Astronomy Picture of the Day 3-20-03

NASA ^ | 3-20-03 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2003 March 20

Sunrise Analemma
Credit & Copyright: Anthony Ayiomamitis

Explanation: Astronomically speaking, at the Equinox on March 21, 0100 UT (March 20, 8:00 PM ET) the season changes. For this Equinox the Sun rises due east as it crosses the celestial equator heading north. In celebration, consider this spectacular sunrise analemma! 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. In this remarkable case, 38 separate exposures (and 1 foreground exposure) were recorded on a single piece of film between January 12 and December 21, 2002 at 06:00 UT. The tilt of planet Earth's axis and the variation in speed as it moves around its elliptical orbit combine to produce the predictable analemma curve. The top and bottom of the figure-8 correspond to the Solstices -- the Northern and Southern limits of the Sun's sky motion. The two Equinoxes find the Sun at points along the analemma curve exactly half way between the Solstices. Here, the analemma's Southern portion is partly hidden by mountains. In the foreground lie the stone ruins of the Tholos at the ancient site of Delphi, Greece.

[petuniasevan]

The analemma curve is dependent on 2 factors.

First of all, the Earth is tilted 23.5 degrees with respect to its orbital plane.

Second, the Earth's orbit is not a circle but an ellipse. Perihelion occurs January 2nd.

If you were observing the analemma from another planet, say Jupiter, its appearance would be different. Jupiter is tilted only 3 degrees from the perpendicular, but has a fairly elliptical orbit, so the solar analemma appears there to be a simple oval.

On the other hand, the analemma from a Uranus-based location is a very wide and even figure-eight. Uranus is tilted past "sideways" to an angle of 98 degrees. Its orbit is about as elliptical as Jupiter's and more elliptical than Earth's.

[petuniasevan]

[petuniasevan]

Good news. So far, there has been no problem with posting images from other (reliable) servers.

I will continue to post APOD unless something unforeseen causes Jim or John to restrict such non-news threads.

Thanks for your support.

[MeekOneGOP]

bttt

[xJones]

Thank you for your fascinating threads that provide a real uplift in the morning. In these days, it really helps.

[GodBlessRonaldReagan]

Thanks for the ping!

[RightWhale]

the Tholos

The makes a nice picture, the best ruin left at the site. It's not very big, and its use is not at all clear, probably they sold shish-ka-bobs. It looks like a late addition to the site, one of the artistic anomalies that is created when a society is in decadence. Delphi was a favorite picnic spot for wealthy Athenians--they had everything just like the state fair. Racetrack, concessions, fortune-tellers, you name it. The sky is very clear and it is far enough from Athens that city lights are not much of a problem. The Grotto no longer gives off fumes, and the show is over.

[firewalk]

Thank you

[petuniasevan]

its use is not at all clear, probably they sold shish-ka-bobs

So it might have been an ancient fast-food outlet?. Oh well. Perhaps archaeologists of a later age might ooh and ah over the ruins of the mysterious golden arches...

[RightWhale]

Some ruins you can see what they were, what they did, what they were used for. But that one looks like something from the knick-knack shelf. A person coud climb all over it all afternoon and still not have a clue, no vibes. If it wasn't a monument to the ancestors of one of the wealthy Athenian families before they got overrun by Spartans, I would guess a kiosk: candles, cheese and crackers, moist towelettes.