Mars Opposite Uranus

   Tuesday January 30th Mars and Uranus will reached their respective orbital positions that have them 180o apart. Mars will be located at approximately 207.6o and Uranus at approximately 27.6o of heliocentric longitude. This called heliocentric opposition.
   Interestingly at their last heliocentric opposition, February 26th 2016, Mars was located at approximately 200.0o and Uranus at approximately 20.0o of heliocentric longitude.
   
   
   

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.

A Lunar ‘4-fer’ Plus Planets: Perigee; Ascending Node; Blue Moon; and a Total Lunar Eclipse!!

   Our Moon reaches full phase for the second time this month on Wednesday January 31st at 13:27 UT (7:27 am CST). According to the popular definition for a ‘Blue Moon’ the second full Moon in a month is known as the ‘Blue Moon’. This happens about every 2.5 years with this year being a little more different in that there will be a second Blue Moon month in March.

   Our Moon reaches perigee, (closest distance from Earth), for this orbit on Wednesday January 30st at 9:48 UT (3:38 am CST). At that time the Moon will be at a distance of 28.14 Earth diameters (358,994 km or 221,204 miles) from the Earth.

      On Wednesday January 31st the full Moon will be crossing the plane of the ecliptic moving north relative to the ecliptic. This is known as the ascending node, one of two intersections the Moon’s orbital path has with the ecliptic. The ecliptic is actually the Earth’s orbit and the Moon’s orbit is inclined about 6o from the ecliptic. So there are two node intersections, the ascending and descending nodes.
      
   What do you get when you have the full Moon at a node crossing? An eclipse – in this case a total lunar eclipse. Timing for this eclipse favors viewing from the western half of the continental United States. Here is a link to download a lunar eclipse page information page (PDF) from the NASA eclipse web site
   Mid-eclipse has the darkened Moon a few degrees away from the open star cluster, M-44, commonly known as the Beehive Cluster. Both the Moon and tM-44 will fit within the field of view of binoculars.
   Here is a summary of the eclipse event starting times from the NASA Eclipse web site. My local time, CST, is UT-6 hours. An important time will be local sunrise-moonset time. For me local sunrise and Moon set time is 7:26 am CST meaning that totality will be in progress as the Moon sets. Here is a link to the Sun and Moon Data calculator web page at the U.S.N. Observatory so you may determine your local sunrise/moon set time. Here is a link to the Hermit Eclipse web site for more information about the eclipse and an interactive map showing eclipse event particulars.
P1 = 10:51 UT 4:51 CST
U1 = 11:48 UT 11:48 CST
U2 = 12:51:47 UT 6:51 CST
U3 = 14:07:51 UT 8:07 CST
U4 = 15:11:11 UT 9:11 CST
P4 = 16:08:27 UT 10:08 CST

   As the eclipsed Moon is setting in the west turn toward the south and east to see Jupiter, Mars, and Saturn plus the bright stars Spica and Antares.

   
   
   
   
   
   

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-Mars Close Conjunction

   If you were outside this morning you may have noticed over the southeastern horizon a bright star like object (Jupiter) just below a reddish star-like object (Mars). Both planets are moving eastward and Mars, as a faster orbiting planet, will gradually catch up and pass the planet Jupiter.
   Saturday and Sunday mornings January 6th-7th the planets Jupiter and Mars will be about 0.20′ (20 minutes) apart as Mars moves past Jupiter. With an apparent magnitude of -1.8 Jupiter far outshines Mars’s apparent magnitude of 1.40. This graphic is set for 7 am CST (12 UT) and the planets Mercury and Saturn are just above the eastern horizon. And further to the west higher over the southern horizon is the 20-day old waning gibbous Moon.
   This animated graphic is set to 1-day intervals starting with today, the 5th, and ending on the 7th. Both Mars and Jupiter are close enough to easily fit within the 25 mm eyepiece of a 6″ Reflector, and should make a great view with binoculars. I’m thinking that with the naked eye the two should almost merge into one, with Mars lost in the glare from Jupiter.

   
   
   

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.

Earth at Perihelion – 2018

Earth at Perihelion   Feel the Heat?
   Wednesday January 3rd at 5:35 UT (11:35 pm CST Tuesday January 2nd), as the Earth continues its annual trek around the Sun, 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, 2018, the Earth is 0.98333 AU (147,099,586 km; 91,403,445 miles) (compared with last year 2017: 0.98331 AU (147,101,082 km; 91,404,374 miles) from the Sun. Approximately one-half year or one-half revolution later, on July 6th, 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 2017. This difference in distances 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 2011 Scope on the Skies column Solar Explorations.
   Here is a good classroom activity about the Earth’s orbit and its effect on the apparent size of the Sun: Why Does the Size of the Sun Appear to Change? A Year of the Sun.

   
   
   

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.

Venus – Jupiter Close Conjunction

   Monday Morning November 13th the inner planet Venus and one of the outer planets, Jupiter, will have a very close conjunction with Venus coming within less than one-half degree from Jupiter. Adding to the celestial scenery is the planet Mars and the 25-day old waning crescent Moon.

   Both should make for a striking view with binoculars or a low-power telescope eyepiece, or as a picture. Venus will be shining at a -3.9 apparent magnitude compared with Jupiter’s -1.7 apparent magnitude.
This graphic shows a view using a 25mm eyepiece on a 6″ Dobsonian Telescope.

   
   
   

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 Continues

   In a previous post I described how the two inner planets, Mercury and Venus, and an outer planet, Mars, will be visible over the eastern horizon in the hour or so before the Sun rises. Given their respective orbital speeds the three planets will interact with one another in a series of conjunctions that at times will include the star Regulus in Leo the Lion.
   Once again facing east along 50 Highway at around 6 am CDT with early morning traffic just starting to increase. Still dealing with haze and low clouds, some of which are remnants of Hurricane Irma.

   
   
   

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.

Neptune at Opposition – 2017

   Tuesday September 5th the outer planet Neptune reaches a position in its orbit around the Sun when it is on the opposite side of the Earth from the Sun. This coincidentally is known as opposition, and it is an orbital position which only the planets further from the Sun than the Earth may reach.
   At opposition an object orbiting the Sun beyond Earth’s orbit rises and sets in a fashion similar to our Moon when it is at full phase, in that the object at opposition rises at sunset and sets at sunrise.


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.