Observing Saturn

Tips For Observing The Planet Saturn

Saturn, without objection, is the most beautiful planet in our solar system. I've often wondered that even if we could travel the galaxy, would we see another planet like Saturn and Saturn's rings.

Saturn is the 2nd to largest of our planets, and like Jupiter, is a gas giant. That means that Saturn is mostly composed of gas, with possibly a rocky or solid core deep within its cloudy exterior.

How many moons does Saturn have? According to a Saturn Wikipedia article at the time of this writing, Saturn has some 62 moons with confirmed orbits. It's a miniature planetary system in its own right. Most of the moons, however, are quite small, and not visible with amateur telescopes. But a half dozen or so are visible with amateur telescopes, depending upon the telescopes' size. Moon's that may be visible tonight are shown in diagrams further into this article.

The following table presents some interesting data about Saturn, like how big is Saturn, and how far away is Saturn.

	Saturn
Dia (mi)	74901
Rel Dia (to Earth)	9.45
Rel Mass (to Earth)	95.142
Rel Gravity (to Earth)	1.07
Min Dist to Earth (mi*e6)	746
Max Dist to Earth (mi*e6)	1036
Max Angular Size (arc-sec)	20.71
Min Angular Size (arc-sec)	14.92
Max Angular Ring Size (arc-sec)	48.39
Min Angular Ring Size (arc-sec)	34.84

As the table shows, Saturn is huge, nearly 75,000 miles in diameter. That's over 9 times the Earth's diameter. It is also much more massive than Earth, nearly 100 times as massive. So you'd think that Saturn's gravity would squash you if you could stand on a platform suspended at the top of Saturn's clouds (there's no solid surface at Saturn's measured diameter).

Not so. In fact, you'd feel only 1.07 g's if you could stand atop Saturn's clouds. It's very massive, yes, but you'd be standing much further from its center then you are from Earth's center.

The distances to Saturn from Earth, listed in the table, are in millions of miles. So Saturn varies from about 746 million miles to a little over a billion miles from Earth, as Earth and Saturn find themselves either on the same side of the Sun, or opposite sides as their orbits permit. This range changes the apparent size of Saturn, as viewed from Earth. The image below shows the way the Xephem ultiliy presents the relationships between Earth's and Saturn's respective orbital positions.

 

 

Saturn's angular size as viewed from Earth can thus vary from a minimum of about 15 arc-seconds to a maximum of about 21 arc-seconds. Not a vast difference really. That's about the apparent size of a medium sized 20 mile diameter crater on the moon. That's pretty small, and while the planet itself is easily seen in amateur sized telescopes, details on the planet are too small to be discerned.

Of course, Saturn's rings extend much further than the planet itself. How large are Saturn's rings? Saturn's rings are about 175,000 miles across. So from Earth, they look bigger than the planet, having an apparent angular range of from about 35 arc-seconds to nearly 50 arc-seconds. That's nearly the apparent size of Jupiter, even though Jupiter is only about half as far away.

So what can you see when looking at Saturn through a telescope? At right is an example of the impression of the ringed planet Saturn you might get on a good night through a small telescope. The image would actually be smaller, but you could perceive about this level of detail on a typical evening.

To get at least enough resolving power to clearly perceive Saturn's rings you will need at least a 2 inch telescope. Of course, the bigger the telescope, the more detail you will likely see, such as the Cassini Division. I have seen for myself, in 2013 when Saturn's rings are well tilted, the Cassini Division with a Long Focus 60mm Telescope, home constructed as indicated on the linked page. I will admit, however, that when the ring tilt is very shallow, a 60mm might not be able to reveal the Cassini Division.

A great choice for a telescope for Saturn viewing is a long focus refractor. Something like the Orion AstroView 90mm Equatorial Refractor Telescope would work very well. I observe planets routinely through a quality 60mm refractor of long focus, and get very enjoyable views. Superb views of Saturn can be obtained with a 4 inch refractor, but nice views through any quality refractor telescope are routine. I've even obtained good views of Saturn, Jupiter, and Mars with my quality 50mm refractor.

Refractor telescopes perform well because they tend to cool down to ambient temperature quicker that other telescope types and give steadier views. They also give the highest contrast views for a telescope of any given aperture.

You can see Saturn and possibly 4 or 5 if its moons at low power, between 50x and 100x. To see the rings in some detail, you'll need to move to 100x or better.

Another good choice for observing Saturn is a Maksutov telescope. Even a 90mm (3.5 inch) version will easily show the Saturn's rings and likely the Cassini division, the dark gap in the rings.

Maksutov telescopes like the Celestron NexStar 90SLT Mak Computerized Telescope are also renowned for their crisp images that are free of chromatic aberration. They also have high focal ratios and thus long effective focal lengths, making them ideal for planetary observing. While they can't quite match up to the contrast of an equal diameter refractor, the Maksutov will none-the-less deliver very pleasing views of Saturn. I have several photographs I've taken with my ETX 90 at the ETX Astro Photos page which you can view for reference.

