The Saturnian Ring System

 

Images taken of Saturn using the 127mm Meade Apo Refractor at the Jodrell Plank Observatory from 2014 until 2021

" Have you ever been sitting in a railway carriage reading a newspaper and as the train slowly pulled out of the station you cursorily looked out the window? For a moment you might wonder if you in the carriage is moving forward or whether the platform is moving backwards whilst you remain stationary. Living on any planet in a dynamic planetary system has similar associated issues of relative movement.

As an 'Earthling', we can watch our Sun rise in the  East and set in the West just  like clockwork measuring the length of the day and night. Similarly, every midsummer, the Sun at midday is higher in the sky than at midday in midwinter. The former wouldn't happen if the Earth stopped rotating about a North - South axis or if it rotated the other way around, the latter would not occur if the Earth's axis of rotation was perpendicular to it's plane of orbit around the Sun.

For time immemorial, mankind has viewed the night sky and wondered at the constancy of the stars and the constellations.  Our far ancestors did notice that a few stars seemed to move oddly against the backdrop of the constant heavens and these were called  the 'Planets';  Mercury, Venus, Mars, Jupiter and Saturn - 'planete' was the word used by the ancient Greeks to define these 'unusual stars' and literally means 'wanderer'.

Explaining the movement of the planets became a lot simpler for almost everyone, other than the 'Inquisition'', once we came to terms with the uneasy thought that the Earth and/or mankind wasn't at the centre of everything.

If you look closely at the above images of Saturn you will notice two things:

1. The 2021 image is not as sharp as the others from previous years.
2. The angle at which we see the Rings appears to change over time.

The 2021 image is not as sharp because this year Saturn is very low on our southern horizon, which means we are imaging it obliquely through more of  our turbulent and polluted atmosphere. The night we captured this image the air over Lowestoft was particularly volatile making obtaining a sharp focus extremely difficult. Whilst Saturn and Jupiter are currently low to the horizon as viewed from countries in the Northern Hemisphere, from Southern Hemisphere locations both these planets are currently presenting high in the sky. This is because of the Earth's axial inclination to it's orbital plane and its position on its 12 monthly orbit around the Sun. For the same reason, when it's summer in the UK it's winter in New Zealand.

The view of the Rings appears to become less oblique from 2014 to 2017 when they are at their most open and then begin to close such that in 2021 we can just make out the south pole appearing above the Rings. This closing of our view will continue until 2025 when we will view the Ring System edge on. After 2025, the southern Saturnian Hemisphere will experience what passes for Summer on a cold Gas Giant.

In reality the Ring System will not change fundamentally, just the angle at which it is illuminated by the Sun and the angle at which we view it!

Saturnoppositions-animated By <a href="commons.wikimedia.orgwikiUserTdadamemd" title="UserTdadamemd">Tdadamemd<a> - <a href="commons.wikimedia.orgwikiFileSaturnoppositions.jpg" ti

Understanding the meanings of 'ecliptic' and 'equinox' are key to understanding why our view of Saturn and the Saturnian Rings changes over time on a cyclical basis.

Earths_orbit_and_ecliptic By Tfr000 (talk) 0159, 15 March 2012 (UTC) - Own work, CC BY-SA 3.0, httpscommons.wikimedia.orgwindex.phpcurid=18705315

The majority of the major bodies of the Solar System orbit the Sun in nearly the same plane. This is probably due to the way the Solar System formed from a protoplanetary disk of dust and gas. Probably the closest current representation of the disk is called the invariable plane of the Solar System. Earth's orbit, and hence, the ecliptic, is inclined a little more than 1° to the invariable plane, Jupiter's orbit is within a little more than 1⁄2° of it, and the other major planets are all within about 6°. Because of this, most Solar System bodies appear very close to the ecliptic in the sky. If you live in the Northern Hemisphere and you currently look south you will see Saturn leading Jupiter west across the sky.

Saturn's rotational axis like Earth's is inclined at an angle to the ecliptic. The Earth has an inclination of 23.4 degrees and Saturn 26.7 degrees. An equinox occurs when the position of the Sun is directly over the planet's equator. Both Saturn and  Earth have two Equinoxes in their respective years but Saturn's year, its orbital period, takes 29.4571 Earth years. So Saturn's equinoxes occur approximately 15 Earth years apart whilst on our planet they happen every six months.

 

PIA14943-SaturnBehindTheRings-20180813 By NASAJPL-CaltechSpace Science Institute - <a rel="nofollow" class="external free" href="httpsphotojournal.jpl.nasa.govjpegPIA14943.jpg">httpsphotoj

Earlier I wrote that the Ring system will not change 'fundamentally' but it is wise to note that each ring is made from billions of pieces of ice and rock, varying in size from a grain of sand to that of an average house, all of which are constantly on the move. These Rings are thousands of miles wide but only between 10 and 100 metres thick. There are gaps between them which can be seen clearly in the above image taken by the Cassini space probe. If you look at the images captured at the Jodrell Plank Observatory you can  see the A, B and C Rings with the Cassini Division - the black gap between the A and B Rings.  Each Ring is a dynamic system moving and constrained by the influence of gravity, angular momentum and harmonic resonance. We live in a chaotic Universe, so enjoy Saturn's beautiful icy Rings whilst you can. Mankind's span is brief, so much in the Solar System appears constant but over cosmological timescales change is definitely the name of the game.

The Rings were probably formed by Saturn's gravity capturing asteroids, comets and small moons and smashing them up in a series of collisions. How long ago were they formed is still a matter for debate. As a result of findings from the Cassini probe and estimating age from the accumulation of contaminant pollution of the Ring material, some scientists believe the Rings formed fairly recently and within the last 100 million years. Other scientists believe that the Rings are much older and that a natural process of recycling could throw this estimate way off. As Sir Patrick Moore used to say " We will just have to wait and see". - Karl Seguine Community Outreach Coordinator at the Jodrell Plank Observatory.

Saturn's_Rings_PIA03550 By NASAJPL - httpphotojournal.jpl.nasa.govcatalogPIA03550, Public Domain, httpscommons.wikimedia.orgwindex.phpcurid=610237

Saturn's_rings_in_visible_light_and_radio NASA