Posts Made By: Curt Renz

Who will be the first to spot the May New Moon with naked eyes after sunset? A combination of circumstances might make it possible for North Americans to spot the Moon aged a little more than half a day. Nevertheless, it will be a challenge and quite worthy of praise for anyone who is successful. Most folks will have better luck the next day when the Moon appears to pass near Mercury.

The Dark Moon will be in geocentric longitudinal conjunction with the Sun on 2008 MAY 05 at 12:18 UT. We’re in the months of the year surrounding the vernal equinox during which New Moon spotting is ideal for northern hemisphere observers. The current point in the Moon’s 18.6-year nodal cycle is also helpful. And being near perigee helps the Moon to separate from the Sun more quickly. For those at mid-northern latitudes the crescent on the 5th will appear in an unusual U-shape like the smiling Cheshire Cat.

I’ve created graphics previewing the western sky as viewed from Chicagoland 25 minutes after sunset for both MAY 05 and 06, although they should well serve most North Americans. They can be seen by clicking: http://www.curtrenz.com/astronomical.html

Photos or descriptions of the May New Moon would be welcome additions to this thread. Please include the date, time, time zone and location. Good Luck!

Below is a photo I took on 2007 MAY 17 of the Moon aged 30:42 hours while appearing to pass near Mercury.

The 33% illuminated waxing crescent Moon will occult Mars on 2008 MAY 10 for observers in Europe, North Africa and South Asia. For folks in India this will be an evening or twilight event. For those to the west it will occur during the afternoon but should be visible with telescopic aid (take care not to look at the Sun). Immersion will happen on the dark limb of the Moon and emersion on the bright limb.

Observers located on a graze path will be able to see lunar hills and valleys sweep across the disk of Mars. Folks between the northern and southern graze paths will see a full occultation.

I’ve created a graze map. It can be seen at http://www.curtrenz.com/astronomical.html

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

Below is a link to interviews of Americans conducted by the staff of an Australian TV program. Certainly, they edited out those who provided intelligent answers. Nevertheless, they had no trouble finding plenty of idiots in a short period of time. It causes one to wonder about the state of American education and the lack of critical thinking by adults. I find it mind boggling that each person we see being questioned in the video could cast a vote equal to my own in the upcoming presidential election.

Link: http://www.youtube.com/watch?v=C6r1IcY1pv0&feature=related

The common perception that a rising or setting Moon is magnified by the atmosphere is an optical illusion: Click link: http://en.wikipedia.org/wiki/Moon_illusion

The apparent angular diameter of the Moon actually increases slightly as it rises higher, because the rotating Earth is bringing you closer to it. When near the horizon the lower limb of the Moon is refracted higher than the upper limb, thus it appears squashed in the vertical dimension. There is no distortion in the horizontal dimension.

When you see a rising Moon, extend your arm toward it and compare the Moon to the size of a dime. If you do the same thing a few hours later, you will see that the size of the Moon has hardly changed at all.

Regarding an alleged horizontal magnification of the Moon when near the horizon, consider this thought experiment. Imagine a giant torus (hula-hoop) with its larger diameter the same as the Moon’s orbit. Picture the smaller diameter of the tube being the same as the diameter of the Moon. Then paint 720 alternately colored striped rings around the tube of the torus, each would be the same width as the diameter of the tube/Moon. To an observer at the center of the torus, the painted rings would appear to be squares.

Now imagine you are on a boat in the ocean and the torus is placed so that it is visible along your entire 360° horizon with you at its center. It would be positioned so that the bottom of the torus nearly meets the horizon with the rest of it extending upward. If the atmosphere actually magnified objects horizontally, how would that change the appearance of the rings that are supposed to look like squares from your perspective? Differing refraction levels for the top and bottom of the torus would make it appear squeezed vertically, but there is no room for the alternately colored rings (squares) to push into each others’ space. The result is that the squares would be seen as rectangles with the same width as the squares but with a lesser height.

The above thought experiment demonstrates how a rising or setting Moon may appear squashed vertically but with no distortion of its horizontal dimension.

