Analemma Dilemma   Leave a comment

Analemma_fishburn

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°:

analemma2010_ladanyi_c

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:

LunarAnalemma_richins_c72

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:

MarsAnalemma_Mammana720c

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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