Waxing Crescent Moon – Mercury Conjunction

   Did you miss the 27-day old thin waning crescent Moon conjunction with Venus this past Monday morning? I did!
   Well there is an opportunity to see the thin crescent Moon on this side of new phase this Thursday evening January 14th. The 1.7-day young waxing crescent Moon will be over the western horizon in a line-up of sorts with Mercury, Jupiter, and Saturn all angled downward toward the western horizon. From Saturn to the Moon will span about 13o with Mercury, about 3-4o to the west, (down to the right) being the closest of the 3 planets.

   This animated graphic is set for 2-minute intervals starting at 5:30 pm CST.

   
   
   

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Morning and Evening Conjunctions

   Monday morning and evening, January 11th, offer an opportunity for catching a pair of conjunctions. Low over the eastern horizon at sunrise is the 27.7-day old very thin waning crescent Moon about 3-4o from the inner planet Venus.

   This could be a chance to see the Moon when it is about 24-hours from its new phase.

   Low in the western horizon at sunset is the ongoing triple conjunction between Mercury, Jupiter, and Saturn. Monday evening will be the closest Mercury and Jupiter will be as Mercury continues moving eastward away from the two giant planets.

   
   
   
   
   
   
   
   
   

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A Triple Conjunction – Now in Progress

   Sunday evening January 10th at sunset look toward the western horizon for the first day of a few days where there will be a series of conjunctions between Mercury, Saturn, and Jupiter. As the faster orbiting of the 3 planets Mercury will move past Saturn then Jupiter all the while the Sun, in its apparent eastward motion, will also be catching up with the two giant planets.
   The overall effect is that as Mercury moves higher above the horizon Jupiter and Saturn will be lower as each day passes. Over the next couple of weeks the Sun will move between us and Jupiter and Saturn.
   Click here to read a previous post about the triple conjunction with graphics.
   
   
   
   
   
   
   
   
                  All three planets will low over the horizon and
                  close to the Sun so be careful when observing.

   
   
   
   
   

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January Moon at Descending Node


   Sunday January 10th the nearly 27-day old waning crescent Moon crosses the plane of the ecliptic moving south. This is known as the descending node, one of two intersections the Moon’s orbital path (dark green line) has with the ecliptic.


   On the date of the descending node the 26.7-day old thin waning crescent Moon will be over the eastern horizon at sunrise local time. Just appearing above the horizon is the inner planet Venus.

   
   
   
   
   

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January Moon at Perigee

click on graphic to see it larger   Our Moon reaches perigee, (closest to Earth), for this orbit, on Saturday January 9th. At that time the Moon will be at a distance of 28.8 Earth diameters, 228,292 miles (367,400 km) from the Earth.

   On the day of the perigee Moon the 25.5-day old thin waning crescent Moon will be over the eastern horizon an hour or so before the Sun rises. And just coming into view over the eastern horizon is the inner planet Venus.

   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 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   
   
   
   
   
   

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Grand Conjunction Part 2: A Triple Conjunction!

   Just when you thought it was over, it is not! Yes Jupiter and Saturn are certainly low over the western horizon and both are setting closer to sunset, however…
   The innermost planet Mercury will be passing by Saturn then Jupiter over the next several evenings (January 7th to 12th) in a series of conjunctions as the graphics below are showing.
   Each of the conjunctions brings the three planets all within the field of view of binoculars and should make for an interesting contrast in apparent magnitudes. Jupiter: -1.94; Saturn: 0.60; Mercury: 0.89.

   
   
            Be careful observing because the Sun is close.

   
   
   

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Last Quarter Moon – Spica Conjunction

   Wednesday morning, January 6th in the hour or so before sunrise look for the last quarter Moon to be about 6o from the blue-white star Spica in Virgo the Harvest Maiden. Since the Moon is in constant motion by the same time Thursday morning the Moon, now a waning crescent, will have moved from the west side of Spica to be about 9-10o east from Spica.

   
   
   

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Moon – Regulus Conjunction


   Late Saturday evening January 2nd, or early Sunday morning the 3rd, watch for the 20-day old waning gibbous Moon to be about 6-7o from the star Regulus. Regulus is the ‘heart’ of the lion, the constellation Leo the Lion.

   
   
   

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Earth at Perihelion – 2021

   Feel the Heat?
   As the Earth continues its annual trek around the Sun, Saturday January 2nd at 13 UT (7 am CST), the Earth reaches a point in its orbit that is called perihelion. Perihelion is the minimum distance that separates the Earth from the Sun, and we are the closest to the Sun for the year at this point in the orbit. So this year, 2021, the Earth is 0.9833 AU; 91,403,445 miles; 147,099,586 km from the Sun.

   Approximately one-half year or one-half revolution later, on July 5th, the Earth is at aphelion and is 1.0167 AU (94,508,169 miles; 152,096,155 km), its maximum distance from the Sun for 2020. This approximately 3% difference in distances between perihelion and aphelion is due to the shape of the Earth’s orbit being elliptical rather than circular. However the Earth has a mildly elliptically shaped orbit that is closer to being slightly out-of-round than the incorrect, very elliptical orbit that is often shown – like the illustration used here.

sun2014-ani   In Astronomy the shape of a planet’s orbit is called eccentricity, with 0 being a circle and 1 a straight line. Any value between 0 and 1 represents an ellipse. The shape of the Earth’s orbit is so close to being circular that the apparent size of the Sun does not appear to change as this animated graphic shows. The difference between perihelion and aphelion is about 3%.

   Eccentricity for each planet is listed below for comparison.

Planet	   Eccentricity	
Mercury	   0.2056
Venus	   0.0068
Earth	   0.0167
Mars	   0.0934
Jupiter	   0.0484
Saturn	   0.0542
Uranus	   0.0472
Neptune	   0.0086
Pluto	   0.2488

   To read more about the Earth’s orbit and get some teaching ideas click here to download a PDF copy of my January Scope on the Skies column Solar Explorations.


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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New Year’s Eve 2020

   The evening skies of this year’s New Year’s Eve begins at sunset with two of the giant planets, Jupiter and Saturn, low over the western horizon at sunset, but still within about 1o from each other. Higher over the southern horizon is the planet Mars. And with optical assistance or a camera the other two gas giant planets, Uranus and Neptune, as well as Dwarf Planet Ceres could be seen.

   Later, at around midnight and centered over the southern horizon will be the ‘regular’ Northern Hemisphere winter display of stars. This is a familiar groups of bright stars in a rough circle around the constellation of Orion the Hunter, and sometimes referred to as the “Winter Hexagon” or ‘Winter Circle”.

   As the winter hexagon the member stars are Rigel in Orion the Hunter, Aldebaran in Taurus the Bull, Capella in Auriga the Charioteer, Pollux and Castor in the Gemini Twins, Procyon in Canis Minor, and Sirius in Canis Major.


   
   
   
   We’ve survived another orbit.
   
   
          Happy New Year!
   
   
   
   
   
   
   
   
   

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