B-Ring It On!

 

Saturn_s_B-ring_close-up

What do you think this picture might be? Could it be a microscope’s view of a hair? Could it be the pages of a really big book? They’re not bad guesses but they’re not correct.

This image focuses on a region in Saturn’s B ring, which is seen in twice as much detail as ever before, revealing a wealth of rich structure. It shows the incredible detail at which the international Cassini spacecraft is observing Saturn’s rings of icy debris as part of its dedicated close ‘ring grazing’ orbits. The spacecraft was at a distance of about 51 000 km from the rings

Saturn’s rings are composed mainly of water ice and range from tiny dust-size specks to boulders tens of metres across. Some of the patterns seen in Cassini’s close images of the rings are generated by gravitational interactions with Saturn’s many moons, these are known as shepherd moons which by their gravity help to keep the rings in shape by ‘kicking’ material into the rings or out into space. However many details remain unexplained.

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A Cassini image looking across Saturn’s rings showing where the B-ring lies.

The spacecraft’s ring-grazing orbits began last November, and will continue until late April, when the mission enters its ‘grand finale’ phase. During 22 final orbits Cassini will repeatedly dive through the gap between the rings and Saturn before plunging into the planet’s atmosphere in mid-September to conclude its incredible 13-year odyssey around the Saturn system.

If you want to see Saturn and its rings this is a good time to do it; Saturn rises about 2:15 in the morning in mid-March and an hour earlier by mid-April and lies in the constellation Sagittarius. That means for us that it is quite low in the sky. It gets to its highest point in the sky a little before sunrise, so you have a good chance of seeing it. (Sagittarius is a lovely constellation full of objects as when you look at it you are looking in the direction of the centre of our galaxy the Milky Way.)

You will need to look towards the East and South to see it but it will be the brightest object in that part of the sky.

To help you find it the moon will be either side of Saturn on the 16th and 17th of April.

Binoculars will show that it has a funny shape, almost like a rugby ball, and a small telescope will begin to show the rings. The rings are currently tilted towards us and will make for a lovely sight.

The Cassini-Huygens mission is a joint venture between NASA, ESA (the European Space Agency) and the Italian space agency ASI. It was launched from Cape Canaveral on the 15th. October 1997 aboard a Titan IV-B which is the NASA’s largest and most powerful rocket.

Published in: on March 26, 2017 at 12:14  Leave a Comment  
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Oh My!

The solar system is full of amazing sights; from aurora on Earth, to giant solar flares, to the great red spot there are countless objects to fascinate us. every now and then comes along something you just don’t expect. Often these are from objects you just wouldn’t imagine to be interesting (which just proves the old adage; ‘never judge a book by its cover.’)

The Cassini mission to Saturn (launched on October 15th. 1997 and arrived seven years later) is starting to wind down (sadly) and will soon be sent on a course that will see it fly through Saturn’s rings and eventually into the planet’s atmosphere to be destroyed. Despite that it is still providing us with surprises; the most recent being its images of the little shepherd moon Pan.

759Raw image of Pan. NASA. The grey lines either side of Pan are rings of Saturn!!

Looking through a telescope at Saturn from Earth the rings look quite simple; there

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appear to be two sets separated by  black gaps or ‘divisions’. the Encke division is very difficult to see and cuts around the A ring. The second gap is the Cassini division and is much easier to see, lying between the A and B ring. The image below also shows the C ring or crepe ring which is very difficult to see in amateur telescopes and is only hinted at in the above Nordic telescope image.

post-6974-0-24780700-1405571735Stargazer’s lounge image. (Just for clarity and because you can never have too many pictures of Saturn!)

This begs the question: how are the rings able to stay so neat? could it be gravity and that he material that makes up the rings be in just the right place that they don’t change?

Pioneer 11  became the first spacecraft to visit Saturn. It was launched from Cape Canaveral  on the 5th. April 1973. Pioneer 11’s path through Saturn’s outer rings took it within 21,000 km of the planet, where it discovered two new moons (almost colliding with one of them in September 1979) and a new “F” ring. Saturn from Pioneer looked very similar to Saturn through a telescope.

