APOD: Saturn: Shadows of a Seasonal Sundial (2011 Oct 12)

[APOD Robot]

Saturn: Shadows of a Seasonal Sundial

Explanation: Saturn's rings form one of the larger sundials known. This sundial, however, determines only the season of Saturn, not the time of day. In 2009, during Saturn's last equinox, Saturn's thin rings threw almost no shadows onto Saturn, since the ring plane pointed directly toward the Sun. As Saturn continued in its orbit around the Sun, however, the ring shadows become increasingly wider and cast further south. These shadows are not easily visible from the Earth because from our vantage point near the Sun, the rings always block the shadows. The above image was taken in August by the robotic Cassini spacecraft currently orbiting Saturn. The rings themselves appear as a vertical bar on the image right. The Sun, far to the upper right, shines through the rings and casts captivatingly complex shadows on south Saturn, on the image left. Cassini has been exploring Saturn, its rings, and its moons since 2004, and is expected to continue until at least the maximum elongation of Saturn's shadows occurs in 2017.

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[mactavish]

The many images of Saturn relayed to us by Cassini are absolutely fascinating. If only Galileo could have seen them. We are soooooo fortunate!

[owlice]

Fortunate indeed! Stunning image. (Stunning planet!)

[simonate]

so peaceful, so beatiful

[nstahl]

Great image, great APOD.

Does anyone know what fraction of the sunlight the rings actually block from Saturn in, e.g. the season we're viewing? I'm thinking they could really complexify the atmospheric dynamics if there are those giant areas of real shadow that move slowly over the hemisphere. In the picture it looks like dense shadow but that could be a photographic effect. Or is Saturn so far from the sun that solar heating plays only a small part in its atmospheric dynamics? Or does anyone know yet?

[zbvhs]

What exposure times are required to capture images such as this one? Is blurring of the rings caused in part by motion of ring material during long exposures?

[orin stepanek]

Beautiful photo. Truly Cassini is a die hard probe. So are the rovers on Mars. Which would you say taught us more!
I really never thought of the rings being like a sundial; but that does make sense!
Bad hair day?

Click to view full size image

[Indigo_Sunrise]

AWESOME image! I always find Cassini's B&W images interesting - really emphasizing the dramatic! (Although when the images have color added, they are intriguing in new and different ways.)

Great image, great APOD.

Does anyone know what fraction of the sunlight the rings actually block from Saturn in, e.g. the season we're viewing? I'm thinking they could really complexify the atmospheric dynamics if there are those giant areas of real shadow that move slowly over the hemisphere. In the picture it looks like dense shadow but that could be a photographic effect. Or is Saturn so far from the sun that solar heating plays only a small part in its atmospheric dynamics? Or does anyone know yet?

What exposure times are required to capture images such as this one? Is blurring of the rings caused in part by motion of ring material during long exposures?

nstahl and zbvhs, many of your answers can be found here.

[moonstruck]

I gave my $400.00 telescope away several years ago after I started watching IPOD. What good does it do to see a little pin prick of light through a telescope when IPOD gives you the whole enchilada . Thanks NASA team.

[BMAONE23]

One of the things that I find more striking is the appearance of a tenuous atmosphere in the image at the equator. You can just see the rings through it giving the appearance that Saturn has a Hard Surface

[moonstruck]

That would be APOD. I don't even own an IPOD.

[alphachap]

The many images of Saturn relayed to us by Cassini are absolutely fascinating. If only Galileo could have seen them. We are soooooo fortunate!

Too far to see from Jupiter's orbit, also the broken high-gain antenna (caused by relying on the shuttle as a launcher) didn't help.

[alphachap]

I really never thought of the rings being like a sundial; but that does make sense!

Is it a sundial if it doesn't tell the time of day?

[solarteedoh]

I thought it was a picture of a lady's leg wearing self-support hose. - 'scuse me, I'm off for a cold shower.
On a serious note - I've been viewing APOD for years and seen some stunning pictures. Sometimes, it makes you feel so insignificant that there is such majesty 'out there'

[Dampa]

Wonder if the ring shadows would be recognized by a barcode scanner?

[neufer]

Nodus-based sundial

[c]The shadow of the cross-shaped nodus moves along a hyperbola
showing the time of the year, indicated here by the zodiac figures.
It is 1:50pm on the 16th July, 25 days after the summer solstice.

A 1954 sundial, on St. Mary's Basilica, Kraków, Poland.
"Our days on the earth are as a shadow, and
there is none abiding.": 1 Chronicles 29:15[/c][/color][/b]

Is it a sundial if it doesn't tell the time of day?

Nodus-based sundial

<<One type of sundial follows the motion of a single point of light or shadow, which may be called the nodus. For example, the sundial may follow the sharp tip of a gnomon's shadow, e.g., the shadow-tip of a vertical obelisk (e.g., the Solarium Augusti) or the tip of the horizontal marker in a shepherd's dial. Alternatively, sunlight may be allowed to pass through a small hole or reflected from a small (e.g., coin-sized) circular mirror, forming a small spot of light whose position may be followed. In such cases, the rays of light trace out a cone over the course of a day; when the rays fall on a surface, the path followed is the intersection of the cone with that surface. Most commonly, the receiving surface is a geometrical plane, so that the path of the shadow-tip or light-spot traces out a conic section such as a hyperbola or an ellipse. The collection of hyperbolae was called a pelekonon (axe) by the Greeks, because it resembles a double-bladed ax, narrow in the center (near the noonline) and flaring out at the ends (early morning and late evening hours).

Nodus-based sundials may use a small hole or mirror to isolate a single ray of light; the former are sometimes called aperture dials. The oldest example is perhaps the antiborean sundial (antiboreum), a spherical nodus-based sundial that faces true North; a ray of sunlight enters from the South through a small hole located at the sphere's pole and falls on the hour and date lines inscribed within the sphere, which resemble lines of longitude and latitude, respectively, on a globe.>>