2018, September 12: Venus, Jupiter, and Moon

The sky is very clear this evening. The crescent moon, overexposed in the image, shows Earthshine. Sunlight reflected from Earth falls on the night portion of the moon and gently illuminates it.  Brilliant Venus is just above the southwest horizon.  In about 10 days, Venus begins its cycle of greatest brightness. Jupiter appears over 17 degrees to the upper left of Venus.  Jupiter gets closer to Venus during the month, but there is no conjunction.


2018: September 8: Mercury, Regulus and the Moon #astronomy #moon

September 8: Before sunrise, locate the thin waning crescent moon (28.0 d, 2%) 1.8° to the upper left of Regulus with Mercury 4.4° below the star. Mercury (m = −1.2) is only 4.5° up in the east-northeast 30 minutes before sunrise. You’ll need a clear horizon and binoculars to see the trio in bright twilight.

2018, September 6: Mercury and Regulus in the Morning Sky

September 6: In the predawn eastern sky, the waning crescent moon (26.0 d, 15%) is on a virtual line that connects the Gemini Twins, Castor (α Gem, m = 1.6) and Pollux (β Gem, m = 1.2). The moon is 9.2° from Pollux. Thirty minutes before sunrise, with binoculars, look in the east-northeast for Mercury (m = −1.1) 1.2° to the left of Regulus. Mercury is 6.5° up in the sky.

In the evening sky, Saturn’s retrograde ends. It is 5° to the upper right of Kaus Borealis (λ Sag, m = 2.8), the star at the top of the lid of the Teapot of Sagittarius, and 45° from Jupiter. Mars and Jupiter have the same visual brightness (m = −1.9). Because they have distinctly different colors, do they appear to be the same brightness to you? While they are over 70° apart, it is not appropriate in formal astronomy to compare respective objects’ brightness, but it is a fun activity. Look near the end of twilight because they have nearly the same altitude early in the evening.

2018, September 3: Moon and Aldebaran in Morning Sky

September 3: During predawn hours, the thick waning crescent moon (23.0 d, 46%) is 5.2° to the lower left of Aldebaran.

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

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, July: See Five Planets and Mars Opposition

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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.

July opens with the waning gibbous moon in the south-southwest. Mars, now the second brightest planet, is 25° up in the south-southwest, 5.8° below the moon.  At the same time, Saturn is 10° up in the southwest.  With both planets near their oppositions, they appear in the southeastern sky during the evening and move westward during the night.  During the early evening, four bright planets are arched across the sky, with the trio of bright outer planets in retrograde.

One hour after sunset, brilliant Venus stands 14° up in the west.  Venus is 9° to the lower right of Regulus.  Watch Venus close in and pass Regulus during the first 9 days of the month.  At this hour, dimmer Mercury is 4° up in the west-northwest, setting nearly 90 minutes after sunset. Use binoculars to locate it. This speedy world approaches its greatest elongation during the first half of the month.

Meanwhile, bright Jupiter, 82° to the upper left of Venus, is 33° up in the south.  This giant planet is 2° west of Zubenelgenubi.  Saturn, just past its opposition and retrograding above the Teapot of Sagittarius, is 13° up in the southeast, 52° to the lower left of Jupiter.

Mars, racing toward its opposition later in the month, rises in the southeast 117 minutes after sunset.  The Red Planet, retrograding in Capricornus, appears 34° to the lower left of Saturn.  Start looking for the five naked eye planets during the early evening.  Look for Mercury during twilight, then wait for Mars to clear the southeast horizon. Here are the highlights for the first half of the month:

  • July 1: As the sky darkens, Venus is 9° to the lower right of Regulus.  Mars rises 117 minutes after sunset this evening.  The waning gibbous moon is 15° to the left of the planet.

  • July 2: The Venus-Mercury gap is 16.6°. Mercury sets 90 minutes after sunset, its maximum setting interval after sunset for this apparition. The Venus-Regulus gap is 8° this evening.  Watch Venus close the separation during the next several evenings: 07/03, 6.9°; 07/04, 5.7°; 07/05, 4.7°; 07/06, 3.6°; 07/07, 2.6°; 07/08, 1.5°.
  • July 4: The Venus-Mercury gap is 16.2°.  Mercury’s brightness is fading fast as it approaches its greatest elongation.  This evening its apparent magnitude is 0.2, but it is appearing in bright twilight.
  • July 6: The moon is at its Last Quarter phase at 2:51 a.m. CDT. Earth is at aphelion 94.5 million miles from the sun at 11:46 a.m. CDT.

