Moon – Jupiter Conjunction

   Tuesday morning April 23rd the 18-day old waning Gibbous Moon will be in a close conjunction with Jupiter as the two are separated by about 1o. The two should make for an interesting view as they both will very easily fit within the field of view of 7×50 binoculars.

   
   
   

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The Moon and a Dwarf Planet

   Monday morning April 22nd, before the Sun rises, look toward the south-southwest for the 17-day old waning gibbous Moon. While the Moon is obviously easy to see at a -12.60 apparent magnitude, the nearby, (2-3o), dwarf planet Ceres with an apparent magnitude of 6.90 is outshined by the Moon and is not visible.
   As this graphic shows all of the naked-eye visible planets except Mars are arranged from west to east above the horizon. While not naked eye visible Neptune, with an apparent magnitude of 7.94, is also shown. This arrangement of planets then offers an opportunity to visualize the plane of the ecliptic, the Earth’s orbit extended onto the sky. The plane of the ecliptic is one of the primary frames of reference for our solar system, and one of the things the other 7 planets have in common is that their respective orbits are all within about 7o from the plane of the ecliptic. Even our Moon stays within about 6o from the ecliptic.
   
   
   

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An Inner Planet Get Together

   Tuesday morning April 16th before the Sun rises watch for the two inner planets Mercury and Venus to be rising together and separated by about 3-4o. Both planets will easily fit within the field of view of 7×50 binoculars.
   Compare the apparent magnitude of Venus, -3.93 with the 0.22 apparent magnitude of Mercury.

   This is the closest the two will come to each other but Mercury and Venus will be visible above the horizon for the rest of the month and into May. Both planets are moving eastward along their respective orbital paths. This animated graphic is set to 1-day intervals from April 16th to April 30th.

   
   
   

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Mercury at Western Elongation

   On Thursday April 11th Mercury, the innermost planet, will reach its orbital position known as greatest western elongation at 28.0o. 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 just before sunrise local time, as this graphic shows. Venus is to the west from Mercury and further west are the giant outer planets Saturn and Jupiter. Considerably fainter and requiring optical assistance is another giant outer planet, Neptune. And completing the morning planet line-up is Dwarf Planet Ceres.

   
   
   
   
   

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Moon – Venus, Mercury, Neptune – Triple Conjunction

   Tuesday April 2nd the 27-day old thin waning crescent Moon will join three planets, Mercury, Venus, and Neptune in a triple conjunction. All four will be grouped within an area about 8-10o across. This separation is slightly more than the field of view of 7×50 binoculars.
   The group of planets and our Moon have an interesting range of apparent magnitudes. The waning crescent Moon is -9.8, Venus -3.9, Mercury 0.82, and Neptune 7.95.

   
   
   

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Planets Line Up in the Morning Skies

   Starting Monday April 1st, and continuing for a couple of weeks there will be an arrangement of 5 planets over the eastern to southern horizon in the hour or so before the Sun rises. Of these Neptune is the only one not bright enough to be visible to the unaided eye.

The Planets at 10-day Intervals During April
   The basic organization of our solar system is to have the other 7 planets follow orbits close to the plane of the ecliptic, and given how these planets are arranged and appear from the Earth this month makes it easy to visualize the ecliptic. This ‘view from above’ animated graphic shows the planets at 1-day intervals during April.

   
   
   

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Mercury at Inferior Conjunction

   Friday March 15th 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 north of the ecliptic, but angling south approaching its descending node toward the end of the 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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