Wednesday morning December 5th the very thin 28-day old waning crescent Moon will be within 4-5o from the innermost planet Mercury. Venus shines very brightly above or west from the Moon. About an hour after the Moon and Mercury have risen the outer planet Jupiter will rise above the eastern horizon.
Tuesday November 27th the innermost planet Mercury reaches inferior conjunction. At inferior conjunction Mercury will move between the Earth and the Sun – much like the position of the Moon at new phase. The graphic to the right shows the planet positions relative to the Earth and Sun for both inner planets and outer planets.
At this inferior conjunction Mercury will not be directly in line with the Earth and the Sun – on the ecliptic. Mercury has an orbital inclination of 7o with respect to the ecliptic. So like our Moon, Mercury during each complete orbit, will cross the plane of the ecliptic moving north (ascending node) and also moving south (descending node). For this inferior conjunction Mercury will be about 5o north from the ecliptic, approaching its maximum angle of 7o.
Our Moon reaches apogee, (greatest distance from Earth), on Wednesday November 14th. At that time the Moon will more or less be at a distance of 31.70 Earth diameters 404,341 km (251,246 miles) from the Earth.
Does our Moon actually go around the Earth? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*
On the day of the apogee the 7.5-day old waxing crescent Moon, at sunset local time (5:05 pm CST), will be over the southern horizon and joined by several planets. Just over the western horizon are the naked-eye visible planets from west to east: Jupiter, the inner planet Mercury, Saturn, and finally Mars. Neptune is shown however at 8th requires optical assistance or a camera to become visible.
Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”
Sunday evening November 11th the 3.5-day old waxing crescent Moon will be within 2-3o east (left) of the outer ringed planet Saturn. The two should look good through a wide-field eyepiece at ow magnification, and through binoculars.
Click here to go to a previous posting showing the daily position of our Moon over a 1.5 week period.
(The animated graphic is set to 1-day intervals.)
In addition to the Moon moving along in its orbit the Earth is also moving eastward along its orbit around the Sun. As the Earth revolves the sky shifts toward the west gradually moving the stars closer to the western horizon. Even the planets gradually shift toward the western horizon and out of sight.
On Tuesday November 6th Mercury, the innermost planet, will reach its orbital position known as greatest eastern 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 – from superior conjunction, behind the Sun, out to the left (east) from the Sun to eastern elongation, then reverse and move westward through (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!
Currently Mercury is visible over the western horizon at sunset local time. Joining Mercury to the right (west) is the planet Jupiter, and further east the planet Saturn, and not shown in this graphic but is there over the southeastern horizon the planet Mars. A few degrees to the left (east) from Mercury is the reddish star Antares in Scorpius the Scorpion.
Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to return to bobs-spaces.
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