Spectacular Eclipse of delta Capricorni by thin crescent Moon, Sat. evening, Jan. 20, 2007
The Eclipse of the "3rd-magnitude" star can be seen with binoculars from populous parts of the northeastern U.S.A., Ontario, and Quebec
The weather forecast is good for the populous northeast corridor and for the graze in Virginia & Delmarva; detailed maps and info. for the expedition near US 17 in Virginia are now added
Updated: 2007 January 19, 8 pm EST
Early tomorrow (Sat.) evening, shortly after sunset, the thin crescent Moon, only 4% sunlit, will eclipse the relatively bright star delta Capricorni (Deneb Algedi) for observers in populous parts of the northeastern U.S.A., Ontario, and Quebec. Sharp-eyed observers in some places might be able to see the star disappear on the Moon's dark side, but most will get a better view with binoculars. Many camcorders with optical zoom of 20x or greater might be able to accurately record the eclipse, and we encourage anyone with such a camcorder to try this. THE WEATHER FORECAST IS GOOD FOR POPULOUS AREAS Clear skies are forecast for the populous East Coast area from Boston to Washington, and down to Richmond, VA, where the interesting grazing eclipse will occur - see below. Much of Ontario will be clear, but lake effects clouds will cover most of New York, Ohio, n.w. Penn., & Michigan. There will be moderate winds in New England and Delmarva, but low humidity in most areas, and temperatures in the low 30's F. for the most populous areas. You can see the forecast maps in this Power Point file from the N. American weather forecast for astronomy of the Canadian weather service. VIEW OF THE MOON The first slide of this Power Point file shows the view of the Moon early Saturday evening along with the lines showing how the star will approach and leave the Moon for several major cities. The pm local time of the disappearance (which will be on the upper left side of the Moon) and reappearance (bottom left side of Moon) are given. For example, the disappearance for Chicago will occur at 5:04 pm CST and that for Detroit will be at 6:08 pm EST. Most of the craters shown on the Moon diagram can't be seen with binoculars, and even with telescopes, most of them will be hard to see on the dark side, which will be faintly illuminated by light reflected from the Earth (called "Earthshine"). The third slide of the Power Point file is the same as the first one, but without any of the labels. Another Power Point file shows the view for just the Washington, DC region. TWILIGHT AND HEIGHT ABOVE THE HORIZON You will need to find a place with an unobstructed view of the southwestern horizon in order to see this eclipse, called "occultation" (from the Latin for the act of hiding) by astronomers, since the Moon will be low in that direction. For example, it will be 11 degrees up (that's an eighth of the way from an ocean horizon to overhead) when the star disappears in Detroit; 6 degrees in Washington, DC; and only 2 degrees in Boston. The Moon will be higher for the disappearance in Chicago, but the twilight will be too strong for most to see it there, with the Sun only 3 degrees below the horizon; a small telescope will be needed to see the event there. In Detroit, the twilight will be bright, but with the Sun 7 degrees down, it should be possible to find the Moon with the naked eye and see the disappearance with binoculars, or some camcorders. Farther east, the sky will be darker and twilight will not be as much of a problem. TIMES AND CIRCUMSTANCES FOR DOZENS OF CITIES This Web page of the International Occultation Timing Association (IOTA) shows the worldwide region of visibility of the occultation, with the star identified by its number, 3190, in the Zodiacal star Catalog (ZC). The event will occur over a wide part of the Pacific Ocean (including Hawaii), and western and central North America, but will occur in broad daylight there, visible only with sophisticated telescopes that can be pointed in the right direction in daylight. Below the map on the IOTA Web page is a list of the times of the occultation disappearance for hundreds of North American cities, followed by a list of the time of reappearance. The reappearance will be much harder to observe since the setting Moon will be even lower in the sky (for example, 4 degrees at Detroit, 3 degrees at Washington, and only 1 degree at Philadelphia), and it will be harder to see due to interference from the light of the sunlit crescent of the Moon. Only observers with telescopes are likely going to be able to time that