2018, October 8-9: Opposing Crescents #astronomy #moon #opposingcrescents

Opposing Crescents (Credit)

 

Opposing Crescents (October 8-October 9): The morning of October 8 and the evening of October 9 present an opportunity to see very thin crescent moons, a waning crescent followed by a waxing crescent – opposing crescents. The two windows to see the two crescents are very narrow, weather dependent, and location critical.  The western wild fires and dust from the fall harvest could influence whether the crescents are visible as well.  Observing the crescents may require you to change locations.  The shortest reported interval for viewing opposing crescents is 34.6 hours by Robert C. Victor, former staff astronomer at Abrams Planetarium, Michigan State University.  This 2018 interval is about 36.3 hours.  Not a record, but certainly a test of observing skills.  Shortest intervals occur when the New moon occurs near perigee, hence moving its fastest between the two visible crescents.  Because the moon’s crescent is less than 1% illuminated, knowing the moon’s altitude and azimuth are essential.   When I asked Mr. Victor about the observing prospects, he made this analysis for my location:

The October pair is worth a try, because the timing of the New Moon for U.S. is good, and the Moon passes well north of the Sun at New. Where will you be on Oct. 8 and 9? If at your hometown, then at morning civil twilight on Oct. 8 at 06:28 CDT, the Moon will be at azimuth 91.1 deg, alt. 3.2 deg (corrected for refraction), and it will have a topocentric elongation of 9.1 degrees and be 16 hrs 19 min before New. You can preview the Moon’s location of that time by observing the Sun from the same site on Sept. 20 at 6:57 a.m.  You can start looking for the Sun earlier that morning, and where/whenever you see the Sun just above the eastern horizon relative to your horizon landscape on Sept. 20, the Moon on Oct. 8 will appear in very nearly the same place (azimuth and altitude) 29 minutes earlier. For example, if you see the Sun at 6:57 a.m. CDT on Sept. 20, then the Moon will appear in almost exactly the same place at 6:28 a.m. on Oct. 8. I used Xephem software to calculate all that.
From your location, the Moon at evening civil twilight on Tuesday, October 9, at 6:49 p.m. CDT, will be at azimuth 259.2 deg., altitude 2.5 deg., with a topocentric elongation of 11.2 degrees and an age of 20 hr 02 min. Just by an unusual coincidence, the Moon’s declination at the time it can be viewed that evening is almost precisely the same as the Sun’s. So you can preview the Moon’s location simply by noting the Sun’s location 45 minutes earlier. For example, note the Sun’s location at 6:04 p.m. (17 minutes before sunset), and the Moon will be there 45 minutes later, at 6:49 p.m.

So even for a very experienced sky watcher, some planning is necessary.

Using a planetarium program like Stellarium (stellarium.org) to calculate the crescents’ positions is helpful.  Using Google Sky during your observing may help.  Use the USNO’s online calculator  (http://aa.usno.navy.mil/data/docs/RS_OneDay.php), use Form B, to calculate the moon’s rising and setting times, and the moon’s rising and setting azimuths for your specific latitude.  On October 8, look east about 45 minutes before sunrise.  The moon is 5° up.  On the evening of the next day, about 20 minutes after sunset, look west. Mercury is 5.5° to the lower left of the very thin moon. To prepare for this, follow the moon in the morning sky as outlined in our daily notes that follow.  As the moon approaches Regulus, this should give you some indication whether you have a clear horizon for the morning observation.  On the evenings of October 7 and October 8, look for Mercury about 20 minutes after sunset.  This, again, indicates whether you have a clear horizon for the evening crescent.  For the morning observation, note the last time you see the crescent.  For the second observation record the time you first see the emerging moon.  If you view either crescent, please enter your observations here: https://tinyurl.com/opposing-crescents-2018

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2018, September 1: Mercury Approaches Regulus

 

September 1: Mercury (m = −9) is 10° up in the east-northeast, 30 minutes before sunrise.  It is approaching a conjunction with Regulus (α Leo, m = 1.3).  This morning Regulus is 7.8° below Mercury, and very difficult to locate, even with optical assistance and a perfect horizon.

In the evening sky, for most of the month, Venus (m = −4.7) and Spica (m = 1.0) set at nearly the same time, 85 minutes after sunset this evening.  As they separate, Venus moves farther south.  (Recall that the farther north an object the longer it stays in the sky.)  As they slide into twilight the largest time gap in their setting times is 15 minutes. Jupiter (m = −1.9) is 24° to the upper left of Venus. (If the Martian dust storms subside,) At 10 p.m. CDT, when Mars is near the meridian about 22° up, it may provide excellent telescopic views. Mars moved into the boundaries and in front of the sidereal backdrop of Capricornus.

