Planetary triangle, 8/6/2010

For previous nights see these entries:

Planetary line-up at sunset (Introduction, with Jack Horkheimer videos)
Planetary triangle, 7/29/2010
Planetary triangle, 7/30/2010
Planetary triangle, 7/31/2010
Planetary triangle, 8/5/2010

So. Through a series of adventures that included not buying a corded electric weed-whacker, going to the wake of a father of a long-lost friend in Scranton, discovering upon leaving the wake that one of my tires was completely flat, reinflating that tire and hoping it would hold air until I got back to Nanticoke (a distance of some thirty miles), and then not buying a new seal for the flush mechanism of a slow-filling toilet, I found myself back in Nanticoke on the clearest night in a week with only minutes to go before Venus would pass out of visibility. I leaped out of my car with my tripod and camera and quickly realized that the only clear vantage point would be, once again, on the sidewalk along one of the busiest (if not the busiest) streets in the city.

I set up and tried to position myself so that Mars and Saturn would not be obscured by overhead wires. I got lucky right off the bat and got this image at 9:14 PM. (As always, click to get a larger image.)


I then proceeded to take image after image, thirteen in all. This was the sixth, taken at 9:16 PM:


My final shot of the night has Venus just passing behind a rooftop at 9:18 PM. Unfortunately there was no other vantage point that had an unobstructed view of the planets, so I had to call it a night at that point - scaring the heck out of some people walking their dog along a cross street. Having a large man dressed in black pants, white shirt, maroon tie, and black suspenders suddenly come across a lawn toward you while toting a camera tripod with a camera the size of a deck of cards attached is always surprising.


I realized that all of my images were essentially identical, so it should be possible to do a time-lapse study like I did with yesterday's images. Unfortunately it became clear quite quickly that my pan head had shifted slightly between some of the photos, especially between the third and the fourth and by a much smaller amount between the eighth and ninth. I removed the first three images from the sequence and worked with the rest.


Two background stars are visible in this photo that were also visible in yesterday's three-image sequence. One dim star is just above and to the right of Mars. (In the image below this almost looks like an image artifact, but trust me, it's really there.) According to Google Sky, this is Eta Virginis - apparent magnitude +3.9. Not bad for my little camera! Another, brighter star can be seen trailing well behind Mars. This is the binary star Gamma Virginis - combined apparent magnitude of +2.9. (Or +2.74, take your pick. Wikipedia lists both.)


It seems like it was just last Saturday that I was noting the presence of Beta Virginis midway between Venus and a line drawn connecting Mars and Saturn. But that was then, and this is now. Beta Virginis is now located on the other side of Venus, heading towards the sunset twilight. While these planets appear somewhat lower each day, they are all moving against the background stars in a direction opposite the nightly direction of the background stars. This motion has more to do with the motion of the Earth in its orbit than the actual motion of the other planets in theirs.

Imagine a series of concentric merry-go-rounds, with the Sun the calliope in the center. Mercury rides the first merry-go-round out, Venus the second, Earth the third, Mars the fourth, and Saturn the sixth. (Jupiter is on the fifth merry-go-round, but it's behind us.) Oh, and each merry-go-round out moves slower and slower, though they all sweep out equal areas in equal times. Right now we can see Venus (which is closer to the center than we are), and Mars, and distant Saturn. It appears that Saturn has moved dramatically over the nights I've been photographing it, but in fact it's moved very little. Mars and Venus and Earth have all been moving more quickly, and the relative positions of Venus and Mars and Saturn also appear to be shifting because of the motion of Earth. Meanwhile, the background stars can be thought of as the stands and buildings outside the last concentric merry-go-round (on which poor, forlorn Pluto rides - well, actually, there are merry-go-rounds beyond that...). Or maybe we can think of them as distant mountains. Whatever they are, they appear to swing by dramatically, when in fact they are not moving at all. Wait, yes they are. Oh, and our calliope is moving, too, and dragging all its concentric merry-go-rounds with it.

My point is: thinking about all this stuff will make you feel vertiginous. And don't get me started on retrograde motion.

On Sunday these three planets will be in their tightest configuration of this conjunction. By next Thursday and Friday nights the planets will be pulling apart in the sky, but the thin crescent Moon will join them on those nights. Let's hope for clear skies!