Mercury at Western Elongation

   On Friday August 9th Mercury, the innermost planet, will reach its orbital position known as greatest western elongation at 19.0o. 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!

   Mercury is visible in the morning skies about an hour before sunrise local time, as this graphic shows.

   
   
   
   
   

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Mercury at Inferior Conjunction

   Sunday July 21st 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 south of the ecliptic, but angling north approaching its ascending node toward the middle of next month.

   
   
   

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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July Perigee Moon and A Conjunction with Regulus

   Our Moon reaches perigee, (closest distance to Earth), for this orbit, on Friday July 5th. At that time the Moon will be at a distance of 28.51 Earth diameters, 226,011 miles (363,729 km) from the Earth.

   The 4.50-day old waxing crescent Moon is over the southwestern horizon at sunset local time and sets around midnight. About 1o east from the Moon is the ‘Heart of the Lion’, the star Regulus in Leo the Lion. The two will easily fit within the field of view of binoculars or a low power telescope eyepiece.
   Appearing lower above the western horizon are the planets Mars and Mercury.

   Does our Moon actually go around the Earth as this graphic shows? 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)

   Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.


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Waxing Crescent Moon on the Move

   Shortly after sunset local time on July 3rd look toward the western horizon for the 1.5-day old thin waxing crescent Moon to be close to the planets Mars and Mercury, and within about 4-5o from Pollux, one of the Gemini Twins stars.
   The following evening, July 4th, the 2.5-day old waxing crescent Moon will have moved about 15o further toward the east and will be about 3-4o from the open star cluster, M-44. Also known as the ‘Beehive Cluster’ it is a group of stars around 600 light years away and visible to the naked eye as a small ‘smudge’ of light with an apparent magnitude of around 3.70.
   Both the Moon and M-44 will easily fit within the field of view of binoculars.

   
   
   

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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July Moon at Ascending Node

   Wednesday July 3rd the 1.5-day old waxing crescent Moon will be crossing the plane of the ecliptic moving north relative to the ecliptic. 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 day of the node crossing the thin waxing crescent Moon will be close to the planets Mars and Mercury, however all three are low over the western horizon as the Sun is setting. Since this node crossing was close to the new Moon phase, about 12 hours after, there was a total solar eclipse. Visible from the Southern Hemisphere, Chile and Argentina.

   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)

Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”

   
   
   

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.


Also Follow me and other great resources at Feedspot.

Mercury at Eastern Elongation

orbital-positions    On Sunday June 23rd 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!


   I’ve added Mercury’s orbit and the orbit of Mars for an interesting comparison of an inner planet orbital path with an outer planet orbital path.

   
   
   

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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Mars – Mercury Conjunction

   Monday evening June 17th the ‘Red Planet’ Mars and the innermost planet Mercury will be at a fairly close conjunction, separated by only about 0.5o. The two planets will be about 5-6o from Pollux, one of the stars of the Gemini Twins. Both planets will nicely fit within the field of view of binoculars or a wide field eyepiece on a telescope.

   
   
   

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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