June 1: Deep sky visual observing

Would you like to improve and challenge your visual observing skills? Our June 1 meeting will focus on techniques and practical aspects of deep sky observing;  locating celestial showcase objects and so forth.
The public is welcome to this and all monthly BMAA meetings; you don’t need to be a member to attend. The meeting starts at 7:30 PM at Upper Dublin Lutheran Church, 411 Susquehanna Road, Ambler, PA 19002 (About ¼ mile from the Butler pike exit of the 309 Expressway). Look for the yellow and black BMAA signs.

Saturn will be as big as the Moon on June 1st 2016. . . . . . . . . . . . Don’t miss it!

saturn-6-24-2014 Lee Zager

Image by Lee Zager

This headline has crossed my inbox a few times in recent weeks from folks excited to see Saturn suddenly fill up our nighttime sky. People wonder why we’re not planning major observing events around this momentous occasion. Well the truth is, if you are on social media – you have been a victim of “viral click-bait”. Those attention grabbing headlines and graphic pictures entice you to click on a link which is basically for the benefit of the wallet of a website that receives revenue from people visiting their site. It doesn’t cost you anything except wasted time, but the website receives money for all the eyeballs seeing the advertising on their site. Most of these are clever in that they suck you in and force you to click on multiple pages with a little piece of the story and more advertising every time you click to see more of the bogus story.

If Nancy Regan was alive today she just might say “Just don’t click”. I usually look at who or what is sending it. Since astronomy is my passion, I know most of the credible sites. If NASA/JPL, Sky & Telescope and Universe Today aren’t sounding the alarms, you can be pretty sure the whole Saturn filling our sky is well, a non-event.

With that said, this is a teachable moment on many fronts. Undeniably, Saturn is the jewel of our solar system. If it is in the sky, I always want to see the ringed beauty hanging out in the inky darkness almost a billion miles away. So let’s talk about Saturn and the reality of the 2016 showing. This will be a little orbital mechanics and explanation of size in respect to time and space. We’ll throw out some numbers, but won’t get heavy into the math involved.

Where is Saturn right now?

Saturn is always “out there”, it is just that as we orbit the Sun our the view of the night sky changes seasonally. This is a gradual change of about 1 new degree of sky revealed with each passing day. In addition to that motion, Earth rotates on its axis once a day creating the apparent motion of the Sun, stars and everything else moving throughout the day and night. This is why things rise in the east (northern hemisphere) and set in the west. The combined effect of these two motions creates the ever changing scene above our heads. This is why we see certain things at certain times of the year. Right now (late spring 2016), we’re coming into that part of the night sky where Saturn has been waiting for us to see him.

Earth orbits the Sun in a year, Saturn being so far away takes 29.5 years to make the same trip around the Sun. I’ve gone around the Sun 61 times; Saturn has made that trip twice in that same time frame. It’s way out there! During the course of “our” year, we vary our distance to Saturn between 746 million miles when we are in our orbit closest to it (called opposition) and almost a billion miles when we are farthest away. To us, Saturn only changes about 12 degrees from when we saw it about a year ago. If you hold your fist at arm’s length up where Saturn is now, it will only move about the width of your fist to the east next year at this time. The outer planets move slow against the background of stars.

Another way to gauge it’s distance, is in terms of Astronomical Units. This is a form of measurement that works best with solar system objects. The distance from the Sun to Earth is 1 Astronomical Unit or A.U. (in miles that is about 93 million miles). Saturn is 9.5 A.U. From the Sun. Light from the Sun reaches Earth in about 8 minutes To Saturn increase that to about an hour and 14 minutes – and that is at light speed!

How big is Saturn?

Planet Comparisons     It is huge compared to Earth. Earth’s diameter is about 7,926 miles at the equator. Saturn checks in at 72,367 miles across. But if we include the rings, it swells to 186,411 miles across. But because of its distance it appears quite small in the sky. How small? We tend to measure things in the sky in terms of degrees and fractions of a degree. For this purpose we disregard the distance factor and think of the sky as being displayed on a celestial sphere. So, yes things have different brightness levels and size. Clearly some stars are brighter and dimmer and the Moon is much larger looking than the stars and planets. So we measure those diameters and distances between objects on this sphere in terms of how many degrees apart things are. In Geometry we measure things with a protractor expressing those angles in degrees. So if we think of the entire sky (night and daytime skies) as a sphere with 360 degrees to go around once. Where we stand on Earth we can never see all 360 degrees at once. (over the course of a year, we do). So for simplification purposes lets say we see 180 degrees from horizon to horizon, If I put the zero point on the eastern horizon, and measure all the way to the western horizon it would be 180 degrees. Directly overhead would be 90 degrees (astronomers call this the zenith point). Half way between the horizon and directly overhead would be 45 degrees. So we can express arcs across the sky between things in how many degrees apart they appear. This is very useful to astronomers when navigating around the sky to find their targets. Often we say “such and such” is so many degrees above the horizon or 10 degrees west of a certain star.

OK, let’s make this even more practical, your pinky finger held up against the sky at arm’s length covers about 1 degree of space. The Sun and Moon occupy 1/2 of a degree (yes, I know it’s hard to believe a rising full Moon is that small – but it’s true). Once we drop below a full degree we divide the degree into 60 arc minutes. If what we are looking at is smaller than that, each arc minutes is farther subdivided into 60 arc seconds. Think of it like how we divide an hour into 60 minutes and then a minute into 60 seconds, except instead of time we’re talking about a distance across the sky.

