Posts Made By: Curt Renz

The 98% illuminated waning Moon will occult Mag +3.7 Gamma Capricorni for many North Americans during the evening of 2007 JUL 30. The southern graze path will pass through Nebraska, Iowa, Missouri, Illinois, Indiana, Ohio, Pennsylvania, New York, Massachusetts, Vermont, New Hampshire, Maine, New Brunswick, Quebec and Labrador. Observers on the graze path can witness the star winking on and off as lunar hills and valleys pass by. Those north of the path may see a full occultation. There will be no northern graze path as it would be in outer space above the North Pole. Immersion will occur on the Moon’s bright limb and emersion on the dark limb.

I’ve created a graze map for North Americans and a preview graphic with data specific to Arlington Heights, Illinois. They both can be seen by clicking: http://www.curtrenz.com/astronomical.html

Anyone desiring occultation or graze data for another location can reply to this post with a time zone, longitude, latitude and altitude above sea level. Photos and descriptions of the event would be welcome additions to this thread.

Coordinates at the time of the event (not 2000.0) for Gamma Capricorni
RA 21:40:32.4
Dec S 16°37’36”
139 Light Years

The following graze path formulae are only good between western longitudes 84° and 92°. Upon request I can provide formulae for other ranges along the graze path.

Zenith Angle is the star's position on the lunar limb measured counterclockwise from the zenith. All input and output data are decimal.

W = Western Longitude as a positive decimal number between 84 and 92 (e.g. W 89°30' = 89.5)
M = W - 88

Northern Latitude = 39.835350 + 0.049288 M + 0.012556 M²
Hour CDT = 22.00489 - 0.01197 M + 0.00057 M²
Zenith Angle = 198.868 + 0.691 M - 0.025 M²
Star’s Altitude = 10.918 - 0.781 M - 0.004 M²

Astronauts first landed on the Moon on 1969 JUL 20. That was 38 years ago today, which is exactly two Metonic periods of 19 years. Every 19 years the Moon’s monthly phases repeat on nearly the same dates. So when you gaze upon the fat crescent Moon this evening, it will appear about the same as it did when it was announced that the Eagle had landed in Tranquility Base.

Who will be the last to spot Venus after sunset during its current evening apparition? It is becoming noticeably lower in the western sky at dusk each evening. Its apparent angular size is growing as it comes closer to Earth, while it dims as its crescent narrows.

Next month Venus will pass between the Earth and Sun in inferior conjunction. Here are the hours I’ve calculated for that event by three different definitions.

IC by Right Ascension: 2007 AUG 16 at 10 hr UT
IC by Elongation: 2007 AUG 17 at 20 hr UT
IC by Longitude: 2007 AUG 18 at 4 hr UT

At inferior conjunction Venus will appear to pass 8.0° south of the Sun. That will cause it to disappear even more rapidly from the evening sky for northern hemisphere observers. But it is possible that southern hemisphere observers will be able to spot Venus as both an evening and morning star during the night of August 16/17.

Please reply to this thread with descriptions or photos of your final post-sunset observations of Venus during the current evening apparition. Be sure to note whether you observed by telescope, binoculars or naked eye. We can make it a contest to learn who will be the last Venus spotter for each category. Daytime observations are discouraged due to the danger of peering at the Sun.

I’ve created a graphic that demonstrates the position of Venus in the western sky at dusk. It can be seen on my website. Next month I will post a graphic for the coming morning apparition in the pre-dawn eastern sky. My graphics can be seen at: http://www.curtrenz.com/astronomical.html

Here’s a photo I took this evening (2007 JUL 29 at 20:33 CDT) of the Full Moon rising from Arlington Heights, Illinois. That was 8 minutes after moonrise and 18 minutes after sunset. The Moon’s shape was noticeably distorted by atmospheric refraction at its low altitude. There was a slight haze along the horizon. The lights are from a village baseball field.

A Total Lunar Eclipse will occur on Tuesday 2007 AUG 28. This will be during the pre-dawn hours for observers in North America and in the evening for those in the Far East, Australia and New Zealand. Sorry Europeans, but you’ll be shut out. Folks in eastern North America will see the Moon setting while the eclipse is in progress. That should be an intriguing site against morning twilight. Those to the west will witness the full eclipse.

