Saturn remains a stargazer’s delight for June nights

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Saturn during April and May was the closest, biggest and brightest it will be during 2013. And it will still be a great view in June.

The ringed planet is the most distant one visible with the naked eye. The unit we use to measure distances in the solar system is the astronomical unit (au), which is the average distance between the Earth and the sun. The Earth on average is 1 au from the sun, whereas Saturn is 9.8 au, a distance that takes light 1.36 hours to travel.

In June, Saturn is 1.24 light hours from Earth, meaning that if you’re looking at Saturn at any time during the month you’re seeing it as it was 1.24 hours previously.

If you have a chance, this is also a good time to view Saturn’s ring system through a telescope. The rings are now tilted about 18 degrees from our line of sight, the widest it’s been since 2006. The tilt will continue to increase until 2017, when it reaches its maximum of 27 degrees.

Also, with a moderate telescope you can see six or seven of Saturn’s 60 known moons.

And now the big question: If I go out on a clear night in June, how do I find Saturn in the sky?

One answer is to look at right ascension 14 hours 19 minutes and declination minus 11 degrees 7 minutes. That is not much help for most backyard stargazers.

It may be more helpful if you are told to look in the eastern part of the constellation Virgo, but that will only help if you know where Virgo is.

I think the best way to answer the question is to use a star chart.

The most useful charts for stargazing show the overhead sky as a circle with the horizon at the edges. The cardinal directions of north, south, east and west are labeled on the edges. The stars, planets and other stellar objects are symbols inside the circle, with their positions representing their locations in the sky.

To use the chart, you hold it overhead with the cardinal directions on the chart orientated to match those at your location. You can then match up the stars on the chart with the ones you see in the sky.

However, you must have the right chart for the time and location of your observation. There are three factors that determine the chart you should use: your latitude, the date, and the time of night.

Your latitude determines the north/south position of the stars you can see. As you move north, the visible stars will appear to move to the south, with more stars appearing in the north as the southernmost stars disappear below the horizon. The opposite is true if you move south.

The date is important because that determines where the Earth is in its orbit. At a given time from night to night, the position of the stars will appear to move to the west. Each star will rise earlier in the east and set earlier in the west.

The time of night is also important. Because of the Earth’s rotation, during any given night the stars will appear to move slowly to the west

Where can you find the right chart?

One good source is in an astronomy magazine. Both Astronomy and Sky & Telescope print general star charts in each monthly issue. (The Walla Walla Public Library has a subscription to Astronomy, Walla Walla University’s library has Sky & Telescope and Whitman College’s library has both.)

These published charts are for the month of the issue and will state their local time of night. They are for latitudes south of Walla Walla, so they will not exactly match our sky. Although you will have to make adjustments for latitude, date and time, these charts are a good enough guide to help you find most objects in the night sky, including Saturn in June.

If you have a smart phone or tablet, you can also access some great star chart apps. I have several on my iPhone, such as Star Walk and GoSkyWatch. On my Nexus tablet (an Android device), I use apps like SkEye and Google Sky Map.

If you are using a star chart app on any device with internal GPS and compass, the device knows your location and the local time and date. This means the apps can produce real time star charts for your location with no adjustments necessary.

Most of these apps therefore have what I call “point and look” — if you point the device at the night sky it will display a star chart for that part of the sky. And as you move it around the sky, the chart will change to match the portion of the sky at which you’re aiming. These apps are a great way to find Saturn in June.

So here’s your assignment for June: Use a star chart to find Saturn on as many clear nights as you can. If you look at about the same time each night, you will notice that it is moving a little to the west. During each night it will also move slowly to the west.

Hint: At dusk during June, Saturn is about due south, nearly 45 degrees above the horizon between the bright stars Arcturus and Spica. The moon will pass just below Saturn on June 18 and 19.

Marty Scott is the astronomy instructor at Walla Walla University, and also builds telescopes and works with computer simulations. He can be reached at marty.scott@wallawalla.edu.

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