So we said the Moon is 1/2 of a degree, or 30 arc minutes across. Saturn when it is at its closest approach to Earth will cover only about 18.4 arc seconds of the sky – that’s pretty tiny when you look up into the sky. Nowhere even near the size of the full Moon. If you were comparing it to the full Moon, it would only be about 1/100 the Moon’s width.

Rings?

The beautiful rings are certainly what sets Saturn apart from the other planets we look at. Although some other planets have rings too, most are too dim for amateur telescopes to detect. There are several theories about why Saturn has rings. From the analysis of reflected light, we know they are for the most part ice and small rocks. A few chunks being perhaps as large as a school bus, but most are very small. Scientists think these are the remains of an icy body that was moon which broke apart from the tremendous gravity on Saturn. Some think it was a moon which never formed or perhaps even a “captured” moon pulled in close to Saturn and then ripped apart from the strong gravity. Either way, they are stunning in a small telescope. Another astounding fact is that the rings although wide are not very thick, only about 30 feet!

Saturn ring tilt NASA     If you follow Saturn over the years you will notice that the angle of the ring’s tilt changes. Due to the tilt of Saturn on its axis and how it revolves around the Sun our perspective view changes on how we see the rings. This year, we are in for a treat. The rings are opened up as wide as we ever see them, about 27 degrees. This gives us a great view of the details in the rings. Over the next 7 and a half years the rings will gradually close down. In the middle of 2023, they will appear “edge on” again to Earth. For a few weeks they will practically disappear in a thin line. Although some people will be disappointed that year, this is a rare treat that only happens about every 15 years. I witnessed this phenomena in 2008, and it was a memorable event in my observing history.

Galileo Saturn 1610

Galileo’s sketch of Saturn in 1610

The rings were first noticed in 1610 by Galileo. Due to his small and primitive telescope they looked like Mickey Mouse “ears” on either side of the planet. This was something incredibly unusual in a Universe of perfectly spherical worlds (at least that is what the astronomers, astrologers and religious leaders at the time thought they should be). He did not know what the ears were really rings. A few years later in 1612 Galileo noted the disappearance of the ears. “I do not know what to say in a case so surprising, so unlooked for and so novel.” It was not until 1655 that the astronomer Christian Huygens correctly described them as a disk surrounding Saturn.

Many astronomers mark their first sight of Saturn’s rings in their telescopes as a life changing moment.

How and when can I see Saturn?

Saturn is one of the 5 planets we can see with the naked eye in the night sky. If you know where to look it stands out looking like a bright yellowish star. Saturn like most of the other planets, rides along the ecliptic path in the sky. The ecliptic runs in an arc generally from east to west. Depending on the time of year this may be higher or lower, but occupies the southern part of the sky in its path from horizon to horizon.

To locate you will need a chart or map of the night sky. One place to obtain a free one is through www.skymaps.com. Here you can print out monthly sky maps that show the main stars, constellations and position of available planets. They also show the position of the ecliptic line. Other sources include apps that you can download to smartphones and tablets that also show the same data. The secret to finding the planets is to recognize what constellation they are in at the moment. Easier said than done, for people just starting out exploring the night sky. This is where coming out to a star watch will be a big help in locating the plants among the stars. Another distinguishing feature to look for is that planets tend not to twinkle like the surrounding stars. So looking for that non-twinkling yellowish bright object will help you pinpoint Saturn. Since the Moon also rides somewhat along the ecliptic, too, there is usually one evening a month when it might be fairly close to Saturn. Again your star map or app can show you which night will be best.

Screenshot_2016-05-22-15-46-30Right now Saturn is in the constellation Ophiuchus. What? Never heard of Ophiuchus? Don’t worry you are not alone. There are 88 constellations in our sky sphere (this includes the southern hemisphere). Most people only know some of the well-known constellations or asterisms (star patterns which look like something familiar, such as the big dipper, which is part of the constellation Ursa Major or “Big Bear”). But an easier way to hopefully find Saturn is to look for the constellation Scorpius or Scorpion in the southern sky in early evening. This constellation with some imagination, actually does resemble the shape of a scorpion. It also looks like a big “J” shape in the sky. The prominent star in the scorpion is a reddish one called Antares. Scorpius also has another transitory visitor this season, Mars. Right now Mars is quite prominent as it too is relatively close to Earth and has a distinctive reddish/orange color to it (non-twinkling, also). Mars, Saturn and Antares will stand out in that part of the sky. If we use our outstretched closed fist as a handy measurement tool, you should be able to cover all three objects within that space. Saturn is close to Scorpius and Scorpius is easier to identify than Ophiuchus. Saturn is 28 degrees above the horizon (3 fists) and almost due south.

Once you have identified Saturn, it’s not going anywhere fast. So you will be able to easily see all throughout the summer of 2016. To see the rings you will need a small telescope. A 3″ telescope will definitely show them. A 6″ telescope should also bring out more details in the rings themselves. If you don’t have a telescope go out to a star watch with your local astronomy club. We have a calendar on the Bucks-Mont Astronomical Association website and often post star watch information on our Facebook page.

Seeing Saturn “live” through a telescope is usually a moving experience. Especially if you can appreciate the back round information in this article. That pinpoint of light penetrating our atmosphere, coming directly down the telescope to your eye from almost a billion miles away really helps shape our place in this vast universe. I hope you will join us on one of these warm summer nights to enjoy it,

Keep tabs on all things astronomical by visiting our website http://www.bma2.org or like and follow us on Facebook – no bogus clickbait, we promise!