Event Date: August 30th
Time: 6:15 AM
Brief
As Mercury approaches superior conjunction, the geometry of the eastern sky has been favorable enough to let us see it at a very bright magnitude, while still separated enough from the Sun. The planet (mag -1.3) still rises a little more than 50 minutes before our star, and just slightly dimmer than our brightest star Sirius (-1.5) when seen with the eye. To some viewers, the two will look the same brightness, although Mercury will not twinkle; more of that in the detailed section. Before that, I will show Mercury, Sirius, Venus and Jupiter. Notice how the triangle shape of Sirius, Venus and Jupiter continues to become more impressive as Venus pulls away from Jupiter more quickly each morning.
Time: 6:15 AM
Brief
As Mercury approaches superior conjunction, the geometry of the eastern sky has been favorable enough to let us see it at a very bright magnitude, while still separated enough from the Sun. The planet (mag -1.3) still rises a little more than 50 minutes before our star, and just slightly dimmer than our brightest star Sirius (-1.5) when seen with the eye. To some viewers, the two will look the same brightness, although Mercury will not twinkle; more of that in the detailed section. Before that, I will show Mercury, Sirius, Venus and Jupiter. Notice how the triangle shape of Sirius, Venus and Jupiter continues to become more impressive as Venus pulls away from Jupiter more quickly each morning.
Detailed
Seen further south (right) of Mercury when looking at the image below is Sirius, much better placed for viewing pre-Sunrise, than it was at the beginning of the month in the glare of dawn. While at that time, Sirius and the Sun only about a half-hour apart rising, Sirius now rises about two and a half hours earlier than the Sun. During nautical twilight, observe it sparkle many colors as its light is refracted through the atmosphere. The cycle of colors is quite fast, so try doing so with a telescope out of focus to notice the range of rainbow-like ones.
Getting back to Mercury, as a review, it does not make its own light as Sirius does, but a big enough gibbous shape now to reflect alot of it from the Sun to our eyes. Less than a week past perihelion, Mercury is a little closer to us than it would be at aphelion and therefore, the aforementioned Sirius-like magnification. Jupiter, at about 70 minutes before transit, and Venus lower down, are seen much brighter in the sky. Both are higher than Mercury, and rise before astronomical twilight. As I mentioned with Mercury, Venus is getting help from the sky's geometry as well, rising over 3 1/2 hours after the Sun. It is past greatest elongation, but far enough north of the Sun to be very well placed at this time of morning: a little more than 36º in altitude.
Finally, look below Mercury in the image, at Regulus (mag. +1.3), barely visible in atmospheric pollution and Sun glare. Mercury is being several times brighter, so let it guide us to the "Lion-star".
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