event. GRAZING ECLIPSE FROM BIRMINGHAM, ALABAMA TO OCEAN CITY, MARYLAND Observers in Florida and most other parts of the southeastern USA will be too far south to see the eclipse; for them, the Moon will appear to pass just north (to the right) of the star. In a three- mile-wide zone at the predicted southern edge of the eclipse "shadow", the path of the star relative to the Moon will be a tangent line. For observers in this narrow zone, the star will flash off and on a few times as is passes behind mountains and craters along the southern edge of the Moon for up to 4 minutes centered on the predicted time of closest approach. The second slide of this Power Point file shows the narrow graze path extending from just north of Birmingham, AL; then over Gadsden, AL; over Asheville, NC; and over Richmond, VA to Ocean City, MD. In Alabama, the twilight will be too strong to see this "grazing occultation", or "graze" for short, without a telescope. Although visible with binoculars, the height above the horizon will be very low in Virginia and Maryland, so observers of the graze there will need to select sites with good views to the west; the altitude will be 5 degrees in Richmond and only 3 degrees at Ocean City. A map of the path across most of Virginia and s.e. Maryland is in the second slide of this Power Point file. On it is marked the small town of Ozeana, Virginia, on US 17 about 50 miles southeast of Fredericksburg; if the sky is clear enough (the long-range forecast is favorable), you are invited to join an expedition from the Washington, DC region to help observe this event. Observers can make very detailed maps of the graze path in their area using this Google maps-based interactive Web site. GRAZING OCCULTATION EXPEDITION UPDATE So far, two expeditions are planned, one to Knotty Dam lake just north of Blairsville, Georgia, led by Harold Povenmire, cell phone 717-309-8707, and the one mentioned above to Ozeana, Virginia that I will lead. Unfortunately, overcast skies are now forecast along the graze path from Louisiana to northern Georgia, and the sky will be mostly cloudy along the path across western North Carolina, so the expedition in northern Georgia will most likely be cancelled. Clear skies are forecast for central and eastern Virginia, so I plan to undertake the expedition to the Ozeana, Virginia area near US 17. Anyone interested in this expedition should meet at 5 pm at the intersection of US 17 and route 684 (Howerton Rd.). I will be leaving home in Greenbelt, MD at about 1 pm; contact me if you'd be interested in carpooling. Those travelling separately can keep in touch by cell phone; mine is 301-526-5590. Maps showing the locations are in this Power Point file, and more detailed ones showing the three graze regions, explained below, are in this Power Point file. The predicted lunar profile is the 2nd slide of the 1st Power Point file. There are three regions of interest to try to cover near the southern limit, a northern one from 1.8 to 2.8 km northwest (measured perpendicular to the limit); a central one near the limit to a few tenths of a km northwest of it; and a southern one from 1.5 to 3.0 km southeast of the limit. TIMING THE OCCULTATION Besides timing the occultation (timings made to a few tenths of a second are useful), we also need to know the location from which you made the observation, to within about 20 feet. So unless you have a GPS receiver to measure your coordinates, don't just observe from any spot along the side of a road, but locate yourself near a house, road intersection, or other feature that you can return to later within 20 feet. Methods for timing occultations are described on this Web site of Sky and Telescope, which includes sections on "How to make occultation timings, and why" and "camcorder timing tips". Additional information about timing occultations is here. For the delta Capricorni occultation, we plan to make one recording of the Washington, DC-area FM radio station WTOP at 103.5 along with accurate WWV short-wave time signals so that others in that region can use their car or other FM radio as a time base. Others with short-wave receivers are asked to do the same with radio stations in their areas (a strong clear-channel AM station will cover a larger area) and let me know so that I can post a list of radio stations that can be used by others for timing this occultation. Good luck with your observations! David Dunham, 2007 Jan. 19, 20h UT home dunham@starpower.net 301-474-4722 cell 301-526-5590 office david.dunham@jhuapl.edu 240-228-5609