Month: September 2018

2018, September 18: Start Looking for Vesta

  • September 18: With binoculars begin looking for Vesta (4 Vesta, m = 6.4), moving eastward among the stars of Sagittarius.  In a week it passes south of Saturn. Tonight, the minor planet is 1.3° to the lower right of 9 Sagittarii (9 Sag, m = 5.9), a star in the central area of the Lagoon Nebula (M8, NGC 6523).

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

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.