Saturday October 20th is International Observe the Moon Night. That evening the 12-day old waxing gibbous Moon rises around 5 pm local time and will be over the southeast horizon during the evening hours. Joining the Moon are several planets – all located to the west, right, from the Moon. Early, shortly after sunset the inner planet Mercury will be just above the western horizon. Moving east from Mercury is Jupiter, then Saturn, then Mars. The planet Neptune is only a few degrees above the Moon but because of the Moon’s reflected light Neptune will not be visible.
Our Moon reaches perigee, (closest distance to Earth), for this orbit on Saturday September 8th. At that time the Moon will be at a distance of 28.325 Earth diameters (361,355 km or 224,535 miles) from the Earth.
Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”
Early mornings this week, before the local time of sunrise, look toward the east for the innermost planet Mercury as it moves east passing within about 1-2o from the star Regulus. This animated graphic shows the morning skies on September 5th to the 7th at 5:15 am CDT
Regulus marks the bottom of the backward question shape for Leo the Lion, and Regulus also represents the heart of Leo.
Wednesday August 8th 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 7o south, its maximum latitude south from of the ecliptic.
This is one of those ‘best of times’ with regard to planet viewing. All of the visible planets are above the horizon although Mercury sets just before Mars rises. Times like this make it easy to visualize the ecliptic and its relationship with the planets. And our Moon, as it waxes toward full phase over the next several days, will pass by several planets and dwarf planets.
Click on a graphic to start a slide show.
The three, Moon, Venus, and Regulus, all fit comfortably within a binocular field of view.
On Thursday July 12th 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 are the planets Venus, Jupiter, and Saturn. Mars rises about an hour after Mercury sets.
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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