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.

Mars – Spica Conjunction


   Starting with Wednesday November 27th and continuing for the next several days the ‘Red Planet’ Mars will pass within about 3-4o from the blue-white star Spica in Virgo the Harvest Maiden. This animated graphic is set for 5:30 am CST at 1-day intervals starting with November 27th and ending on December 3rd.
   Jupiter is several degrees further east from Mars but by this time of the morning Jupiter will have just risen.

   Those familiar with the starry sky probably have heard the mnemonic “Follow the Arc to Arcturus, then speed to Spica” as a way to use the stars forming the curved handle (the ‘Arc’) of the Big Dipper as a guide to the reddish star Arcturus and then Spica. Read a bit more about following the arc from a previous post.
   
   
   

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.

2017 Summer Solstice on Mars

A Martian Year

A Martian Year – at One Earth Month Intervals

   Monday November 20th is the summer solstice on the planet Mars as the planet transitions from spring to summer during its 684 Earth day orbit around the Sun. Seasons on Mars are marked by the planet’s heliocentric longitude coordinates using the position of Mars along its orbit around the Sun. Each seasonal start/ending point is 90 degrees apart, but because of its elliptical-shaped orbit each Martian season is of varying lengths.

   I’m not exactly sure why this particular date is used but by international agreement astronomers have selected 11 April, 1955 as 0 degrees for year 1 of this Martian calendar. What this means is that on Monday November 20th, Earth time, it is the start of summer for year 34 using the aforementioned calendar system.

Year 34
0 degrees — Spring Equinox — May 05 2017
90 degrees — Summer solstice — November 20 2017
180 degrees — Fall Equinox — May 20 2018
270 degrees — Winter Solstice — October 16 2018

Year 35
0 degrees — Spring Equinox — March 23 2019
90 degrees — Summer solstice — October 08 2019
180 degrees — Fall Equinox — April 08 2020
270 degrees — Winter Solstice — September 02 2020

Year 36
0 degrees — Spring Equinox — February 07 2021
90 degrees — Summer solstice — August 25 2021
180 degrees — Fall Equinox — February 24 2022
270 degrees — Winter Solstice — July 21 2022

Learn a little (or a lot) more about the exploration of Mars at the NASA Journey to Mars web site.

   
   
   

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.

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.

Moon Conjunction with Mars and Spica


   Tuesday morning November 14th the waning crescent Moon will be within a few degrees from the ‘Red Planet’ Mars and the bluish-white star Spica in Virgo the Harvest Maiden. Then as this animated graphic illustrates the waning crescent Moon will pass by Jupiter and then Venus over the next few days.

   
   
   

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.