Mercury at Inferior Conjunction

orbital-positions   Wednesday December 13th 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.

   While 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.

   
   
   

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.

Mercury at Eastern Elongation

orbital-positions    On Friday November 24th 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 south to southwestern horizon at sunset shining with an apparent magnitude of -0.27. About 3o above Mercury is the planet Saturn with an apparent magnitude of 0.50.

   
   
   
   
   

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.

November Moon at Apogee

   Our Moon reaches apogee, (greatest distance from Earth), on Tuesday November 21st. At that time the Moon will more or less be at a distance of 31.84 Earth diameters (406,132 km or 252,359 miles) from the Earth.

   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*

   On the day of the apogee the 3.5-day old waxing crescent Moon will be over the southwestern horizon at sunset local time. Were it not so bright the glow of the Milky Way in the background might have been visible. Saturn is visible, but it is low above the horizon.

*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.

Waxing Crescent Moon Conjunctions with Mercury and Saturn

   Over the next two evenings, November 19th and 20th the waxing crescent Moon will be passing by the innermost planet Mercury and then one of the outer planets, Saturn. The thin 1.5-day old waxing crescent Moon will be near Mercury on Sunday the 19th, and then the 2.5-day old thin waxing crescent Moon will be near Saturn on Monday the 20th.

   
   
   

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.

Mercury at Superior Conjunction

mercury at superior conjunction
   Sunday October 8th the innermost planet Mercury reaches superior conjunction – on the opposite side of the Sun from the Earth. For those that are curious, Mercury at superior conjunction is approximately 1.408 AU (130,881,776 miles; 210,633,801 km) from the Earth – the combined distance of the Earth to Sun distance plus the radius of Mercury’s orbit.
   Mercury is not visible while in conjunction with the Sun but within the next week or so Mercury will reappear on the east side of the Sun and start becoming visible over the western horizon at sunset.

   
   
   

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.

Dance of the Planets – 20 Sep. Venus / Regulus Conjunction

   This morning the inner planet Venus and the ‘heart of the lion’, the star Regulus were about 0.5o from each other. Lower near the horizon and emerging from the mornning cloud layer is the other inner planet Mercury, and just above and fainter the planet Mars.
   Camera particulars: Canon Rebel T7i; 27 mm; ISO-800; f/5.6; 8 sec.

   
   
   

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.

Dance of the Planets – Sep. 20

   The ‘dancing’ continues.
   Wednesday morning September 20th the inner planet Venus and the star Regulus will be about 0.5 o from each other in a very close conjunction. Venus is shining at an apparent magnitude of 3.9 while Regulus, the ‘heart of the lion’ has an apparent magnitude of 1.4. Both will fit within the field of view of binoculars as well as a low power or wide-field telescope eyepiece.
   Look a bit lower toward the horizon for two more planets, the innermost planet Mercury, and the ‘Red Planet’ Mars.

   
   
   

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.