739508main_739460main_AC79-9107_3-full_full Pioneer 11 image of Saturn.

It wasn’t until the Voyager spacecraft flew past Saturn ( Voyager 1 in November 1980 and Voyager 2 in August 1981) that we began to realise what a complicated and far more extensive system the rings formed.

8bg                       Saturn’s rings with “spoke” features in B-ring. Aug. 22, 1981. Distance 2.5 million miles.

The spokes created much excitement and discussion and were endlessly replayed in a video sequence on TV…and to be honest I did and still could watch them happily for hours.

10bg The F-ring (discovered by Pioneer 11.) Two braided but separate orbit rings. Nov. 12, 1980. Range 750,000 km.

A clue to the structure of the rings was found by Voyager 1 when  it discovered three new moons, Prometheus, Pandora, and Atlas. Prometheus and Pandora are shepherding moons of the F-rings, and Atlas is a shepherd of the A-rings. After a lot of analysis and some careful thinking it was realised that these moons are able to control the movement (or shepherd) of material making up the rings by either pushing the material into place in the rings or ejecting stray material from the system all together. All this is done by the gravitational force of the much larger satellites on the smaller material that makes the rings. Pan creates stripes called “wakes” ( which are places where ring material has collected in an orderly manner) in the ring material on either side of it. Since ring particles closer to Saturn than Pan move faster in their orbits, these particles pass the moon and receive a gravitational “kick”. This kick causes waves to develop in the gap and also throughout the ring, extending hundreds of miles into the rings. These waves intersect downstream to create the wakes.

Pan has a similar shape to Atlas and that unusual shape may be the result of fine material from the rings aggregating on the surface of the moon.

A little more about Pan before we go: it was discovered on the 16th. July 1990 by Mark Showalter who was working on Voyager data. It is approximately 35 kilometres across and 23 km wide. It lies within the Encke Gap in Saturn’s A Ring. It orbits Saturn every 13.8 hours, at a distance of 134,000 kilometres and is responsible for keeping the 325 kilometre wide Encke Gap open.

There are many fascinating worlds around Saturn – have a look for Daphnis another shepherd moon as well as the ones mentioned above.

To give you an idea of the complexity of the ring system here is another image from Cassini:

pia20506-1041

 

 

 

 

 

 

Uranus; discovered today in 1781!

238 years ago today on the 13th. March 1781, amateur astronomer William Herschel discovered a new planet: Uranus.

He was surveying the night sky when he spotted what he thought was a comet. He soon realised that it was moving too slowly for a comet. That could mean only be one thing: a planet. It took a further two years of observation to decide on just what was the nature of this object.

uranus-cartoon_en

NASA

Uranus was the first planet to be found with a telescope. Herschel was later knighted for his historic discovery, probably helped by his trying to name it Georgium Sidus (George’s star) after his patron King George III. It took seventy years before the name Uranus was finally decided upon.

Uranus is a strange world as unlike the others it rolls around the Sun on it’s side; this is possibly the result of a collision with a very large object that knocked it over! In 1789 Herschel thought he detected a ring around the planet but it wasn’t until 1977 that rings were definitively observed from the Kuiper airborne Observatory.

PIA02963 Image from Hubble showing tilt, rings and atmospheric activity

Uranus takes 84 years to orbit the Sun and lies about 2.87 billion kilometres from the Sun. Uranus spins about its axis once every 17 hours 14 minutes, leading to a year that is 30,190 days long! A long time between birthdays. 

At magnitude 5.9, Uranus is not visible with the naked eye, but binoculars or a small telescope can reveal it as a tiny blue-green dot. It is beginning to become a real challenge to see Uranus now as the nights begin to shorten; it sets around 20:50, shortly after Venus. The easiest way to find Uranus is to locate Venus – which is the really bright object in the west at sunset. From Venus draw a line to the left and you will come to a feinter orange object, that’s the planet Mars. With your binoculars move down to the lower right of the sky and slowly sweep the area; you will make out a small object; that’s Uranus! See the map below.

 

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Finder chart from Heavens-Above.com