Spectacular Occultation and Graze of Regulus

You have a chance to see 1.4-magnitude Regulus (ZC 1487) flash off and on
repeatedly among mountains and craters near the north pole on the
dark side of the 26% sunlit Moon between 0:31 and 1:26 UT June 20th
(actually early Tuesday evening, June 19th, 7:31-8:12 p.m. CDT from Kentucky to
Manitoba or 9:12-9:26 p.m. EDT from South Carolina to Tennessee). This is
the best grazing occultation in North America this year, being the
only one with a first-magnitude star on the dark side of a crescent
Moon at night.

In s.e. South Carolina, the graze might be seen without
optical aid, although steadily held binoculars are recommended for a
better view with the moderate twilight that will be present. Let me
know if you can join an expedition that I plan to lead from the
Washington, DC, area to observe the graze from parts of Charleston,
SC, or areas near there. The path passes over parts of Winnipeg, MB;
n.e. of Minneapolis; n. Illinois; s. Indiana; and over Louisville,
KY, in daylight for these places, the graze being visible with a
small telescope if the sky is clear.

The event becomes spectacular
farther southeast as the sky darkens, with the path passing near
Knoxville, Tenn.; w. of Asheville, NC; and over parts of Greenville,
Orangeburg, and Charleston, SC, as well as a short distance s.w. of
Columbia. Southwest of the mile-wide graze zone, a total
occultation can be seen, from western and southern North America, the
Caribbean Sea, and northwestern South America, as described on pages 56
and 57 of the June 2007 issue of Sky & Telescope. Predictions of the
occultation are also given for several dozen cities on a page of the main IOTA website, including a map showing the region of
visibility.

The
S&T article, and a similar version on SkyandTelescope.com,
is good for the view of the Moon showing the path of the
star for several cities. The graze will appear like the path for
Chicago, only a little farther south so that the line is tangent to
the Moon's disk with the bright star approaching the Moon from the
dark side. The graze line is path #123 on page 149 of the RASC
Observer's Handbook for 2007 (those maps, as well as tabular details
of the graze, are also on my website. The graze will last one to
three minutes.

You can zoom in on the path in great detail using the Regulus or
ZC 1487 link
on Brad Timerson's graze page.
For the interactive map, you need to enter different values for the
gray offset lines depending on the area you want to map the path.
For South Carolina, the offsets are +0.8 and -1.6 (these are
distances in kilometers from the northern limit line, plotted in green; the
most multiple events are likely in the area between the northern
offset line and the green northern limit line). These offsets don't
take into account height above sea level, which will move the zone a
little to the southwest for areas northwest of Columbia, SC; I'll
give more information about this on Monday, June 18th, on my website.

I've used the interactive
website to generate several static maps showing the path, first 3
overview maps showing it from northwest of Winnipeg to Charleston;
then four maps showing the path across South Carolina; and finally
two maps showing the path in even more detail in the Charleston, SC,
area. These maps are available in a 1-megabyte PDF file.

The profile on Brad Timerson's website is a little misleading
because it is for longitude 75°, in the ocean far southeast of
Charleston. It just uses Watts data rather than previously observed
graze data, which give a more accurate representation of what the
profile will be.

Making and Reporting Your Observations

The graze will be an interesting spectacle to watch, but even better
if you can time or videotape it; for information about timing, see
http://iota.jhuapl.edu/timng920.htm or the IOTA online observing
manual
.
Conditions are good enough in the Charleston area that the graze can
be accurately recorded just by pointing a manually focused camcorder
at the Moon.

The long-range AccuWeather forecast for South Carolina is poor, with
broken clouds expected. I haven't checked the forecast for other
areas. Hopefully the weather forecast will change. We'll be
prepared to undertake an expedition, leaving the DC area early
Monday evening, if the forecast improves, but we'll cancel the
effort if the later forecasts are also poor. I will also wait until
Sunday afternoon before making more detailed plans and selecting
specific sites. The Moon is bright enough that there's little
advantage in finding dark locations, so my plan instead is to select
a street that crosses the path with multiple places for public
access in a safe part the Charleston area where the twilight will be
darkest.

Please check the online version of this AstroAlert on Sky & Telescope's website for possible minor updates:

Any major updates will be announced via subsequent AstroAlert messages. Good luck, and clear skies!

David Dunham
Contributing Editor
Sky & Telescope
dunham@starpower.net
david.dunham@jhuapl.edu
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