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[Centaur]

During the evening of 2007 OCT 27 the Moon will occult the Pleiades cluster (M45). The event will be essentially over as the 95% illuminated waning gibbous Moon rises on the Chicago lakefront at 18:33 CDT. However, I’ve calculated that the graze path of Atlas, the second brightest Pleiad at magnitude 3.6, will pass through Chicagoland. Alcyone, the brightest member at mag 2.9, will emerge at 18:53:28 for lakefront viewers. All the rest of the principle stars in the group will have emerged before the Moon rises over Chicagoland.

Atlas’ southern graze path will include Plainfield, Woodridge, La Grange, Berwyn, Oak Park, Lincoln Park in Chicago and points in between. The rising star will only be 3° above the east-northeastern horizon at the time of the Chicagoland portion of the graze. Observers on the lakefront may get the best view. The graze path is only a few kilometers wide. Observers north of the path will see a full occultation. Those south of the path will see a close passage. But those on the path will have a rare opportunity to see a star winking on and off as hills and valleys of the lunar south polar region pass by.

Here are a few points I've calculated for the graze path at separations of 0.1° in longitude.

19:01:16 CDT - W 88.3° - N 41.58344°
19:01:17 CDT - W 88.2° - N 41.63676°
19:01:17 CDT - W 88.1° - N 41.69025°
19:01:18 CDT - W 88.0° - N 41.74393°
19:01:19 CDT - W 87.9° - N 41.79779°
19:01:19 CDT - W 87.8° - N 41.85183°
19:01:20 CDT - W 87.7° - N 41.90605°
19:01:21 CDT - W 87.6° - N 41.96046°
19:01:22 CDT - W 87.5° - N 42.01506°

Linear interpolation should be sufficient, but I’ll be happy to provide even more detailed data for those who reply with specific longitudes.

Below is a graphic I've created to illustrate how the graze would look from Lincoln Park on the lakefront. Atlas is on the lower right limb of the Moon.

[Chicago Astronomer - Astro Joe]

Curt,

An excellent fall lunar occultation to catch on a brisk Saturday evening.

If free, I'll see if I can set up and catch the enven visually and photographically.

Thanks for the timely info!

[Centaur]

I hope you’ll be able to observe the graze, Joe. Here’s a graphic I prepared with data for a point on the spit of land at the south side of the entrance to Belmont Harbor, where I’m predicting the graze will be seen. If you’d like data for a different location, let me know.

[Centaur]

Below are formulae I’ve developed for determining data at points along the graze path that passes through Chicagoland on 2007 OCT 27. They are only valid between western longitudes 87.6° and 88.4°. The latitude is northern. The time is CDT. The zenith angle is the position of the grazed star measured counterclockwise from the zenith along the lunar limb. The altitude is the number of degrees the star will be above the horizon at the time of the graze. The star’s coordinates are for the date of the event, not 2000.0. The input and output are all decimal. The only input is the decimal longitude. In some cases conversions will have to be made between base 60 (hours/degrees – minutes – seconds) and decimal. The graze path is about three kilometers wide.

Atlas
Magnitude +3.6
381 Light Years
RA 03:49:39.4
Dec N 24°04’48”

W = Western longitude as a positive decimal number (the only input)

M = W - 88 (M could be positive or negative, but M² is always positive)

N Latitude = 41.74382 - 0.537683 M + 0.009128 M²
Hour CDT = 19.02167 - 0.0019 M
Zenith Angle = 207.156 + 0.162 M - 0.011 M²
Altitude = 3.017 - 0.888 M + 0.013 M²

[Centaur]

Here's my map of the entire graze path for Atlas.