Happy Tenth, Cassini!

Cassini has been at Saturn for ten years now. Ten years! From among my favorites:




As always, see the Cassini home page for more.

Happy Tenth, Cassini!

Cassini has been at Saturn for ten years now. Ten years! From among my favorites:


Wow... sunlight filtering through and reflecting off the rings to illuminate Saturn's southern hemisphere while the north remains in darkness. Note how dark the B-ring looks, its density blocking the sun's light. Below lurks Tethys, barely visible.

We keep seeing wondrous things through Cassini's eyes. Prometheus (102 kilometers, or 63 miles across) is seen here with two long streamers of material that it has pulled out of the F ring. When Prometheus comes close to the F ring in its orbit, the moon's gravity tugs on the ring particles. The disturbed particles, now pulled into orbits slightly closer to Saturn and therefore faster, shear out during successive orbits, creating the long and delicate streamers seen here.


Three of Saturn's smaller moons and its rings - from Mimas (at the top outside the rings altogether, 397 kilometers, or 247 miles across) to Pandora ( outside the F ring and 84 kilometers, or 52 miles across) to little Atlas (to the left, between the F and A rings and only 32 kilometers, or 20 miles across). This picture was taken from below the rings by Cassini in September 2007; doesn't it appear as if we're looking down, though? But we're looking up, so Pandora is closest to us, not farthest!


As always, see the Cassini home page for more.

Happy Tenth, Cassini!

Cassini has been at Saturn for ten years now. Ten years! From among my favorites:

There are four moons here:



The most obvious one is Dione, of course, bright and in the center of the shot. Behind Dione is giant Titan. Off to the right, at the tip of the rings, is little Pandora, an F-ring shepherd. Did you find the fourth one?

Look at the rings. See the dark gap? That's the Encke gap. Look closely. See the bright speck? That's Pan - tiny, tiny Pan, only 35 km (21.7 miles) across. Pan is a ring shepherd, and helps maintain the Encke Gap, keeping it clear of ring particles.

Here's a truly stunning image from Cassini, Rhea and the rings. It's raw, unprocessed - and amazing.



What moon is that? How can a moon of Saturn be so centered on the A Ring?

Well, it can't. That's no moon, folks, that's a star! And it's behind the rings.

It's Mimosa, aka Beta Crucis, the bright left-hand star in the Southern Cross. The rings, being particles, let light through, and this star's so bright it looks as though it's in front.


Cassini took this picture in infrared (which is why it's dark) just as Rhea moved behind Saturn. Further out along the rings are Tethys and Enceladus at far left.

As always, see the Cassini home page for more.

Happy Tenth, Cassini!

Cassini has been at Saturn for ten years now. Ten years! From among my favorites:



Oh. My.


Cassini was above the ringplane when it took this picture - a slice of the entire ring system.

The rings are lit by sunlight from below; the light scatters through the rings' particles, but much of it bounces off their undersides and illumines Saturn's southern hemisphere. It also casts a shadow of the inner rings across the northern hemisphere - and Saturn's own shadow slices across the rings on the left side of the photo.

Oh. Wow.

Check this out. Looking down from above - Saturn and its shadow, the entire set of rings, one moon (Janus - center, outside the rings), and two stars (lower down, flanking the outer F ring) ... There are some "spokes" - cloudy irregularities - in the B ring, the darker section of rings in the center.

As always, see the Cassini home page for more.

Happy Tenth, Cassini!

Cassini has been at Saturn for ten years now. Ten years! From among my favorites:


This moody true color portrait of Saturn shows a world that can, at times, seem as serene and peaceful as it is frigid and hostile. Saturn's unlit-side rings embrace the planet while their shadows caress the northern hemisphere.
Janus (181 kilometers, or 113 miles across) is a mere speck below the rings, just left of the terminator. The view was obtained from about 15 degrees above the ringplane as Cassini continued its climb to higher orbital inclinations.

Dione and Atlas and the rings... Atlas? Yes - select the picture and look just below and to the left of Dione and behind the rings.

From 24 degrees above the unlit rings, Cassini gazes down at the A Ring, with tiny Pan in the Encke Gap and the F Ring at the far outside (the bottom of the shot). Saturn is visible through the ring.

As always, see the Cassini home page for more.

Happy Birthday, Christopher

Today is the birthday (1632) of the great architect, astronomer, geometer, and mathematician-physicist, Sir Christopher Wren, also founder of the Royal Society and renowned in his life for his brilliant scientific drawings (particularly those of the brain). Today of course he's best remembered for the magnificent buildings he designed, especially St Paul's Cathedral.

