Waxing Crescent Moon Near Spica

   Wednesday evening August 15th the 4.5-day old waxing crescent Moon will be about 7o from the blue-white star Spica in Virgo the Harvest Maiden.
   In addition to the Moon are five planets spread out from west to east – Dwarf Planet Ceres, and the planets Venus, Jupiter, Saturn, and Mars.

   
   
   

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Let the Moon Lead the Way


   Over the next 10 days, from August 13th to the 23rd, the Moon will move eastward, as it always does, following the ecliptic and interacting with planets and stars near the ecliptic.
   
   
   
               click on any graphic below to view each of the graphics full sized.

   
   
   

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Waxing Crescent Moon Near Venus

   Monday evening August 13th the thin 2.5-day young waxing crescent Moon will be about 10o from the inner planet Venus, and about 8o from the Dwarf Planet Ceres. However at 8th magnitude Ceres will be not be naked-eye visible, but Venus at a -4.6 apparent magnitude will be hard to miss!
   And spread out from west to east are the planets Jupiter, Saturn, and Mars.

   
   
   

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Perseids 2018 – A Good Year

   Before sunrise on Saturday August 11th, Sunday August 12th, and Monday August 13th look toward the east and southeast for ‘shooting stars’, or meteors. The short-lived streaks of light are radiating outward from the area of the constellation Perseus the Hero. These are the annual Perseids – one of the best meteor showers each year. And these three days are centered more or less on the peak.

   The Perseid Meteor Shower is named for the constellation from where the meteors radiate outward. This is the same for all meteor showers, and the ‘spot’ in the sky is known as the radiant. The Perseid radiant, as shown in the graphic, is within the Perseus constellation, and under ideal viewing conditions (dark and moonless skies) an average of about 60-80 meteors per hour could possibly be seen. This year without the interference of moonlight will increase the chances of seeing the meteors.

   The peak for this year’s Perseids is Monday September 13th at 1 UT (8 pm CDT) however Perseus and the radiant rise at around 11 pm local time. A couple of hours later should be high enough over the horizon to become visible. I always look for a triangle made from using the Pleiades open star cluster, the bright star Capella in the constellation Auriga, and a not as bright star, Mirfak in Perseus. The radiant is up to the left from Mirfak as the graphic shows.

   Best viewing times for seeing the Perseids are early morning a few hours before sunrise after Perseus has risen. This is an ideal time as the part of Earth you are viewing from is rotating toward the east, in the direction the Earth is revolving around the Sun. This means you will be seeing metaors ‘head-on’ as the enter the atmosphere.

    Meteor showers result from the Earth’s orbital path intersecting areas of comet debris. Comets, as they orbit the Sun, leave behind pieces of their icy, dirty, selves. If these debris clouds happen to be along the Earth’s orbital path then the Earth will regularly pass through the comet debris cloud. As this happens the small comet pieces hit our outer atmosphere and vaporize from the friction generated heat. We then see these as the shooting stars that make up meteor showers.

   
   
   
   

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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.

   
   
   

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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.

   
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Mars at Opposition – 2018

Mars at Opposition   Friday July 27th Mars will reach a point in its orbit around the Sun where it is at opposition relative to the Earth. at opposition The Earth is between the Sun and Mars, or any of the outer planets. At opposition both the Earth and the planet at opposition will have near identical heliocentric longitude. The opposition of Mars sometimes happens around the time that Mars is at its respective perihelion, closest to the Sun. If opposition happens during or near when the Earth is at its respective aphelion, furthest from the Sun, (first few days of July) then Mars will appear larger relative to when these dates are further apart.

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.

   
   
   

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