I’ve created three preview panoramas of the eclipse, including data: One each for Illinois, California and Australia. The event times (when translated to Universal Time) will be the same for everyone. But the viewing perspective will vary for specific locations, so just choose the graphic for the spot closest to your own. They can be seen by clicking: http://www.curtrenz.com/astronomical.html

Photos and descriptions of the eclipse would be welcome additions to this thread.

Get ready for UFO reports. Venus soon will be popping into the pre-dawn eastern sky as the brilliant Morning Star following its inferior conjunction between the Earth and Sun on August 17th. Often this is so surprising that some astronomical illiterates, who are not used to seeing such a bright object in the sky before dawn, excitedly phone 911. 8O

I calculate Venus will achieve its greatest brilliance of the apparition at magnitude -4.6 on September 23rd. Its highest altitude before sunrise for mid-northern hemisphere observers should happen on October 26th, while its Greatest Western Elongation of 46.5° will occur on October 28th. Around that time the apparent disk of Venus will appear 50% illuminated through a telescope, like a Half Moon. It will be seen as a crescent before then and a gibbous afterward. It will eventually settle back to Superior Conjunction behind the Sun on June 8th of next year.

I’ve created a graphic demonstrating the appearance of Venus and the Moon in the eastern sky as seen from northwest suburban Chicago 30 minutes before sunrise from 2007 AUG 25 through 2008 APR 02. Although it should well serve most northern hemisphere observers. It can be seen by clicking: http://www.curtrenz.com/astronomical.html

It would be interesting to read descriptions from the first people to spot the UFO (or Venus, if you prefer) during the upcoming morning apparition.

Mercury passed behind the Sun in Superior Conjunction on August 15 and is beginning its apparition as an Evening Star. Its Greatest Eastern Elongation will be a rather large 26.0° on September 29 before dropping between Earth and Sun in Inferior Conjunction on October 23. However, the occurrence around the time of the Autumnal Equinox makes the apparition unfavorable for observers north of the tropics. The slant of the ecliptic toward the south after sunset will keep Mercury low for us northerners. But for those in the southern hemisphere, the nearly vertical ecliptic will be ideal for Mercury spotters.

Dichotomy will occur on October 4, meaning Mercury will appear 50% illuminated like a Half Moon. Before then it will be gibbous and afterward a crescent. Its stellar magnitude will be around negative one early in the apparition but will dim to positive magnitudes toward the end. A new crescent Moon will appear near Mercury on September 13 and October 13.

I’ve created two preview graphics of the apparition, one each for northern and southern hemisphere observers. To see them click: http://www.curtrenz.com/astronomical.html

Pictures and descriptions of Mercury during this apparition would be welcome additions to this thread, especially from those of you down under.

For those who get SkyNews magazine there is an article about the first quarter moon which goes on to explain that Half-Moon really isn't Half Moon but First Quarter because your only seeing 1 quarter of the lunar globe, I get that but what I don't get is:

Full Moon, why do we call it Full Moon when your only seeing Half of the lunar globe, it should be called Half-Moon imo.

Jeff

The above quote is actually from a thread on the Cloudy Nights message board. Below is my response.


American Heritage College Dictionary
half-moon, n. 1. The moon when only half its disk is illuminated.

Dictionary.com
half-moon -noun 1. the moon when, at either quadrature, half its disk is illuminated.


Of course, Jeff, you are right that the explanation you were given is nonsensical. I can see why it might have led you to believe that a Full Moon should be called a Half Moon. Whoever wrote that article is simply confounding his readers by passing along a misunderstanding about certain lunar terms. Reference to one-quarter of the lunar globe is based on a silly assumption by the writer. Those who first referred to quarters did not even know the Moon was a globe; most assumed it was a disk. The use of the term Half Moon (commonly understood as one that appears "D" shaped) is quite correct.

The terms first and last quarter do not refer to either the shape of the apparent lunar disk or a fraction of the Moon's globe. Instead, they denote the Moon's 90° quadrature (quarter of a circle in elongation) from the Sun. They are terms that were originated by astrologers who believed that the 90° separation had meaning for human affairs.

In fact, the quarters are each actually about a week in length and do not represent specific moments. The posted time for first quarter marks the end of the Moon's first quarter between conjunction (Dark or New Moon) with the Sun and eastern quadrature. The posted time for last quarter marks the beginning of the Moon's last quarter between western quadrature and conjunction with the Sun. Second quarter is the period between eastern quadrature and opposition (Full Moon) from the Sun. Third quarter is the period between opposition and western quadrature.