It is true that one Full Moon can appear more than 10% larger than another one seen some months later. The difference is due to whether the Moon is near apogee or perigee. The recent Full Moon occurred near apogee making it appear smaller than usual. During the coming months the Full Moons will appear increasingly larger until the December Full Moon happening near perigee. The occasion of Full Moon at perigee (or apogee) recurs over a cycle of 14 lunar months (1.13 years). See my illustration by clicking: http://www.curtrenz.com/astronomical.html

Below is a photo I took from Arlington Heights, Illinois of the Full Moon rising on 2007 JUL 29 at 20:33 CDT. That was 18 minutes after sunset and 8 minutes after moonrise. The altitude of the center of the Moon would have been 0.9°. The Moon’s horizontal diameter was 0.5°. The apparent compression in the vertical dimension is obvious in the photo. Beneath it is a diagram I created with self-written software to show the scene as it would have theoretically appeared, taking into account the differing refraction factors for the upper and lower limbs but allowing no change in the horizontal dimension.

The common perception that a rising or setting Moon is magnified by the atmosphere is an optical illusion: Click link: http://en.wikipedia.org/wiki/Moon_illusion

The apparent angular diameter of the Moon actually increases slightly as it rises higher, because the rotating Earth is bringing you closer to it. When near the horizon the lower limb of the Moon is refracted higher than the upper limb, thus it appears squashed in the vertical dimension. There is no distortion in the horizontal dimension.

When you see a rising Moon, extend your arm toward it and compare the Moon to the size of a dime. If you do the same thing a few hours later, you will see that the size of the Moon has hardly changed at all.

Regarding an alleged horizontal magnification of the Moon when near the horizon, consider this thought experiment. Imagine a giant torus (hula-hoop) with its larger diameter the same as the Moon’s orbit. Picture the smaller diameter of the tube being the same as the diameter of the Moon. Then paint 720 alternately colored striped rings around the tube of the torus, each would be the same width as the diameter of the tube/Moon. To an observer at the center of the torus, the painted rings would appear to be squares.

Now imagine you are on a boat in the ocean and the torus is placed so that it is visible along your entire 360° horizon with you at its center. It would be positioned so that the bottom of the torus nearly meets the horizon with the rest of it extending upward. If the atmosphere actually magnified objects horizontally, how would that change the appearance of the rings that are supposed to look like squares from your perspective? Differing refraction levels for the top and bottom of the torus would make it appear squeezed vertically, but there is no room for the alternately colored rings (squares) to push into each others’ space. The result is that the squares would be seen as rectangles with the same width as the squares but with a lesser height.

The above thought experiment demonstrates how a rising or setting Moon may appear squashed vertically but with no distortion of its horizontal dimension.

It is true that one Full Moon can appear more than 10% larger than another one seen some months later. The difference is due to whether the Moon is near apogee or perigee. The recent Full Moon occurred near apogee making it appear smaller than usual. During the coming months the Full Moons will appear increasingly larger until the December Full Moon happening near perigee. The occasion of Full Moon at perigee (or apogee) recurs over a cycle of 14 lunar months (1.13 years). See my illustration by clicking: http://www.curtrenz.com/astronomical.html

Below is a photo I took from Arlington Heights, Illinois of the Full Moon rising on 2007 JUL 29 at 20:33 CDT. That was 18 minutes after sunset and 8 minutes after moonrise. The altitude of the center of the Moon would have been 0.9°. The Moon’s horizontal diameter was 0.5°. The apparent compression in the vertical dimension is obvious in the photo. Beneath it is a diagram I created with self-written software to show the scene as it would have theoretically appeared, taking into account the differing refraction factors for the upper and lower limbs but allowing no change in the horizontal dimension.

Jupiter is currently in apparent retrograde motion, and will rise late this evening here in Chicagoland at 23:23 CDT, then about four minutes earlier each succeeding night. It will be in opposition to the Sun on 2008 JUL 09. That will be true whether measured by ecliptical longitude, right ascension or greatest elongation. Near that date it will be rising around sunset, transiting the meridian around local midnight and setting around sunrise. It’s declination at opposition will be S 22.5°, meaning it still will be riding relatively low above the southern horizon for northern hemisphere observers. Its meridian transit altitude will be 67.5° minus your northern latitude.

