Moon – Inner Planets & 1 Star

   The waning crescent Moon, as it moves eastward toward new Phase on the 14th, passes by the two inner planets Venus and Mercury. Yesterday the Moon was west from the planets and after 24 hours of revolution the Moon has moved to between the two planets this morning.

   
   
   

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Mercury at Western Elongation – See it in the Morning Skies

   On Tuesday November 10th Mercury, the innermost planet, will reach its orbital position known as greatest western elongation at 19.1o. At that moment Mercury, the Sun, and the Earth, would be arranged in something close to approximating a right angle as this graphic shows. Even though it sounds confusing at western elongation for either Mercury or Venus the inner planet will be to the right of the Sun as we view them, meaning that at western elongation an inner planet rises in the east before the Sun rises. And at eastern elongation with the inner planet on the left side of the Sun the inner planet follows the Sun across the sky setting after the Sun sets.

   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!

   There is a lot to see and a few things you cannot see on the morning of Mercury’s western elongation. Going by relative apparent magnitudes Mercury (-0.52), Venus (-3.99), Spica (0.96), are all easily visible as bright to very bright star-like objects. The 24-day old waning crescent Moon shines at a much brighter apparent magnitude of (-11.52).

   
   
   
   
   

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Waning Crescent Moon – Venus Conjunction

   Wednesday morning October 14th in the hour or so before sunrise look eastward for the 26.8-day old thin waning crescent Moon and the inner planet Venus. Both are shining brightly with the Moon’s apparent brightness of -10.0 contrasting with the -4.0 apparent brightness of Venus.

   Both the Moon and Venus will just barely fit within the 7o field of view of binoculars with the Moon to be about 7-8o to the east, ‘below’ the inner planet Venus.


   
   
   
   
   
   
   Here is the waning crescent Moon and Venus this morning, Tuesday October 13th.

   
   
   
   
   

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Mars at 2020 Opposition

Mars at Opposition   Tuesday October 13th Mars will reach a point in its orbit around the Sun where it is at opposition relative to the Earth. At opposition The Earth is between the Sun and Mars, or for that matter, between any of the outer planets and the Sun. At opposition both the Earth and the planet at opposition will have near identical heliocentric longitude. The opposition of Mars sometimes happens around the time that Mars is at its respective perihelion, closest to the Sun. If opposition happens during or near when the Earth is at its respective aphelion, furthest from the Sun, (first few days of July) then Mars will appear larger relative to when these dates are further apart.

Where is Mars Now?

What is opposition?
orbital-positions   The outer planets reach opposition when the Earth has moved into a position with the Sun on one side and the outer planet on the other side. Because all planets orbit in the same direction (toward the east), and all follow orbits that are slightly more elliptical than circular, oppositions occur at regular intervals of about 12 months (except for Mars). Mars is considerably closer to Earth and is moving faster than the other outer planets, so it takes approximately 26 months for Earth to catch up with Mars for an opposition.

   
   
   

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Moon May Get Stung!

   Sunday morning October 11th the 23.6-day old waning crescent Moon will be about 2o from the open star cluster M-44, also known as the Beehive Cluster. This is a group of a few hundred stars located within the constellation Cancer the Crab.
click on graphic to see it larger
   Despite the large difference in apparent magnitude (Moon: -11.4 : Beehive Cluster: 3.4) The Beehive Cluster could still be visible with an optical aid or camera.

   
   
   
   
   
   
   
   
   

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Moon-Venus Conjunction + M44

   Monday morning September 14th look eastward in the pre-dawn skies for the 26-day old waning crescent Moon to be about 4-5o from the planet Venus and about the same distance from the open star cluster M-44, the Beehive Custer.

   The trio should make for an interesting view with binoculars.
   
   
   
   
   
   

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Mercury at Superior Conjunction

   Monday August 17th the innermost planet Mercury reaches superior conjunction. At superior conjunction Mercury will be on the opposite side of the Sun. The graphic to the right shows the planet positions relative to the Earth and Sun for both inner planets and outer planets.
   While at this superior 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 superior conjunction Mercury is 6.96o North and is about as far north of the ecliptic as it can get.

   Speaking about inner planets here is the other inner planet, Venus, and the 27-day old waning crescent Moon this morning.

   
   
   

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Moon – Venus Morning Conjunction

   This morning despite clouds and thunderstorms moving through the area there were enough breaks in the clouds that allowed for getting a few pictures of the waning crescent Moon and Venus.

   Following the conjunction with Venus this morning watch tomorrow, Sunday morning August 16th, for the 27-day old waning crescent Moon to have moved further east away from Venus. The Moon will be about 6-7o from the ‘Twin’ star Pollux and a few degrees further from the other ‘Twin’ star Castor.

   
   
   
   
   
   
   
   
   
   

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Moon-Venus-M35 Conjunction

   Saturday morning August 15th the thin 25-day old waning crescent Moon will be about 2-3o from the inner planet Venus, and about 3-4o from the open star cluster M-35. All three are located near the feet of the Gemini Twins.
   The contrast in apparent magnitudes is very striking with the Moon shining at -10.7 compared to the -4.3 apparent magnitude of Venus. M-35, with an apparent magnitude of 5.3 will be difficult if not impossible to see with the bright Moon and Venus nearby. Under other conditions M-35 is visible to the naked-eye under dark skies. All three rise 2-3 hours before sunrise local time and will easily fit within the field of view of binoculars. To see just Venus and M-35 wait until tomorrow after the Moon has moved further east, is a thinner crescent and less bright. However Venus will have also moved a bit more than 1o east as it orbits along.
   If you can see the crescent Moon after sunrise it may even be possible to see Venus during the daytime using the Moon as a guide for where to look.

   
   

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August Moon at Ascending Node

   Friday August 14th the thin 25-day old waning crescent Moon will be crossing the plane of the ecliptic moving north. This is known as the ascending node, one of two intersections the Moon’s orbital path has with the ecliptic. The ecliptic is actually the Earth’s orbit, and the Moon’s orbit is inclined about 6o from the ecliptic. So there are two node intersections, the ascending and descending nodes.
   On the morning of the node crossing the thin waning crescent Moon is positioned about midway between the reddish Aldebaran to the west, and the inner planet Venus to the east.
   Does our Moon actually go around the Earth as many graphics show? 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*
*Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)
   
   
   
   
   
   
   

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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