Sun Enters Leo

10aug-view_from-earth
   Friday August 10th the Sun in its apparent eastward motion along the ecliptic, moves out of the constellation Cancer the Crab and into the constellation of Leo the Lion. 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.

   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.
   
   
   

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August Perigee Moon at Ascending Node, and a Partial Solar Eclipse

   Friday August 10th the 28.5 day old waning crescent 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.

   Does our Moon actually go around the Earth as many graphics show? 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 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?”

Perigee Moon
   Our Moon reaches perigee, (closest distance to Earth), for this orbit on Friday August 10th. At that time the Moon will be at a distance of 28.07 Earth diameters (358,100 km or 222,513 miles) from the Earth. The Moon will also be 28.5 days old, and only 15.8 hours from new Moon Phase.
    When the time of perigee is close to a node crossing there will be either a lunar or solar eclipse. In this case less then 24 hours after the node crossing there will be a partial solar eclipse. This solar eclipse is only visible from Arctic, Greenland and parts of Asia.

   
   
   

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Mercury at Inferior Conjunction

orbital-positions   Wednesday August 8th 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.

   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 7o south, its maximum latitude south from 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.


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Jupiter at Eastern Quadrature

   On Monday August 6th the position of the planet Jupiter with respect to the Earth and the Sun places the solar system’s largest planet at an orbital position called eastern quadrature. Jupiter is at a 90 degree angle from the Earth as this graphic shows. Think first quarter Moon as that is a fair comparison of the relative positions. At this position Jupiter follows the Sun across the sky from east to west as the Earth is rotating, meaning that Jupiter rises after the Sun and consequently sets after the Sun.

   Where is Jupiter now? This graphic shows the sky at 10 pm CDT to include Jupiter high above the southwestern horizon.

   This is a short 6-7 minute video I made as part of a live musical performance called “Orbit” that was performed at the Gottleib Planetarium in Kansas City Missouri in May 2011. This is a piece from the much longer tour of the solar system performance and video and shows Jupiter, Saturn and some of their moons as viewed from the Cassini spacecraft.

   
   
   

Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.

Taurus Noses the Moon

   Monday morning August 6th the 24-day old waning crescent Moon will be about 4o from the reddish star Aldebaran, part of the open star cluster the Hyades. This v-shaped cluster of stars marks the face of Taurus the Bull, and Aldebaran represents the red ‘angry’ eye of Taurus.

   
   
   

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A Sky Full of Planets

   Friday August 3rd all of the planets, except for Mercury, and some of the Dwarf Planets will be over the horizon during the hours before sunrise and the hours before sunset. The dwarf planets Pluto (14.2), Haumea (17.2), Makemake (16.7), and Eris(18.5) with low apparent magnitudes are too distant to be visible other than with larger aperture telescopes. However Dwarf Planet Ceres, at 8th magnitude could be visible with smaller telescopes and certainly with long exposure time imaging.

   
   
   

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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Mars as Big as the Full Moon – But Only on Internet

   Tuesday July 31st the outer planet Mars will be at its closest to the Earth – this time around. Coincidentally this is 4 days after Mars was at opposition, and about 3 weeks after Earth was at aphelion. However this is not the closest Mars has been from the Earth. The closest, so far, was during August 2003.

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.

   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.

   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 requires 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 July 31st, Mars will be 57,595,180 km (35,787,986 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. In terms of apparent size our Moon has an angular diameter of 0.5o (30 arc minutes or 1800 arc seconds), while on July 31st Mars has an apparent diameter of 24 arc seconds.
    So with the following calculation using those values (24 / 1800) x 100% = 1.3%) Mars is only 1.3% the apparent size of our Moon.

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

         (4220 / 35787986) / (2159 / 238900) = 0.013 = 1.3%
    In other words, Mars on 31 July will be only 1.3% of the apparent size of the 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.

   
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