April’s Perigee Moon

22apr-perigee_moon    Our Moon orbits around the Sun with the Earth and 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*.
   The 22.86 day old waning Crescent Moon reaches perigee this month, Tuesday 23 April at 00:22 UT (7:22 pm CDT 22 April). At that time the Moon will more or less be at a distance of 29.98 Earth diameters (369,349 km or 229,503 miles) from the Earth.

   *Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

Click on graphic to see it full size.

Click on graphic to see it full size.

   Tuesday morning, 23 April, the waning crescent Moon will be close to Comet C/2012 Linear X1, however at 11th magnitude the comet is too dim for viewing and especially so close to the much, much brighter crescent Moon.
   
   
   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Sun Not In TaurusToday

The View from Earth 19 April

The View from Earth 19 April

  According to the pseudoscience of astrology the Sun enters the constellation of Taurus the Bull today, 19 April at 11 pm CDT (20 April 4 UT). When in fact the actual position of the Sun today is within the boundary of the constellation of Aries the Ram, as this graphic shows. Actually the Sun had just entered Aries 2 days ago.

   Read a little more about how astrology has the Sun incorrectly placed in a previous blog, and in another blog discussing the effects of precession.
   
   
   
   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Sun Enters Aries Today

view-from-earth-19april   Today Friday 18 April at 11 pm CDT, (Saturday 19 April 4 UT), the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation Pisces the Fishes and into the constellation of Aries the Ram. This is the true or actual position of the Sun as opposed to the pseudoscience of astrology which usually has the astrological Sun one constellation ahead or east from the Astronomical Sun’s position. Coincidentally this happens tomorrow when according to astrology the Sun enters Taurus the Bull.

   Read a little more about how astrology has the Sun incorrectly placed in a previous blog, and in another blog discussing the effects of precession.
   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Moon Near Saturn

moon-saturn-ani   Wednesday evening, 16 April, the waning gibbous Moon rises about 1 degree from Saturn, at least as viewed from my location in Missouri. For some parts of the viewing world this will be an occultation, where the Moon passes between Saturn and your view from Earth. Regardless of how close the two will be from your location the two will traverse your horizons during the night hours and be over the western horizon at your local time for sunrise. What is interesting is how the two shift positions during the hours they are above the horizon. This animated graphic is set to 0.5 second per hour.

   Click here to see a graphic showing the setting Moon and Saturn Thursday morning.

   
   
   
   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Earth Eclipses Mars Tonight!

lunar-mars-eclipse1
lunar-mars-eclipse
    Hard to believe that a major news organization can get something this incorrect! The two pictures are screen grabs from the video clip. The use of Mars starts right around the 50 second mark.
Click here to watch the video clip on the Today Show web site.

   
   
   
   
   
   
   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Mars Closest to Earth-This Time Around

   Monday 14 April not only includes the start of a Lunar Eclipse (depending on the time zone), two asteroids at or near opposition, Mars just past its opposition, Comet PanSTAARS 2012 K1 at opposition, Dwarf Planet Pluto begins retrograde motion, and at 8 am CDT (13 UT) Mars will at its closest to the Earth for this particular orbit. At that time the separation between Earth and Mars is 0.618 AU (57,446,689 miles – 92,451,484 km).
A Martian Urban Legend
   “This year, during August, Mars will be at its closest to the Earth; so close, in fact, that it will appear as large as the full Moon.”
   Have you heard this urban legend before? Since 2003, emails describing this myth have circulated the internet usually during July or August. It all started during the opposition of August 2003 when Mars was about as close as it can ever be to the Earth (55,755,723 km – 34,645,000 miles) in a 20-year cycle of varying distances at opposition. Since then, usually around August, misinformation about the appearance of Mars circulates around the internet.
What is opposition?
orbital-positions    The outer planets reach opposition when the Earth has moved into a position with the Sun on one side and the outer planet on the other side. Because all planets orbit in the same direction (toward the east), and all follow orbits that are slightly more elliptical than circular, oppositions occur at regular intervals of about 12 months (except for Mars). Mars is considerably closer to Earth and is moving faster than the other outer planets, so it takes approximately 26 months for Earth to catch up with Mars for an opposition.

Mars at the April 2014 and May 2016 Oppositions.

Mars at the April 2014 and May 2016 Oppositions.

