2018: September 16-30: Venus at Greatest Brightness

September 12, 2018: Venus, Jupiter and the crescent Moon.

  • September 16: The moon reaches its First Quarter phase, 6:15 p.m. CDT.  Venus (m = −4.8) begins its period of greatest brightness, a two-week interval where it displays its greatest visual brightness.  On September 21, Venus is at its greatest illuminated extent. Many of us know this time as “greatest brilliancy.”  The two events are about a half-day apart. The instance of greatest brilliance is nearly impossible to see; rather, I note the time period when the planet displays its greatest visual brightness.  The hundredths of a magnitude that distinguish greatest brilliancy are imperceptible to our eyes.  Venus has an elongation of 40° ‒ midway between greatest elongation and inferior conjunction.  Through a telescope it has an evening crescent phase with a 25% illumination and a 40” apparent size. With these factors Venus presents to us an illuminated phase that covers more area of the sky than any other time during its apparition and it is at its brightest. (For a more technical explanation of greatest illuminated extent, see https://tinyurl.com/venus-greatest-illuminated.)
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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 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, 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.

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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.

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.

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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.

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.