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Wednesday, May 4, 2016

Planets are pairing up

Thursday, March 8, 2012

If you have been watching the evening sky, as I hope you have, Venus and Jupiter are moving closer to each other by the day. During the next week they will have their closest approach of the year. They won't be this close again until March of 2023, so go out an look at it now.

The official date for the closest approach of the planetary pair is Tuesday, March 13. On that date they will only be three degrees apart. That is about the width of six full moons.

If you miss the Tuesday conjunction, or it is cloudy don't worry. They will still be close on Wednesday evening. But really, any evening between now and then and even extending for another couple of days beyond will show a close meeting of these two planets. A great sight in binoculars.

When you are out viewing the planetary pair, turn around and look east for another planet, bright, orange, close Mars. Mars was at opposition, opposite the Sun in the sky, on March 3, but it will be bright and easy to observe for a long time yet.

Now, I promised to talk about retrograde planetary movement. Because Earth rotates on its axis, the stars appear to move from east to west just as the sun does. However, the outer planets -- those planets further from the sun than Earth -- appear to have a different motion.

The normal observed direction of the outer planets' motion against the background of the stars is from west to east. Occasionally, when Earth overtakes an outer planet and passes it, the outer planet's motion -- direct motion -- appears to reverse itself and change to a motion of east to west.

This reversal is called retrograde motion. This is a good time to discuss this topic because right now Mars is in retrograde motion. If Mars is observed over a period of time, night to night, it will appear to move toward the west.

If you start observing now, while Mars is high and bright in the east after sunset it will appear to be moving toward the bright star Regulus in Leo the Lion. Regulus is the star at the bottom of the backward question mark that it the lion's head and mane.

It is the same principle that makes a car you are passing on the highway appear to travel backward against the distant background. In reality both cars are going the same direction, it is just that one appears to go backwards.

If you keep watching, Mars will approach Regulus and will arrive at its closest point on the evening of April 14, 15, and 16. At which time it will reverse its apparent direction of travel back to the normal, direct motion, of west to east.

On Aug. 13, Mars will be near Saturn (further east). In October it will be near Antares in Scorpius, and in February of next year a grand triple-conjunction with Mars, Neptune, and Mercury.

This is the reason to keep looking each night, there is always something different to see.

SKY WATCH: Full moon, Thursday, March 8. Venus and Jupiter are still close. So are Mercury and Uranus and will be in the same binocular field of view for a few more days but both will be too close to the sun for observation by the end of this week. It will officially be spring on Monday, March 19. Now, I know the calendar says Tuesday, March 20, but the official time for the Sun to cross the equator heading north is 1:14am EDT on Tuesday. Now if we check out our timezone map we see that 1:14am EDT is 11:14pm MDT. Hence, spring starts for us on Monday. PS: Did you notice the "Daylight" time designation? Yep, it's back. Daylight Savings Time starts at 2 a.m., Sunday, March, 11. This time we "Spring" ahead and lose an hour of sleep.

NEXT WEEK: More astronomical blathering.

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Vernon Whetstone
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