Schmidt Cassegrain (SCT) telescopes, like the very popular Celestron NexStar 5 SE Telescope , can also be used successfully. The SCT has a large secondary with respect to its objective, and this tends to reduce the contrast of the image. However, for the money, you can get a 5 inch SCT for much less than its comparable 4 inch refractor, and that will help make up that contrast difference. Besides, Saturn with its rings presents a fairly high contrast target, so the loss of contrast is tolerable. And most SCT users find their instruments to be very good all around telescopes as well. I recently purchased a NexStar 5SE and have observed the moon, Jupiter, and Saturn with it. It gives as good of views as I can get with any of my telescopes, including my 6 inch Newtonian reflectors.

One of my favorite telescope for planetary work is the Long Focus Newtonian. Such telescopes can be constructed or purchased cheaply compared to other similar sized instruments. The long focus Newtonian can use a smaller diagonal to reduce the loss of contrast. They also are less sensitive to alignment errors, and offer flat, coma free fields of view. The 4.25 inch f/10 Newtonian is a commonly available telescope, and makes a great planetary instrument for the small budget. Available at a good price is the Orion SkyQuest XT4.5 Dobsonian Telescope, which is an f/8 system, and makes a great planetary performer on a budget.

I use a 6 inch f/10 Stargazer Steve Newtonian. It is designed to give near refractor performance on planetary objects for a fraction of the cost of a similar sized refractor.

I special ordered my DOB, but a standard 8 inch moderate focal length DOB, like the Orion SkyQuest XT8 Dobsonian Telescope will work as about as well, and be a better star telescope.

While the telescopes listed on this web page are my preferences for getting the best planetary images, I strongly suggest that you use whatever telescope you have. Any decent telescope will let you see the beautiful ring system of Saturn.

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What Can You See On Saturn?

Above you see an illustration of the main features of Saturn that are within reach of the typical amateur astronomer telescope.

The obvious thing is of course the rings. Most telescopes of 50mm or better will show the rings and likely the ring gap -- the area between the rings and the planet itself. Depending upon the relationship between Earth, Saturn, and the Sun, you may see the planet's shadow cast on the rings as they pass behind the planet.

Moving up in size to 60mm or 70mm, you are likely to be able to see the small dark gap in the rings known as the Cassini Division. There is yet another, much smaller gap near the outer edge of the rings known as the Encke Gap, but most small telescopes will not likely see this feature.

A telescope of perhaps 6 inches or so may show the illusive inner, darker and somewhat translucent ring known as the Crepe Ring.. Depending upon where Saturn is in it's cyclic pattern around the sun, the rings may appear tipped either up or down.

On the planet itself is a light colored band around the equator of Saturn. You may also notice darkening at the poles of Saturn.

Note that the sizes of telescopes suggested for observing these features is approximate. Experienced observers can often see details through small telescopes that are only obvious to others in larger telescopes.

As Saturn goes along its decades long journey around the sun, the inclination of its rings changes. Above is an example of how Saturn may look when the rings are viewed more nearly edge on.

In fact, about every 14 to 15 years, Saturn's rings are viewed precisely edge on, and become invisible to the Earthly observer. The most recent one of these ring disappearing acts occurred in early September of 2009.

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An Xephem Presentation of Saturn

 

It's always nice to plan your observing sessions when possible. This image of Saturn and its rings was obtained with the Xephem program, and is called the xephem Saturn view. It shows a given night's approximate view of Saturn, and is particularly useful in predicting what the tilt will be in Saturn's rings.

Any roman numerals in this image refer to Saturn's moons that might be visible in this narrow field of view depiction.

 

 

This is a wider field of view depiction of the xephem Saturn view illustration. It is handy for finding out which moons of Saturn will be visible on a given night, and where they will be located.

The orientation of this view is that seen through a telescope with a star diagonal attachment. It's right side up but reversed from left to right, as in a typical refractor or Cassegrain telescope.

The labeling for Saturn's moons is shown in the following table.

Label	Name	Magnitude
I	Mimas	13
II	Enceladus	11.8
III	Tethys	10.3
IV	Dione	10.2
V	Rhea	9.8
VI	Titan	8.4

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Some Final Suggestions

There are things you can do to improve your Saturn viewing. Let your telescope cool down to ambient temperature before expecting it to deliver steady images. The time this takes is longer for bigger telescopes, and generally longer for reflector type telescopes.

Don't observe over the top of nearby buildings. The heat rising from the buildings will cause significant image instability. If possible, observe when the planet is highest in the sky, rather than low to the horizon.

Try using an eyepiece color filter, like the ones available in the Celestron 1.25 " Eyepiece Filter Set. Yellow is a common filter used to enhance the contrast of the Saturn features.