   In the time that it takes the Earth to catch up with and move into an opposition position, the outer planets have also been moving eastward relative to the stars in the background. Over time, the constellation where the outer planet is located during opposition and its retrograde loop gradually shift to the east. An opposition is also near the time when the distance between the Earth and an outer planet is around the minimum distance. Keep in mind that because the shape of the orbit is elliptical, this minimum distance will be different each time. Since opposition for Mars is during April this year rather than in August as it was for the 2003 opposition, this should dispel the urban myth that appears every July or August since the August 2003 opposition.
   However, there is an even more conclusive way to show that Mars could never be so close that it would appear as large as the Moon. To see how use this year’s closest approach on 14 April and some basic arithmetic. You will see that Mars could not appear to be as large as our Moon unless some force somehow caused Mars to change its orbital position and literally move closer to Earth.
   On 14 April 2014, Mars will be 92,385,661 km (57,405,788 miles) from Earth. Mars is 6,792 km (4,220 mi.) in diameter. The Moon is 3,475 km (2,159 mi.) in diameter and is an average 384,400 km (238,900 mi.) from Earth. To calculate other dates, use the distance (km) values from the table below and the following formulas:

   To calculate how large Mars will appear as compared to the Moon:
   (Mars’s diameter ÷ Mars’s distance) ÷ (Moon’s diameter ÷ Moon’s distance)

   To calculate how close Mars would have to be to appear as large as the full Moon:
   (Mars’s diameter × Moon’s diameter) × Moon’s distance

Seven oppositions of Mars showing the distance when closest to Earth 
Date of opposition         Date closest to Earth       Distance (AU)  Distance (km)  
August 28, 2003            August 27, 2003                0.37272      55,758,118  
November 7, 2005           October 30, 2005               0.46406      69,422,387  
December 24, 2007          December 28, 2007              0.58935      88,165,505  
January 29, 2010           January 27, 2010               0.66398      99,329,994  
March 3, 2012              March 5, 2012                  0.67368     100,781,093  
April 8, 2014              April 14, 2014                 0.61756      92,385,661  
May 22, 2016               May 30, 2016                   0.50321      75,279,144  

   
   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Asteroids at Opposition

vesta-ceres-ani   Vesta, aka 4 Vesta, the third largest of the asteroids within the main asteroid belt between Mars and Jupiter reaches opposition Sunday 13 April. Two days later, 15 April, the closest Dwarf Planet to Earth, the former asteroid Ceres also reaches its opposition. Opposition is an arrangement with any outer planet or asteroid that is further from the Sun than the Earth. At opposition the Earth is between, in this case, either Vesta or Ceres, and the Sun. At opposition, like the full Moon, a planet or asteroid rises at sunset and is above the horizon all night and then sets at sunrise.

   Ceres, with an average diameter of 590 miles (950 km), as an asteroid was the largest and now as a dwarf planet is among the smallest if not the smallest object with enough mass to become round and thus qualify for a lateral promotion to dwarf planet status. Vesta has an average diameter of 525 km (326 miles ) and was the fourth asteroid discovered, in 1807. Vesta was also just recently visited and explored from orbit by NASA’s Dawn spacecraft. That spacecraft left orbit around Vesta in September 2012 and it is now heading for arrival at Ceres during the spring (northern hemisphere) of 2015. Vesta is also the brightest asteroid as seen from Earth and so the next few weeks offer an opportunity to perhaps see this asteroid and Ceres as they both move into and then past opposition and then moving in retrograde, westward.

Vesta and Ceres 10 April to 30 April.

Vesta and Ceres 10 April to 30 April.

   This animated graphic shows the westward motion of Vesta and Ceres as the two pass by several stars, some of which have a magnitude around Vetsa’s 5.39 and Ceres’s 6.5.

   Neither Ceres nor Vesta move fast enough to see any change in their position relative to any nearby ‘reference’ stars for at least a day or so. See if you can catch a ‘star’ changing its position relative to other stars by drawing a star chart of the stars you see in the field of view of your binoculars or telescope eyepiece. Repeat the drawing the next night, or wait another night. Do this a few times and by comparing your drawings you may find one of the dots you made for stars has shifted its position. That is the asteroid. Congratulations!

The Moon at 2 am CDT

The Moon at 2 am CDT

   Throughout this period the Moon will change from its waxing gibbous phase, pass through the Earth’s shadow for a total lunar eclipse, then begin its waning gibbous phases all the while passing past the asteroids Vesta, Ceres, Mars, Saturn, and a bunch of other celestial delights.

   
   
Caution: Objects viewed with an optical aid are further than they appear.
   Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.