool.  Try it!

Posted January 14, 2015 by seleneymoon in Moon, Nature, Planets, Sci-Fi, science fiction, The Sun

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