There’s no moon in our early evening sky this week and the only thing that may keep you from your stargazing is those pesky rain clouds.  There are, however, other clouds in our summer sky.  To find them, just find some dark sky and face east about 8:00 p.m.  If there aren’t too many rain clouds in that direction, you’ll see a band of clouds that doesn’t appear to move.  Those clouds are far beyond the reach of earthly wind.  They’re the uncountable stars of our galactic home, the Milky Way.  

If you’re facing east, look to your right and you’ll see a giant fishhook.  That’s the tail of Scorpius the Scorpion.  The center of our galaxy is between the hook in the Scorpion’s tail and the spout of the teapot in Sagittarius.  If you have binoculars, you'll see an amazing number of stars in this area.  Your binoculars are much better optical instruments than Galileo’s crude telescope.  In 1610, he discovered the true nature of that sky river just as you can tonight.  But there’s even more wonder connected with the Milky Way.

Though you feel absolutely stationary as you lie in your lounge chair gazing up at that lovely sky, you’re actually rushing several different places at once at incredible speed.  If you contemplate the starry wonders for more than a few minutes, you’ll notice that they rise higher in the eastern sky.  If you find a star near the eastern horizon and look at it later, you will see that it’s higher in the sky.  The star isn’t moving; you are, at 1006 mph as the Earth turns.

Now, look at your watch and note the exact time.  Then, look at the Scorpion’s tail and notice where it is in relation to the horizon or a coconut tree or some other landmark.  Then in a couple of weeks or so, go back to the same spot at the same time and look for the Scorpion’s tail.  You won't find it in the same place because your view of the heavens has shifted.  Earth, the giant spaceship we all ride, has traveled to a different place in its orbit.  As you sit there in your lounge chair, you’re traveling at 66,000 mph as the Earth goes around the Sun.  Spaceship Earth travels significantly faster than most of the spaceships we’ve launched into space.  As you absorb that incredible speed, you should also realize that you’re riding a much larger merry-go-round than that one as you sit relaxing in your lounge chair.

Our galaxy is huge; so big that it’s hard to grasp the size.  Like all spiral galaxies, the Milky Way is a flatted disc of stars.  It’s about 100 light years thick out here in the galactic suburbs and it’s about 100,000 light years across.  The proportions are not unlike that of a CD with a slightly bulging center.  The Sun is located about halfway out on one of the spiral arms and the galactic center; there off the teapot’s spout is about 25,000 light years away.  

The Earth orbits the Sun because it has to; if it didn’t endlessly fall around the Sun, the Sun’s gravity would pull it in.  The same is true of the Sun.  Our Sun and all the other stars in the galaxy endlessly fall around the galactic center.  The closer you are to a gravity mass, the faster you must go.  Mercury orbits the Sun at over 100,000-mph and stars close to the galactic center must whirl around it at incredible speed.  But hey, we’re way out here in the suburbs so how fast can the Sun go?  The Sun orbits the galactic center at almost 500,000 mph and we’re all along for the ride.  Enjoy your amazing cosmos this week.  
 
 

Would you like to be on the Planetarium e-mail list and receive a monthly reminder of the Planetarium shows and occasional notices of cool things in the sky?  Just send an e-mail to stars@guam.net requesting that you be added and I'll put you on the list!

Don't forget that you can hear this information on Guam's public radio station KPRG, 89.3 on your radio dial.  The program is called Tropical Skies and it airs twice on Monday, during the noon hour at 12:25 and at 6:01 in the evening.  Support your public radio station

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