Mars and Saturn Line Up – Sort of

   Saturday June 9th two of the outer planets, Mars and Saturn, will be at the same heliocentric longitude of about 278o, and would be in what is called a heliocentric conjunction. Heliocentric (Sun-centered) coordinates uses an overhead view of the solar system with planet location given as degrees of heliocentric longitude. The heliocentric longitude is based on a view from the Sun and is given as the angle between a planet and the vernal equinox. The vernal equinox, 0o, is located within the constellation of Pisces the Fishes, and is the intersection between the ecliptic and the celestial equator.
   As the Earth revolves around the Sun it ‘gives’ the Sun its apparent motion eastward along the ecliptic. When the Sun crosses the celestial equator at this intersection it is moving north. At the crossing northern hemisphere winter becomes spring – the opposite seasonal change for the southern hemisphere.

   Despite having the same heliocentric longitude, when viewed from the surface of the Earth, the two show an east to west difference of about 2 hours of right ascension.

   
   
   

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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June Moon at Descending Node and Conjunction with Mars


   Sunday June 3rd the waning gibbous Moon will be crossing 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 morning of the node crossing the 19-day old waning gibbous Moon will be over the south-southeastern horizon about an hour before the Sun rises local time. The Moon will also be about 3o from the ‘red planet’ Mars. Off to the west is the planet Saturn nestled within the glow of the eastern side of the Milky Way.

   Depending on how dark the sky is where you are viewing from and how early you want to go outside, the area around Saturn is rich with some of the best deep-sky objects visible with binoculars. So the earlier you are out, before moonrise, the darker the sky will appear making it easier to see some of Messier Objects in the area near Saturn.

   
   
   
   
   

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.

June Moon At Apogee

   Our Moon reaches apogee, (greatest distance from Earth), on Saturday June 2nd. At that time the Moon will more or less be at a distance of 31.77 Earth diameters (405,300 km or 251,842 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 morning of the apogee the 18-day old waning gibbous Moon will be over the southern horizon and beteen the planets Saturn and Mars.

*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.

Moon in Conjunction with Saturn



   Thursday May 31st and Friday June 1st the just past full Moon, a waning gibbous Moon, will pass by one of the four the ringed planets, the planet Saturn. Both rise after sunset local time and will be over the western horizon before sunrise the following morning.

   
   
   
   
   
   

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.

It’s the Autumn Equinox on Mars

   Tuesday May 22nd is the autumnal equinox on the planet Mars as the planet transitions from 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. At the Martian spring equinox Mars is at 0o longitude.
   Each seasonal start/ending point is 90 degrees apart, but because of an elliptical-shaped orbit each Martian season is of varying lengths. Mars is at its greatest distance from the Sun, aphelion, before it reaches the Martian summer solstice when Mars is at 70o longitude. Perihelion, its closest to the Sun, is when Mars is at 250o longitude.
   Eccentricity of Mars and Earth for comparison.
Mars: 0.0934 – Earth: 0.0167

   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 Tuesday May 22nd, Earth time, it is the start of autumn of 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 22 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.

   Learn a little (or a lot) more about Mars at the NASA/JPL Mars Curiosity mission web site.
   Or read about the InSight mission currently on its way to Mars.

   
   
   

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.

Moon in Conjunction with Mercury and Uranus

   Sunday morning May 13th the 27-day old thin waning crescent Moon and the planets Mercury and Uranus will be in a grouping that will fit within a binocular field of view. All three rise about 1 hour before sunrise.
   This may also be an opportunity to see a crescent Moon that is within about 1 1/2 days from its new Moon phase.

   
   
   

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.

Jupiter So Close, but Yet So Far

   Thursday 10 May the outer giant ringed planet Jupiter will be at perihelion, its closest to the sun for this orbit. At perihelion, which coincidentally is 1 day after it was at opposition, Jupiter will be approximately 4.4 AU (658,230,631 km; 409,005,551 miles) from the Sun. With Jupiter this close to its opposition the planet will be rising at around sunset local time and will be visible during the night, and setting at around sunrise local time. Joining Jupiter in the morning skies are the planets Saturn and Mars, as well as the waning crescent 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.