Event Date: March 17th
Time: 6:00 AM
Brief
I ended yesterday's entry about Mercury's poor morning apparition with a glaze-mention of how the planet would be seen from many southern latitudes. True, the apparition would be much better, and Mercury will have a wonderful greatest elongation. As I have a couple times, in nearly a year of working on this blog, I will pick a southern hemisphere latitude precisely equal to ours here in the northern hemisphere. Once again, I will choose Box Hill (Victoria) Australia, which is our latitude in the southern hemisphere, of 37º 49'. They are 19 hours ahead of us, if using daylight savings time. Therefore, with the change in date, I simply forwarded the clock ahead 5 hours and turned off daylight savings. Take a look at Mercury's orbit, and how the angle of the ecliptic with the horizon.
click on image to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.
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Detailed
At the date and time listed, Mercury is already rising one hour, thirty nine minutes before the Sun. On April 2nd, the rise gap is 2 hours, 18 minutes. To put that in perspective, that is bigger than the Sun and Venus sometimes, when Venus is closer to conjunction than greatest elongation. With such a gap, Mercury will be 26º in altitude at Sunrise!
Despite the southerners getting such a great apparition, let's remember another reason why, besides the excellent geometry of their morning sky at this time of year: Mercury being near aphelion. As a result, the planet doesn't brighten much until several days later, when it quickly starts moving towards conjunction. It will not be until the end of April and early May that Mercury's magnitude dramatically improves for viewers there. By then, we will start looking forward to it coming back into our evening sky. For that one, given that it will be nearly winter for the southern hemisphere, they will have a decent apparition, while we will have a fair one; the problem for us "notherners" of course, will be having to wait for the Sun to take a long time to go down, longer twilight, and Mercury eventually falling south of the Sun as it did here in the morning sky.
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