2018, August 13: Venus and Moon

August 13, 2018: The crescent moon and Venus.

The waxing crescent moon is 10 degrees to the right of Venus this evening. Tomorrow evening the moon appears above Venus.

2018, August: The Evening Planet Parade Begins to Split

August opens with bright Mars in the sky nearly all night, setting about 45 minutes before sunrise.  It is just past its perihelic opposition and closest approach.  Watch Mars dim in brightness and diminish in size as our planet pulls away from its outer neighbor. Mars, the second brightest planet, shines 4° above the southeast horizon during early evening twilight. The other three bright planets – Venus, Jupiter, and Saturn – are farther west. Mercury still has an eastern (evening) elongation, but it sets only 8 minutes after the sun. This speedy planet is headed for its inferior conjunction early in the month.  At Nautical Twilight, 70 minutes after sunset, brilliant Venus, approaching its greatest elongation, is in the west between Regulus and Spica, 29° to Spica’s lower right.  Watch Venus close the gap with Spica during the month.  It is on a shorter and faster solar orbit.  Venus is slowly catching Earth in the same way Earth caught and passed Mars. (From Mars, Earth just passed what we call inferior conjunction for Earth’s inner planets.)  Jupiter is in the south-southwest in Libra, near Zubenelgenubi. Saturn, above the Teapot of Sagittarius, is in the south-southeast as the sky darkens. For the summer season the change of the length of daylight is noticeable during the month.  At the beginning of August, the sun is in the sky for 14 hours, 25 minutes.  With twilight, the dawn to dusk time is 18 hours, 13 minutes.  By month’s end daylight is reduced to 13 hours, 10 minutes and 16 hours, 38 minutes with the three phases of twilight.  Here are the highlights for the beginning of the month:

  • August 1: It’s Perseid Meteor Shower showtime!  The shower’s peak display occurs during the moon’s New phase this year.  The meteors appear to emerge from a point in space (radiant), much like the effect of falling snowflakes when you drive through a snowstorm.  During the shower period, Perseids can be seen anywhere in the sky, at any time of the night.  Some meteors are flashes that catch your eye, while others are brighter, leaving a train that persists for a short time.  Trace the path of the meteor backward toward Perseus to determine whether it’s a Perseid or a sporadic meteor (not associated with the shower). When reversing the track, the random meteor’s origin is in another part of the sky.  The highest meteor counts occur as the radiant approaches the zenith after midnight and before the beginning of morning twilight.    To get a maximum meteor count, watch in a group of five observers, four looking above each cardinal point and one looking toward the zenith.  Cut the official estimates in half if you’re observing in or near town, because many of the meteors are dim; yet, others are bright and impressive to see.  Divide the predicted rate by 5, if you’re observing alone.  It is important to note that the predicted rates for all meteors visible are across the entire sky, not visible to an individual observer.  After midnight on the peak mornings, we see the meteoroids’ orbits nearly head on. So, at prime times, lone observers may see 10 meteors per hour in a dark location, 5 per hour in town.  This evening, Venus sets at Astronomical Twilight (sun’s altitude is −18°), 150 minutes after sunset.  For the remainder of the apparition, Venus sets during twilight.
  • August 4: The moon is at its Last Quarter phase, 1:18 p.m. CDT.
The moon in the morning sky, August 6, 2018

August 6: The waning crescent moon appears near the Hyades star cluster in the eastern sky before the beginning of morning twilight. Use binoculars to explore the star clusters near the moon.

