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 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 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.)

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