Thursday, April 30, 2015

We Interrupt this Coverage to Bring You Current Events!

While I should be continuing to catch you up on our excellent astronomy adventure from last week, current events are stepping in to interrupt! Currently in the western sky, the planet Mercury is in conjunction with the Pleiades Star Cluster! I've alerted local observers to it, so hope you have been watching - it is really pretty in binoculars.

Of course, all these alignments of solar system objects are from our vantage point on the Earth.n In reality, the innermost planet Mercury is not physically close to the Pleiades, just from our perspective from our planet. But still, it is fun to observe and watch the day-to-day movements. Of course, everything in the sky appears to spin over our head every 24 hours because of the earths rotation on its axis. In addition, the Pleiades, as do all stars near the ecliptic path which the Sun follows, appear to move slowly from east to west about 4 minutes of time (about 1 degree) due to the Earth's motion in its orbit. In another couple weeks, the star cluster will be invisible as it will appear to move behind the Sun, to pop out in the morning sky in a few months... Mercury, on the other hand, is coming around the far side of the Sun, higher into our evening sky a little more each night. Shown at left was Mercury and Pleiades from last night, Wednesday, 29 April. The image is cropped from seven exposures with a 200mm lens, about 45 seconds total exposure, tracked with a Polarie tracking mount. Mercury is the bright object at lower left, the cluster at upper right. Since Mercury never gets very far from the sun, the shots were taken in twilight, the cause of the glow - not light pollution, man-made at least!

Tonight is the closest approach of the pair, so went out again to capture them. There were some thin clouds, and one shot had an airliner go thru (not used for the stack). But they were significantly closer, easily fitting in a binocular field. This set of 12 exposures totaled 110 seconds of exposure.

Interestingly, today Mercury was in the news because the Messenger space probe, which has been orbiting Mercury the last 4 years, was purposely crashed onto the surface after running out of maneuvering fuel.

The planet continues to draw away from the Sun, getting higher in our sky, but will also be moving further from the Pleiades. Greatest elongation from the Sun will be on 6 May, after which it will slowly move back closer to our star, passing inferior conjunction (between us and the Sun) in a month on 30 May. Get out and observe the rarest of the naked-eye planets, and do search for the Pleiades to the lower right of it if you check the next day or two!

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