Click on graphic to see it full size.
Mercury reaches a point in its orbit called greatest eastern elongation
. As this graphic shows the inner planet Mercury is more or less at a right angle (90o
) from the Sun and Earth. From the surface of the Earth, your backyard, for example, Mercury is to the left, or eastern side of the Sun and is setting after the Sun.
At eastern elongation Mercury, or for that matter Venus the other inner planet, are as far out from the Sun as we see them and as a result Mercury or Venus will set at the latest time in this orbit. From eastern elongation forward Mercury or Venus will be setting earlier each evening as the planet is moving in retrograde, westward, toward the Sun and inferior conjunction. With luck and a clear horizon the very thin waxing crescent Moon
, approximately 30 or so hours old, may be just visible to the right from Mercury.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.