At the time of the quarter positions noted in publications, the apparent disk of the Moon is almost exactly 50% illuminated, thus it indeed appears as a Half Moon. Actually, the precise moment of geocentric dichotomy (Half Moon) occurs when the Earth and Sun are separated by 90° relative to the Moon's center. But that happens at an average of only 17 minutes from the posted quarter positions. From the surface of the Earth the actual times of these events can vary by as much as an hour from the geocentric times. In truth, I'm being overly precise since the Moon's terminator is not a sharp boundary.

Since the terms first and last quarter often confuse people, I tend not to use them in my publications. I recommend the terms Waxing Half Moon and Waning Half Moon or Evening Half Moon and Morning Half Moon. See my monthly astronomical calendar which presents the times of Half Moon as the moments when the disk of the Moon appears 50% illuminated from my location in Illinois. Click: http://www.curtrenz.com/astronomical.html

For those who get SkyNews magazine there is an article about the first quarter moon which goes on to explain that Half-Moon really isn't Half Moon but First Quarter because your only seeing 1 quarter of the lunar globe, I get that but what I don't get is:

Full Moon, why do we call it Full Moon when your only seeing Half of the lunar globe, it should be called Half-Moon imo.

Jeff

The above quote is actually from a thread on the Cloudy Nights message board. Below is my response.


American Heritage College Dictionary
half-moon, n. 1. The moon when only half its disk is illuminated.

Dictionary.com
half-moon -noun 1. the moon when, at either quadrature, half its disk is illuminated.


Of course, Jeff, you are right that the explanation you were given is nonsensical. I can see why it might have led you to believe that a Full Moon should be called a Half Moon. Whoever wrote that article is simply confounding his readers by passing along a misunderstanding about certain lunar terms. Reference to one-quarter of the lunar globe is based on a silly assumption by the writer. Those who first referred to quarters did not even know the Moon was a globe; most assumed it was a disk. The use of the term Half Moon (commonly understood as one that appears "D" shaped) is quite correct.

The terms first and last quarter do not refer to either the shape of the apparent lunar disk or a fraction of the Moon's globe. Instead, they denote the Moon's 90° quadrature (quarter of a circle in elongation) from the Sun. They are terms that were originated by astrologers who believed that the 90° separation had meaning for human affairs.

In fact, the quarters are each actually about a week in length and do not represent specific moments. The posted time for first quarter marks the end of the Moon's first quarter between conjunction (Dark or New Moon) with the Sun and eastern quadrature. The posted time for last quarter marks the beginning of the Moon's last quarter between western quadrature and conjunction with the Sun. Second quarter is the period between eastern quadrature and opposition (Full Moon) from the Sun. Third quarter is the period between opposition and western quadrature.

At the time of the quarter positions noted in publications, the apparent disk of the Moon is almost exactly 50% illuminated, thus it indeed appears as a Half Moon. Actually, the precise moment of geocentric dichotomy (Half Moon) occurs when the Earth and Sun are separated by 90° relative to the Moon's center. But that happens at an average of only 17 minutes from the posted quarter positions. From the surface of the Earth the actual times of these events can vary by as much as an hour from the geocentric times. In truth, I'm being overly precise since the Moon's terminator is not a sharp boundary.

Since the terms first and last quarter often confuse people, I tend not to use them in my publications. I recommend the terms Waxing Half Moon and Waning Half Moon or Evening Half Moon and Morning Half Moon. See my monthly astronomical calendar which presents the times of Half Moon as the moments when the disk of the Moon appears 50% illuminated from my location in Illinois. Click: http://www.curtrenz.com/astronomical.html

New Moon spotting is difficult for northern hemisphere observers around the Autumnal Equinox. So is Mercury spotting, despite its rather great eastern elongation when it occurs at this time of year. The celestial geometry is against us as the ecliptic at sunset slants off to the left. During the early evening of 2007 SEP 13 the Moon will be 2.5-days-old, but still hard to find. Mercury at magnitude +0.1 will be 6° to its right, and magnitude +1.0 Spica will be 5° to the Moon’s upper left. I’ve created a graphic that may help you locate the grouping. It can be seen at http://www.curtrenz.com/astronomical.html

Anyone who is successful in spotting the grouping is invited to report in this thread.