Jupiter’s closest approach to Earth for this apparition will occur on 2008 JUL 10 at 4.1610 AU. Its apparent equatorial diameter will be 47.3 arcseconds with polar diameter at 44.2 arcseconds. Its stellar magnitude will be -2.7.

Jupiter will resume apparent direct motion on 2008 SEP 08 and reach eastern quadrature (90° from Sun) on OCT 06. Conjunction with the Sun will occur on 2009 JAN 24.

The current apparent tilt of Jupiter’s equatorial plane is -1.5° and will be virtually the same during the July opposition. That will reach 0° on 2009 APR 16. The apparent tilt oscillates with a major component equal to Jupiter’s approximately 12-year orbital period and a minor component contributed by Earth’s annual motion. It’s not an actual wobbling, but a change in our viewing perspective. The Galilean satellites all lie in planes close to Jupiter’s equatorial plane.

Mutual passages among the Galilean satellites now appear closer than they have for several years. My calculations indicate that mutual occultations, transits and shadow transits/eclipses among the Galilean satellites will commence next year on 2009 MAR 27 and end on 2010 JAN 08. Immediately prior to and during that time period I will provide detailed predictions of the events.

On my website is a graphic illustrating the apparent retrograde loop of Jupiter as it zigzags against the background stars between now and November. To see it, click: http://www.curtrenz.com/astronomical.html


Photos and descriptions of Jupiter and its satellites during the current apparition would be welcome additions to this thread.

Who will be the first to spot the June New Moon with naked eyes after sunset? The Dark Moon will be in geocentric longitudinal conjunction with the Sun on 2008 JUN 03 at 19:23 UT (14:23 CDT). The first opportunity for North Americans to sight it will occur during the evening of June 4 while aged about 30 hours.

I’ve created a graphic previewing the western sky as viewed from Chicagoland 25 minutes after sunset on June 4, although it should well serve most North Americans. It can be seen by clicking: http://www.curtrenz.com/astronomical.html

Photos or descriptions of the June New Moon would be welcome additions to this thread. Please include the date, time, time zone and location. Good Luck!

Below is a photo I took on 2007 JUL 15 of the Moon aged 38:05 hrs.

Mercury is beginning an apparition as a morning star following its inferior conjunction between Earth and Sun on 2008 JUN 07. This will not be one of the elusive planet’s ideal apparitions for northern hemisphere observers, nor will it be a bad one. Let’s just call it a challenge.

Mercury should reach its greatest western elongation of 21.8° on JUL 01 before descending to superior conjunction behind the Sun on JUL 29. As viewed from Chicagoland 30 minutes before sunrise, it will achieve its highest altitude of 8.1° on JUL 07. On JUL 06 it will appear 50% illuminated like a Half Moon. Before that date it will be a crescent and afterward gibbous.

To see my panorama for this apparition, click: http://www.curtrenz.com/astronomical.html

Photos or descriptions of Mercury would be welcome additions to this thread.

During the evening of 2008 JUN 22 the shadows of two Galilean satellites (#2 Europa & #3 Ganymede) will transit Jupiter simultaneously for many observers in North America. The same is true for those two satellites themselves. During this process a third satellite (#1 Io) will emerge from occultation.

On my website are data I’ve determined for the timing of the events and two graphics I’ve created for illustration. The first graphic displays a view from above Jupiter’s north pole and the second one is a view from Earth. To see all three of these charts go to: http://www.curtrenz.com/astronomical.html

Photos or descriptions of the events would be welcome additions to this thread.

The 81% illuminated waning gibbous Moon will occult Neptune (magnitude +7.9) for North Americans during the predawn hours of 2008 JUN 23.

I’ve created a graze map. Observers north of the graze path will see a full occultation. To see the map go to: http://www.curtrenz.com/astronomical.html

Photos or descriptions of the events would be welcome additions to this thread.