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Today’s chart is aimed toward the galaxy’s center, which is located some 30,000 light-years away. Remember, when you are looking at this starlit band across the sky – visible from country locations – you are peering edgewise into our own galaxy.
Today’s chart shows that the starlit trail of the Milky Way seems to bulge just before it reaches the southern horizon. This bulge marks the approximate location of the Milky Way’s center. This part of the Milky Way is vastly more spectacular in a dark night sky than it appears here on our chart! The constellations Sagittarius and Scorpius lie in this direction as well.
Because of its faster speed and shorter distance to go around its orbit, our Earth laps Jupiter about once every 13 months. It’s a lot like a fast race car in the inner track passing a slower car in the outer track. The race car analogy works well to explain a phenomenon called “retrograde motion.” Normally, an observer in the inner, faster race car (Earth) would see the slower, outer race car (Jupiter) appear to move forward (prograde motion). But as the inner car begins to approach the slower outer car before it passes it, the outer car appears to slow down as viewed against the stellar background. This is purely geometric illusion since the outer car does not actually slow down. But the outer car appears to slow down and just before the inner car passes it, it apparently reverses motion and travels backward against the “fixed” stars. Again, this is purely a geometric illusion. In astronomy, this is called “retrograde motion” and that is what Jupiter appears to start doing starting today. Technically, the moment that the planet appears to change its direction of motion is called the “stationary” point.
Right now Jupiter is in the eastern sky at middle to late evening. It’s rather high in your southern sky by daybreak. For the next several months Jupiter will appear to drift slowly westward among the stars of the constellation Aries the Ram. Because of their true motions, Jupiter and the other outer planets normally drift slowly eastward against the background of the stars. However, during this time (which ends on December 26), Jupiter appears slightly farther to the west each night. You can’t tell this from night to night with just your eyes, but if you note Jupiter’s position relative to some nearby stars, you should be able to notice it over a period of a few weeks. On the up side, Jupiter is very easy to identify – just face east at late evening tonight and look for he brightest object in the sky.