  • August 6: In the morning near the time of Astronomical Twilight, about 2 hours before sunrise, the waning crescent moon is 5.1° from Aldebaran. The star is 28° up in the eastern sky.  The moon is 1.2° above Gamma Tauri, in the Hyades star cluster. Take in the view of the moon and star cluster with binoculars. In the evening sky, Jupiter is 90° east of the sun.  One hour after sunset, it’s 23° up in the southwest, about 1° to the upper right of Zubenelgenubi.
  • August 7: Have you looked for Perseids? If you wait long enough, you’ll see a few.
  • August 8: At 2 hours before sunrise, the waning crescent moon is 13° up in the east-northeast. While not in the best observing location, use binoculars to note that the moon is 4.6° to the lower left of the star cluster M35.  Mercury is at its inferior conjunction, 9:06 p.m. CDT.
  • August 9: Start looking for Sirius about 45 minutes before sunrise for its first appearance in your morning sky before sunrise, its helical rising date.  You’ll need a clear southeast horizon as Sirius appears only about 4° above the horizon at this first appearance.  “Dog Days” may be associated with the helical rising of Sirius.  It is coincidence is this occurs during the hot, humid days of August.
  • August 10: While the moon is near its new phase, visit a remote location, even for a short visit, to see the Milky Way arching across the sky from north to south.  Look for the bright nebulae and star clusters in the southern region in Sagittarius and surrounding regions, the Sagittarius Star Cloud, and the Scutum Star Cloud.  Be sure to check out the dust clouds of the Great Rift, nearly overhead in Cygnus and follow it southward as it breaks the glow of the Milky Way into two parts.  Some of my favorite August targets are the Ring Nebula, Epsilon Lyrae, Albireo, mainly because the double stars are celestial gems to show to new observers. Albireo’s contrasting star colors always impress beginning sky watchers. With binoculars, look for the “Double Cluster” h Persei and χ Persei.
  • August 11: The moon is at its New phase at 4:58 a.m. CDT. There is a partial solar eclipse visible from north and eastern Europe, northern parts of North America, and northern and western parts of Asia.
  • August 12: Look for Perseids after midnight and before morning twilight begins.
  • August 13: This year’s peak Perseid rate may occur this morning according to NASA’s meteor expert Bill Cooke, cited in a space.com article (https://tinyurl.com/yb7ww7lh).
The waxing crescent moon appears above Venus and near the star Gamma Virginis in the early evening sky. Venus and Spica are 16° apart.

August 14: The waxing crescent moon appears above Venus and near the star Gamma Virginis in the early evening sky. Venus and Spica are 16° apart.

 

  • August 14: At mid-twilight (75 minutes after sunset, sun’s altitude is -9°), Venus is 4° up in the west. The waxing crescent moon is 6.6° to the upper left of Venus.  Gamma Virginis is about 2° to the lower right of the moon, and nearly 5° to the upper left of Venus.  Spica is 16° to the upper left of Venus.
  • August 15: At mid-twilight (60 minutes after sunset), Spica is 9° up in the west-southwest, with the waxing crescent moon (4.7 d, 27%) 6.5° above the star. The Venus-Spica gap is 15°.

 

At mid-month at evening Nautical Twilight (75 minutes after sunset), the four bright planets span the sky from east to west, ranging from Mars in the southeast, Saturn in the south, Jupiter in the southwest, and Venus low in the west.  Venus is near its greatest elongation.  Watch Venus close the gap with Spica for a widely-spaced conjunction at month’s end.  In the morning dim Mercury, only 11° west of the sun, is moving toward a favorable morning greatest elongation at month’s end.  Now, though, it is quite dim, but watch it brighten about 30 times during the next two weeks.  Continue to look for Perseid meteors.  Here’s what’s up during the second half of the month:

Jupiter passes Zubenelgenubi for the third conjunction during this appearance of the giant planet. The waxing crescent moon is nearby.

August 16: Jupiter passes Zubenelgenubi for the third conjunction during this appearance of the giant planet. The waxing crescent moon is nearby.

  • August 16: Jupiter, 18° up in the southwest at mid-twilight (50 minutes after sunset), passes 0.5° from Zubenelgenubi. This is the third conjunction during Jupiter’s apparition.  The waxing crescent moon is 7° to the right of Jupiter.
  • August 17: Venus reaches its greatest elongation (45.9°), 70 days before its inferior conjunction.  The thick waxing crescent moon  is 6.6° to the upper left of Jupiter.  Slow-moving Jupiter remains close to Zubenelgenubi, 0.6° this evening.  Watch the gap widen during the next several weeks as Jupiter creeps eastward.
  • August 18: The moon is at its First Quarter phase, 2:49 a.m. CDT.
  • August 19: At mid-twilight, Antares stands 18° up in the south-southwest with the waxing gibbous moon 10° to the upper left of the star and 16° to the right of Saturn.
  • August 20: The Venus-Spica gap is 10°. Venus is 32° to the lower right of Jupiter. This evening, the waxing gibbous moon is 3.9° to the right of Saturn.
August 20: In the early evening sky, Venus and Spica are 10° apart. Venus is 32° to the lower right of Jupiter.

August 20: In the early evening sky, Venus and Spica are 10° apart. Venus is 32° to the lower right of Jupiter.

