Touring the Skies By: Jim Bonser (firstname.lastname@example.org)
September 7, 2012
Ps. 19:1 The heavens declare the glory of God; the skies proclaim the work of his hands. This September promises to be a great month for stargazing. The skies are beginning to get dark at an earlier hour giving us more observing time before bedtime. We have been blessed all summer with almost no mosquitoes hovering near the eyepiece and hopefully this will continue through September and October as well. So no more excuses! Take some time to get outside while the temperatures remain nice and the mosquitoes stay away! So, let’s start by going out between 9 and 9:30 and look to the western sky. I hope you have been following the two planets: Saturn and Mars as they were dancing around with Spica. Sadly, by 9 o’clock when the stars begin to peek out at the beginning of the month, Spica has already set and Mars and Saturn are so low that unless you have a really clear view of the western horizon they will be hidden by buildings and trees. The red giant star Arcturus is still high and bright in the constellation Bootes (Bow Oh tees not booties, LOL!) Remember, follow the arc of the Big Dipper’s handle away from the bowl until you come to Arcturus. As you gaze at that beautiful star, take a moment to think about how amazing that glittering orange star really is. It shines at visual magnitude -0.4. Remember, negative numbers are brighter than positive numbers – the fainter the star, the higher the number. A magnitude 6 or 7 star is about the limit for the unaided eye. A star may appear brighter to us for a couple reasons. It might be physically close to us which just like car headlights, the closer a star is to us, the brighter it will seem. Also, some stars really are brighter than others. In the case of Arcturus, it is both fairly close AND intrinsically bright. Arcturus is about 36 light years away and it shines about 110 times brighter than our sun! If the Sun and Arcturus were placed side by side in the sky at the same distance, Arcturus would appear 110 times brighter than the Sun. Brightness does not tell the whole story though, because since Arcturus is a red giant, much of its energy is given off in the infrared which we cannot see. Arcturus actually puts out over 215 times as much energy as our Sun – it’s a good thing we orbit the Sun and not Arcturus! Arcturus is about 26 times bigger than our own Sun which is about ? the size of Mercury’s orbit. If you are celebrating your 36th birthday this year, you might consider, as you’re gazing at that glittering orange-red star, that the light that you are seeing actually left Arcturus when you were born and has been traveling through space at over 186,000 miles per second ever since to finally greet you on your special day! If you turn ? turn to the left and face south, another amazing sight is waiting for you. This time it is not just one lonely star, but instead millions of them! In September, when we look to the sky in the south, we are looking toward the heart of our galaxy; the Milkyway. If the air is clear of dust and pollen and humidity, and you are in a dark area away from bright city lights, the Milkyway is just breathtaking. It stretches from the south-southwest high overhead and on to the north, where it becomes much fainter as we look out away from the core. The hundreds of thousands of far away faint stars blend together and really do look like twisted clouds against the cold black of space. The constellation Sagittarius is just above the southern horizon this time of night in September. It looks like a cowboy coffee pot, slightly tipped to the west, with the steam of the Milky Way rising out of the spout. If you now make one more ? turn and face east, our friend Pegasus, the winged horse is just clearing the treetops. The most prominent stars of Pegusus make a giant square that as it rises is tipped and standing on one of its corners. This square points to one of the most amazing objects that can be seen with the unaided eye – the Andromeda Galaxy. Andromeda is off the left (north) end of the square. It sits above three faint stars like a narrow tilted cigar. Amazing that an object as far away as another galaxy is actually visible with our eyes! Well, this is all I have room for this month. If you want to see any planets, you will have to get up before sunrise. If you do, you will see the two brightest planets, Venus and Jupiter outshining all the other stars in the sky. Jupiter is the highest of the two.
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