Event Date: September 23rd
Time: 7:15 PM
Brief
As we enter autumn for the northern hemisphere, we have two planets following the setting Sun. One is too much in the glare to see, despite being somewhat-bright in apparent magnitude: Mercury (-0.7). Further out of the glare, Saturn (+0.7) sets a little over an hour after the Sun. As Mercury separates itself from our star further while Saturn moves towards conjunction, the two will become closer together. However, with Mercury sinking below the ecliptic and Saturn a couple of degrees north of it, they never come impressively, close together. By the time they will be at their closest, Saturn will become a little harder to see, getting closer to the Sun.
Here is the showing of them this evening, at 16.5º apart.
Time: 7:15 PM
Brief
As we enter autumn for the northern hemisphere, we have two planets following the setting Sun. One is too much in the glare to see, despite being somewhat-bright in apparent magnitude: Mercury (-0.7). Further out of the glare, Saturn (+0.7) sets a little over an hour after the Sun. As Mercury separates itself from our star further while Saturn moves towards conjunction, the two will become closer together. However, with Mercury sinking below the ecliptic and Saturn a couple of degrees north of it, they never come impressively, close together. By the time they will be at their closest, Saturn will become a little harder to see, getting closer to the Sun.
Here is the showing of them this evening, at 16.5º apart.
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| click on image to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp. |
Although Mercury's orbit makes it seem as if it will stay close to the ecliptic for the next week or so, that is only based on our view now. As we revolve around the Sun at our own rate, our perspective of Mercury's orbital plane gradually changes. This is the same reason that we only see it transit the Sun in May and November, when the timing is right. It isn't Mercury's orbit that is swaying up and down; it is the inclination of our orbit relative to its. With the inner planets revolving around the Sun more often than Earth, it means that if we could see the orbits, we would notice some up-and-down. Right now, since the thicker (closer) part of the orbit is lower than the thinner (further) portion, it means that we are not only looking at Mercury's plane at a sharp angle; we are also viewing it from a latitude far from the planet's equator. This last part doesn't matter for Mercury, yet it can for planets such as Saturn, which has us see its rings edge-on about every 15 years, and see the rings as if we were almost viewing it pole-down, about 7 years + a few months before and/or after every edge-on year.
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