Monday January 18th the innermost planet Mercury will reach its greatest angle above the ecliptic at 7o North. The plane of the ecliptic, or the Earth’s orbital path around the Sun, is the reference ‘line’ for measuring each planet’s respective orbital path angle from. This is known as inclination and Earth’s has an inclination of 0o while Mercury has an inclination of 7o.
Mercury was recently at inferior conjunction, between the Earth and Sun (like a new Moon phase) but due to the 7o inclination for Mercury’s orbit it was not directly between the Earth and Sun on the ecliptic. This inclination of Mercury’s orbit, like the Moon’s 6o inclination from the Ecliptic, means that not every new Moon or inferior conjunction of Mercury results in either a solar eclipse or a Mercury transit.
As Mercury and the Earth continue revolving around the Sun the angular difference between the two orbits will change as Mercury’s orbit criss crosses the ecliptic in its regular pattern of ascending and descending nodes. Keep track of these as on May 9th, at descending node, Mercury will transit, cross the disk of the Sun in a Mercury transit.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.