  • August 21: This evening, the waxing gibbous moon is 8.1° to the left of Saturn, 25° up in the south during mid-twilight.
  • August 22: The moon (11.7 d, 90%) is 8.8° to the upper right of Mars.
  • August 23: At 30 minutes before sunrise, Mercury, 8° up in the east-northeast, 21° below Pollux and 22° to the lower left of Procyon. During the next two weeks, look for Mercury far below Pollux. The gap between them grows about 0.5° each day. Have you looked for Sirius during morning twilight?  In the evening sky, the moon is 8° to the upper left of Mars.
  • August 24: What is the last date that you see a Perseid meteor?
  • August 26: Mercury is at its morning greatest elongation. The separation from the sun is only 18.3°, but the ecliptic has a 25-degree inclination, favorable for locating Mercury.  Mercury rises 90 minutes before sunrise in the east-northeast. Look for it with binoculars 23° below Pollux. The moon is Full at 6:56 a.m. CDT.  In the evening sky the Venus-Spica gap is 5°.
August 27: Mars’ retrograde ends near the asterism Dog’s Country, a kite-shape group in Sagittarius. Look with binoculars when the sky gets dark.

August 27: Mars’ retrograde ends near the asterism Dog’s Country, a kite-shape group in Sagittarius. Look with binoculars when the sky gets dark.

  • August 27: Mars’retrograde ends this evening near the kite-shaped asterism Dog’s Country. The group made of Omega Sagittarii, 59 Sagittarii, 60 Sagittarii, and 62 Sagittarii.  Tonight, Mars is 2.6° from Omega Sagittarii.
August 31: A Venus-Spica Conjunction. Venus appears 1.2° below Spica.

August 31: A Venus-Spica Conjunction. Venus appears 1.2° below Spica.

 

  • August 31: Venus passes 1.2° below Spica. After this conjunction, Venus sets much earlier each evening, nearly mirroring the setting time of Spica. They disappear into bright twilight together, not setting more than about 15 minutes apart as they head toward their respective solar conjunctions.  This evening Venus is 24° to the lower left of Jupiter.

As the month ends, the summer planet parade begins to lose its brightest planet.  Now setting 85 minutes after sunset, Venus is heading toward its phase of greatest brightness.  Through a telescope, Venus displays a thick evening crescent phase that is 29.5” across.  With Venus near Spica, the pair begins to descend into evening twilight.  Speedy Mercury, now fading from the morning sky, is moving toward its superior conjunction late in September.  Jupiter, visible in the southwest in Libra east of Zubenelgenubi, appears to be heading toward an evening conjunction with Venus.  Watch what occurs next month.  Saturn, slowest moving among the other brighter planets in the planet parade, begins the evening in the south.  Spectacular Mars, shining in the sky nearly all night, starts the evening in the south-southeast.  The moon rises in the east around 10:30 p.m.  When did you first see Sirius in the pre-sunrise sky?  How many Perseids did you see? Did you check your star charts to determine the Perseids’ radiant location? Did you observe the Milky Way?

2018, July 9: Venus Passes Regulus

Brilliant Venus passes about 1 degree from Regulus this evening.  Watch as it now pulls away from this star and heads toward Spica.  That conjunction is at the end of August.

Click here for the blog’s table of contents

Look for 5 planets during the month.  From mid-northern latitudes, they are not visible simultaneously.  Look for Mercury about 30 minutes after sunset with binoculars, then wait for Mars to cross the southeastern horizon.  Four bright planets then span the sky from Mars to Venus.  Mars reaches its opposition later in the month.  The planet is closer than it’s been since 2003.

2018, July 6: Jupiter and Saturn in the Southern Sky

While Venus shines in the western sky, Jupiter and Saturn appear in the southern sky with Antares between them. The star is the brightest star in Scorpius.

Bright Jupiter, in the south-southwest, appears to the upper right of Zubenelgenubi.  Watch Jupiter approach and pass the star during the next month.

Saturn, just past its opposition, shines in the southeast, is 52 degrees to the lower ft of Jupiter.

Click here for the blog’s table of contents

Look for 5 planets during the month.  From mid-northern latitudes, they are not visible simultaneously.  Look for Mercury about 30 minutes after sunset with binoculars, then wait for Mars to cross the southeastern horizon.  Four bright planets then span the sky from Mars to Venus.  Mars reaches its opposition later in the month.  The planet is closer than it’s been since 2003.

2018, July 6: Venus Closes in on Regulus

Brilliant Venus shines from the western sky during twilight this evening. It appears about 3.5 degrees from the star Regulus that is the brightest star in Leo the Lion.

Venus passes the star on the evening of July 9.

Click here for the blog’s table of contents

Look for 5 planets during the month.  From mid-northern latitudes, they are not visible simultaneously.  Look for Mercury about 30 minutes after sunset with binoculars, then wait for Mars to cross the southeastern horizon.  Four bright planets then span the sky from Mars to Venus.  Mars reaches its opposition later in the month.  The planet is closer than it’s been since 2003.