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  • Rapt in Awe

    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

Hanging around with Comet Garradd – September 2011 Event

The first three days of September offer an excellent binocular challenge that is rewarding even if you fail – and for that matter, this rewarding part can be done on any clear night in the month!

But September 1, 2, and 3 offer us a really cool opportunity to spot a faint comet as it skims past one of my favorite binocular asterisms, the Coathanger. Just learning to find the Coathanger is a reward in itself because it’s a neat cluster of stars that actually looks like it’s name implies – a coathanger.  So first we’ll give you some guidance on finding the Coathanger – then, with dark-adapted eyes in a dark sky location you can see if you can find the current interloper, a comet known as C/2009 P1 Garradd.

You can start your search for the Coathanger by locating the Summer Triangle with your naked eye. It is high overhead during an early September evening.

Face south in September in the early evening, then look high overhead. Vega is the brightest star of the three that make up the summer triangle. Identify it - then try to identify the four - much dimmer stars that make up Sagitta - the arrow. (Click image for larger version.)

As you can see, Sagitta will fit in a low-power, binocular field. It's four main stars are fourth magnitude and can be seen with the naked eye if your light pollution is not too bad and your eyes have been dark adapted about 15 minutes. Finding the charming asterism of the Coathanger requires moving just one field away in the direction shown by the arrow. Yes, the Coathanger is upside down - unless you happen to be in the Southern Hemisphere. Its brightest star is magnitude 5 and the fainter ones are magnitude six and 7 - but all should show in just about any size binocular. Click image for larger version of this chart.

Finding Comet Garradd

Comet Garradd will be visible in binoculars for several months – but it is much easier to find in the first three days of September because on those days it is passing near the Coathanger. However, it is a very faint and a challenging object for beginners who expect it to look like its pictures. It won’t. It will simply be a faint cloud. It can be seen in standard 50mm binoculars, but is much easier with larger ones, such as the inexpensive 15X70mm ones I use. Here are three charts showing its position on September 1, 2, and 3, 2011.

Click to enlarge.

Click to enlarge.

Click to enlarge.

And if you are clouded out on September 1, 2, and 3?

Don’t despair.

1. Find the Coathanger and enjoy the sight!

2. And if you want to pursue  Comet Garradd, see the chart below for its path over the entire month.

Click image for larger version. (Prepared using Starry Nights Pro screen shots. )

Finally, i strongly recommend that you go play with the controls on an orbit calculating utility at the Jet Propsulsion Lab site. This will show you how the positions of the Earth, other planets, and Comet Garradd changes with time. And if you use the slider on the side, you will see how Comet Garradd’s orbut is nothing like the orbit of the planets – how it comes in at a very steep angle and how its distance from us – and from the Sun is constantly changing.  It could be a brighter object this coming winter, for example, though then it will be in our morning sky.

Here are a couple examples of what you can see. This is what the JPL utility shows you for the Comet’s location on September 1. (This is just a screen shot – a picture – you can’t play with the settings here! For that go to JPL.)

That makes the comet appear to be very close to Earth. But it's really an illusion based on your angle of view. When you play with the slider on the right of the utility this bird's eye view turns into something like this second view.With the second view we see the comet is really coming into our solar system at a steep angle and so is "above" the earth as it appears to pass "near" us in early September, 2011.

How bright the comet appears depends on how close it is to the Sun – the utility tells us this in “AU” – Astronomical Units – which equal 93 million miles – the distance between Earth and Sun – and how close it is to Earth. However, there’s another factor impacting brightness.  A comet is like an onion with several layers to it. Sometimes one layer contains more volatile material then another layer – so sometimes a comet will brighten when it’s still quite far from the Sun, then not get any brighter even though it gets closer. So take all predictions of brightness with a grain of salt.

For more details on the past, present, and future of Comet Garrad, go here.

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