Table of Contents

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).
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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.)

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, September 4: North American Nebula, Have You Seen It? #astronomy

The North America Nebula 
Credit & Copyright: Jason Ware

September 4: As the moon approaches its new phase, look for the Milky Way arching across the evening sky. Cygnus, with its bright star Deneb (α Cyg, m = 1.2), appears to be flying southward along the soft glow of our galaxy. It ranks near the bottom of the 20 (visually) brightest stars list. Along with Rigel (β Ori, m = 0.2), Deneb is one of the brightest stars in our sky. Both stars are approximately 100,000 times brighter than our sun. Deneb seems dimmer to us because it is likely twice the distance of Rigel, and it is surrounded by fewer bright stars. It seems less notable than those stars that gleam from the Orion region of the sky. The Cygnus neighborhood is crowded with dim features. Walter Scott Houston, the expert chronicler of deep sky observing, noted this in his columns in Sky & Telescope magazine. Houston explained that certain sections of the sky had many objects that were not identified on charts, especially those in the densely packed Milky Way. His articles were compiled into a book, Deep-Sky Wonders, by Stephen James O’Meara. In the chapter for September, Houston provided accounts of viewing the North American Nebula. Houston’s description: “One of the most controversial objects among amateur astronomers, the North American Nebula, is familiar from photographs as a large diffuse glow about 3° east and 1° south of Deneb. There has been remarkable diversity of opinion on how small a telescope can show this object visually” (p. 202). While I have never seen it naked eye, Houston stated that some observers reported seeing it without optical assistance. (If you’ve seen the nebula without a telescope or binoculars, describe your observations for me. Enter your description on this document: https://tinyurl.com/north-american-nebula.)