On Friday October 16th Mercury, the innermost planet, will reach its orbital position known as greatest western elongation. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows.
From our perspective the orbits of Mercury and Venus appear to move from one side of the Sun to the other – out to the left (east) from the Sun to eastern elongation, then reverse and move westward (inferior conjunction) between the Earth and the Sun to western elongation. From there the inner planet moves eastward going behind the Sun (superior conjunction) and eventually reappearing on the eastern side of the Sun for an eastern elongation. Repeat over and over – do not stop!
Both Mercury and Venus are visible in the morning skies before sunrise as this graphic shows. The orbits of both inner planets are shown where they will be on the 16th. Mercury is at western elongation while Venus will be at its western elongation 10 days later on the 26th.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.