His epitaph is famous, particularly the last line:

SUBTUS CONDITUR HUIUS ECCLESIÆ ET VRBIS CONDITOR CHRISTOPHORUS WREN, QUI VIXIT ANNOS ULTRA NONAGINTA, NON SIBI SED BONO PUBLICO. LECTOR SI MONUMENTUM REQUIRIS CIRCUMSPICE Obijt XXV Feb: An°: MDCCXXIII Æt: XCI.

Here in its foundations lies the architect of this church and city, Christopher Wren, who lived beyond ninety years, not for his own profit but for the public good. Reader, if you seek his monument - look around you. Died 25 Feb. 1723, age 91.

Check his Wikipedia page for a gallery of his architectural work.

Four Moons

It's been quite a while, hasn't it? But here's another gorgeous photo from Cassini: four moons and the edge of the rings. Ids are below the photo - see if you can spot all four. (Select the photo for a bigger version; you might need it!)



The most obvious one is Dione, of course, bright and in the center of the shot. Behind Dione is giant Titan. Off to the right, at the tip of the rings, is little Pandora, an F-ring shepherd. Did you find the fourth one?

Look at the rings. See the dark gap? That's the Encke gap. Look closely. See the bright speck? That's Pan - tiny, tiny Pan, only 35 km (21.7 miles) across. Pan is a ring shepherd, and helps maintain the Encke Gap, keeping it clear of ring particles.

As always, see the Cassini home page for more.

Two Moons

It looks like a world and its moon, but it's not. It's two of Saturn's moons, captured by Cassini - great Titan and much smaller Dione.

Rhea and the Rings

Here's a truly stunning image from Cassini. It's raw, unprocessed, and brand new - and amazing.



more info here

What shines?

What moon is that? How can a moon of Saturn be so centered on the A Ring?

Well, it can't. That's no moon, folks, that's a star! And it's behind the rings.

It's Mimosa, aka Beta Crucis, the bright left-hand star in the Southern Cross. The rings, being particles, let light through, and this star's so bright it looks as though it's in front.


As always, see the Cassini home page for more.

Downstream of Prometheus

The shepherd moons keep the rings together ... more or less. This gorgeous shot shows the F Ring's smoky appearance just after a pass by Prometheus.



(As always, the Cassini site has the details.)

Mimas near

Cassini turns its gaze from Enceladus and Dione to take a picture of Mimas and, 180,000 kilometers (112,000 miles) further on, Saturn. (Compare with Mimas beyond Saturn here. And, as always, see Cassini's site for details.)

A portrait in ice

Cassini takes a gorgeous portrait of Saturn's second-largest moon, Rhea, with the unilluminated rings and Saturn itself in the background. Gorgeous. Simply gorgeous.


As always, visit the Cassini site for more

Shadow across the rings

No, not Saturn's this time: Pandora, the outer shepherd of the F Ring, casts a sharp, narrow shadow across the ring.


As always, see Cassini's home page for details.

Mimas beyond

Cassini looks across the span of the rings and catches the innermost of Saturn's major moons, Mimas.


(See Cassini's site for details.)

Anthe's Arc

Saturn's ring-and-moons system keeps getting more complex - or, rather, we keep learning more details of its structure. Earlier in its mission, Cassini found that Mimas holds a bright arc in place along the faint G ring, an arc that travels along the ring as Mimas orbits. Later it showed us that Pallene has a thin ring of its very own. Now, Cassini has confirmed that other moons (Anthe, pictured here, and Methone) have arcs - incomplete rings.

Those three little moons - Anthe, Pallene, Methone - orbit between Mimas and Enceladus, and Anthe and Methone's orbits are in resonances, perturbed by Mimas. This may be why they have arcs instead of a complete ring like Pallene.

(as always, see Cassini's page for more details)

F Ring and Moons

I haven't posted one of these in a while ...



From left to right, Pandora, the F Ring, the edge of the A Ring, and in the Keeler Gap Daphnis. The picture was taken from 1.2 million km or 700+ thousand miles; Pandora's overexposed so the details of the F Ring can be seen more clearly.

As always, see the Cassini site for details.

Springtime on Northern Saturn

It's springtime on Saturn's northern hemisphere. The shadows of the rings slip southward, and the colors out of space become easier to see, as do the storms. This natural-color shot was taken from over 900,000 miles (1.5 million km) from the planet.

as always, see the Cassini site for details

Rings, moons, and a star

Here we see two of Saturn's moons affecting the rings. No, no the bright spot below the F ring; that's not a moon. That's a star. But above it is Prometheus, twisting the F ring, and Daphnis is up towards the top, in the Keeler Gap, creating ripples in the A ring.

As always, see Cassini site for details.

Closer in and faster

Just as Pan in the Encke gap overtakes Atlas on a regular basis, so Atlas overtakes Prometheus, the F ring shepherd, just about monthly. Atlas isn't a shepherd, though it's a ring moon, living in the Roche division; Prometheus is one of the two that maintain the kinked and wispy F ring.