    In early July, Venus passes the next signpost of the ecliptic, Regulus. This vivid blue star is less than one degree from Venus on July 9.


  • July 9: Venus is closest to Regulus this evening, 1 degree.  The planet appears to the upper right of the star.  Watch the gap widen during the next several evenings as Venus moves away and toward Spica. Venus has a conjunction with Regulus in about 13 months when they are near their solar conjunctions, both hiding in bright sunlight.  On October 3, 2020, Venus, 22° up in the morning sky at 90 minutes before sunrise, appears 33’ below the star.  On the previous morning, Venus is 36’ above Regulus.
  • July 12: Mercury is at its greatest elongation, 26.4° east of the sun at 12:29 a.m. CDT. Mercury is only 13° above the horizon at sunset. The Venus-Mercury gap is 16.4°.  Venus is now 3.4° past Regulus.  The gap grows about 1° each evening.  The moon is at its New phase, 9:48 p.m. CDT.
  • July 14: Not long after sunset look for the waxing crescent moon 2.1° to the left of Mercury with binoculars.  Mars passes 1.1° north of Psi Capricorni.
  • July 15: Venus passes 1° to the upper right of Rho Leonis.  The waxing crescent moon is between Venus and Regulus, 1.5° to the lower right of Venus and 5.1° to the upper left of Regulus.

At mid-month, Venus continues to dominate the evening sky with its brilliance.  At 65 minutes after sunset, Venus is 11° up in the west, setting about an hour later.  Venus is now 6.5° to the upper left of Regulus.  On July 15, the waxing crescent moon is 1.5° to the lower right of Venus. Mercury, now past greatest elongation and fading quickly into the sun’s glare, sets 71 minutes after sunset.  Use binoculars to catch it in bright twilight.  Jupiter, near Zubenelgenubi, is 30° up in the south-southwest.  Saturn, 19° up in the south-southeast, is 51° to the lower left of Jupiter.  Mars, the second brightest “star” and rising 65 minutes after sunset, is approaching its perihelic opposition. It is 18° up in the southwest 2 hours before sunrise.  Here are the highlights for the second half of the month:

July 16:  The waxing crescent moon is 11.9° to the upper left of Venus.  The Venus-Regulus gap is 7.7° and growing each day.

  • July 17: Jupiter’s retrograde ends 2° west of Zubenelgenubi.  Watch Jupiter move eastward toward the star during the next month. The waxing crescent moon is 24.8° to the upper left of Venus.  If you’ve not looked for all five naked eye planets, start looking for Mercury, 30 minutes after sunset with binoculars.
  • July 18: The waxing crescent moon is 9.2° to the upper right of Spica. During the next several nights, start looking for some Perseid meteors before the moon approaches its full phase, after midnight, and before morning twilight begins.
  • July 19: The moon is at its First Quarter phase, 2:52 p.m. CDT.  This evening the moon is 13.3° to the right of Jupiter.
  • July 20: Today is the 49th anniversary of Apollo 11’s historic moon landing. This date also marks the 42nd anniversary of the Viking 1 landing on Mars.  The waxing gibbous moon is 3.5° above Jupiter this evening.
  • July 22: The waxing gibbous moon is 8.4° above Antares.
  • July 24: This evening the waxing gibbous moon is 1.9° to the upper right of Saturn.

  • July 27: Mars (m=-2.8) is at opposition.  The Full Moon is 7° to the upper left of Mars.  The moon reaches its Full phase, 3:20 p.m. CDT.  Mercury (m=1.9) 32 minutes after sunset during early twilight.
  • July 31: Earth and Mars are closest (closest approach), 35.7 million miles away.

The month ends with four bright planets lined up across the early evening sky.  Brilliant Venus is 9° up in the west 70 minutes after sunset.  Mars is 7° up in the southeast.  Mars retrogrades until August 27.  It is 30° to the lower left of Saturn, 23° up in the south-southeast, above the Teapot of Sagittarius.  It retrogrades until September 6.  This ringed wonder is 49° to the left of Jupiter.  Jupiter is 26° up in the southwest, 1.5° to the right of Zubenelgenubi.  Watch this giant world narrow the gap to the star and pass it next month.  Jupiter is 50° to the left of Venus.