Category Archives: Earth and Space

Postings pertaining to Earth and Space Sciences including current celestial events, exploration, and education.

Venus at Western Elongation

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inner-planets-positions   Wednesday August 12th the inner planet Venus reaches the point in its orbit called greatest western elongation. As this graphic shows the inner planet Venus, or Mercury, is more or less at a right angle (90o) from the Sun and Earth at western elongation. From the surface of the Earth, your backyard, for example, Venus is to the right, or western side of the Sun and is rising before the Sun.

   On the day of the elongation Venus will be very visible over the southeastern horizon at or before sunrise local time. Venus is joined by a few other planets, Jupiter, Uranus, Mars, and Dwarf Planet Ceres. The waning crescent Moon is nearly straight overhead (at least from 40oN) and a few degrees from the open star cluster the Pleiades. In this graphic the orbital path of Venus has been added, and also an arrow to show the direction Venus will now be moving toward (eastward).

   At western elongation Venus, or for that matter Mercury the other inner planet, is as far out from the Sun as we see them and as a result Venus or Mercury will rise at the earliest time for this orbit. Locally Venus rises that morning at around 3:00 am CDT. On the day of the western elongation Venus will be 45.8o from the Sun. From western elongation forward Venus or Mercury will be moving eastward toward the Sun and each day rising closer and closer to the time of sunrise. As the planet moves eastward it is moving further away from the Earth toward superior conjunction on the opposite side of the Sun.


    As the distance between the Earth and Venus, or Mercury, increases combined with the decreasing angle between the planet, the Earth, and the Sun, Venus or Mercury decreases in apparent size and also waxes through gibbous phase shapes but we never see it at a full phase since that is at superior conjunction.

   
   
   

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Venus Pass by M-35

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Tuesday morning August 11th the inner planet Venus will be about 3-4o from the open star cluster M-35. Located near the feet of the Gemini Twins M-35 contains thousands of stars within an area about the size of the full Moon. M-35 is located around 5,000 light years distant.

   M-35 has an apparent magnitude of approximately 5.0 so it is possible to see M-35 with the naked eye and is certainly easily seen with binoculars. For the ‘record’ Venus has an apparent magnitude of -4.31, which by comparison is ‘way brighter’!!

   
   
   

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Sun Enters Leo

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10aug-view_from-earth
   Monday 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.
   
   
   

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! – No Way!!

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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.

            Here Are Non-alternative Facts:

   This year, 2020, on Tuesday October 13th the outer planet Mars will be at opposition and 7 days (October 6th) after Mars is the closest to the Earth at 38,568,758 miles (62,070,399 km) – this time around. Coincidentally this is 3 months after Earth was at aphelion (July 4th. However this year is not the closest Mars has been from the Earth. The closest, so far, was during August 2003.

   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 using the numbers from a previous Mars opposition. 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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August Moon at Apogee

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   Our Moon reaches apogee, (furthest from Earth), for this orbit, on Sunday August 9th. At that time the last quarter Moon will be at a distance of 31.72 Earth diameters, 251,469 miles (404,700 km) from the Earth.

   On the date of the apogee the 19-day old waning gibbous Moon will be about 1o from the planet Mars and both very visible over the southern horizon in the hours before sunrise.

   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 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   
   
   
   
   
   
   
   
   

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.


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Moon – Mars Conjunction

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   Early mornings before sunrise the waning gibbous Moon is working its way eastward toward new Moon phase. Along the way the 20-day old waning gibbous Moon will be about 1o from the ‘Red Planet’ Mars on Sunday morning August 9th . Both will fit within the field of view of binoculars and should fit within the field of view of a low-power widefield type telescope eyepiece.
   The contrast in apparent magnitude is quite a range, from the Moon’s -12.0 to the -1.22 apparent magnitude of Mars.

   
   
   

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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Uranus at Western Quadrature – 2020

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   Sunday August 2nd the position of the planet Uranus, with respect to the Earth and the Sun, places this ringed planet at what is called western quadrature. At that orbital position Uranus, and actually any outer planet, is at a 90 degree angle from the Earth as this graphic shows, and also this graphic. Think third quarter Moon as that is a fair comparison of the relative positions of Earth, Sun, and Uranus.
    At western quadrature Uranus leads the Sun across the sky from east to west as the Earth is rotating, meaning that Uranus rises before the Sun and also sets before the Sun.

   
   
   This is a short video clip from a much longer video that I made as part of a live musical performance called “Orbit” at the Gottleib Planetarium in Kansas City Missouri during May 2011.

   
   
   

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A Saturday *2fer

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   Saturday August 1st there will be two opportunities for planet and Moon viewing. (a ‘2fer’)
   On Saturday morning before the Sun rises watch for the innermost planet Mercury to be about 6-7o from Pollux, one of the two ‘twin stars’ of Gemini the Twins, as this graphic is showing. Venus, if you haven’t noticed, is shining very brightly higher above the southern horizon.
   Then Saturday evening after sunset look for the 12-day old waning gibbous Moon to be about 1-2o from the outer ringed planet Jupiter and about 4-5o from another outer ringed planet, Saturn.
   
   
   
   
   *2fer – suggesting that it is possible to get two instead of one (2 for 1) of whatever is being got.
   
   
   

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July Moon at Descending Node #2

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   Friday July 31st the 11-day old 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 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.
   On the day of the node crossing the waning gibbous Moon will be a few degrees from the outer planet Jupiter and few more degrees from Saturn.

   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)

   
   
   
   
   

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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There’s a Comet in my Hair!

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   Here’s perhaps a chance to catch an interesting picture of the comet. Over the southwestern horizon Comet 2020 F3 (NEOWISE) may still be visible although its apparent magnitude (5.50) and its tail have been steadily decreasing.

   The comet is currently passing by a small y-shaped group of stars (naked-eye view) that are part of the constellation Coma Berenices over the nights of Wednesday July 29th and Thursday July 30th. Both the comet and the stars will be within the field of view of binoculars as the comet passes by the stars.

   The stars of the small constellation Coma Berenices represent the hair cut from Berenice, an Egyptian Queen, whose hair was a religious offering as a bargain for her husband to return safely from war.
   
   
   
   
   
   
   
   
    And, unmistakable over the eastern horizon is the Moon, and just rising the planets Jupiter and Saturn.

   
   
   

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