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Most subscribers learned about this service after seeing another subscriber's photograph / movie of the International Space Station transiting the disk of the sun or moon on SpaceWeather.com. Probably a slight majority don't fully understand how to interpret the reports that subsequently started appearing in their Inboxes. Hopefully, the following should help people make sense of these reports.
Jojo
was a man who thought he was a loner
but he knew it wouldn't last
Jojo left his home in Tucson, Arizona
for some California grass
Get back! Get back! Get back to where you once belonged!
Below is a report recently generated for a subscriber in Tucson, Arizona:
A - travel distance (miles) and direction B - date C - time D - elevation angle of the ISS E - azimuth angle of the ISS (positive = east from north; negative = west from north) F - range (miles) G - latitude for observing the transit H - longitude I - how far (miles) can I be from the centerline? J - is space station sunlit? K - sun elevation angle L - sun/moon separation angle LUNAR TRANSIT A------- B----- C----- D--- E----- F--- G------- H-------- I---- J K---- L---- 13.8 N 8 Dec 185815 18.9 71.7 599 32.4204 -110.9525 6.2 n -20.4 176.5 11.5 N 8 Dec 185816 18.9 71.7 598 32.3824 -110.8765 6.0 n -20.5 176.5 11.1 NE 16.54 32.3627 -110.8337 6.0 11.4 NE 8 Dec 185817 19.0 71.7 597 32.3460 -110.7975 6.1 n -20.5 176.5 13.6 NE 8 Dec 185818 19.0 71.7 596 32.3095 -110.7187 6.1 n -20.6 176.5
(Since writing this, I've added elevation data to the program, which is given in "Field I." This data is derived from the SRTM-30 data set, and represents the elevation, in meters above sea level, for the location. Also, in addition to lunar and solar transits, "planetary encounters" - when the ISS passes near a major planet - are reported as well.)
I used Microsoft Streets & Trips 2002 (it came with Microsoft Works, but is available separately) to plot these results (below). As shown above, it has a "Find" function that has a latitude & longitude mode. I simply used cut & paste to go from the report to "Find."
At the time of the transit, the angle between the center of the sun and the center of the moon (as measured from the center of the earth...) will be 176.5 degrees, which means that it'll basically be a full moon (if the angle were 180 degrees, the moon would be totally eclipsed by the earth).
The sun will be 20.5 degrees below the horizon (i.e., it will be well after sunset, which will be at 5:20:14 PM), and consequently the ISS (like the subscriber in Tucson) will be in the earth's shadow- it will therefore only be visible as a silhouette passing in front of the moon.
To observe the transit, one choice might be off of Hwy. 77 at 6:58:15 PM (a Radio Shack clock that receives the Fort Collins, CO, atomic time broadcast is nice to have for such observations).
A------- B----- C----- D--- E----- F--- G------- H-------- I---- J K---- L---- 13.8 N 8 Dec 185815 18.9 71.7 599 32.4204 -110.9525 6.2 n -20.4 176.5 11.5 N 8 Dec 185816 18.9 71.7 598 32.3824 -110.8765 6.0 n -20.5 176.5 11.1 NE 16.54 32.3627 -110.8337 6.0 11.4 NE 8 Dec 185817 19.0 71.7 597 32.3460 -110.7975 6.1 n -20.5 176.5 13.6 NE 8 Dec 185818 19.0 71.7 596 32.3095 -110.7187 6.1 n -20.6 176.5
See transit path width for another perspective on the meaning of this datum.
Rob Matson's SkyMap 6.6- using the very latest tracking information from NASA's Mission Control Center- shows the path of the ISS through the sky:
Here's a zoomed-in view:
We can obtain a similar graphical depiction using Arnold Barmettler's excellent CalSKY website (in "astronomer" mode):
| 18h58m24.33s |  ISS |
Angular Velocity: 24.1'/s. Transit duration: 1.20s Angular diameter: 19.4" size: 73.0m x 44.5m x 27.5m Satellite at az: 71.8d ENE h: 19.1d dist: 956.4 km (in shadow) Satellite apparently moves to direction 169.5° Centerline →Map: Lon:249d09m21s Lat: +32d22m38s dist: 1.85 km az: 28.7d NNE Path direction: 118.7d ESE ground speed: 8.444 km/s width: 28.1 km max. duration: 1.3 s |
Normally, CalSKY would show the path of the ISS across the moon (like here), but for some reason (as occasionally happens), that's not working right now:
Using my WorldView program in 3D graphical mode, I can show what it looks like from space as the ISS is passing across the face of the moon from Tucson, AZ: the arrow points to the ISS (marked by the gold dot); the red dot is the ISS's "lunar shadow" (this represents an updated prediction, from the prediction above; the time shown is Eastern U.S. time, however, rather than Mountain time):
Below is a zoomed-in view.
Next, the earth has been rotated (such a feeling of power :-) to line up the gold dot with the red dot, resulting in a view of the earth (and space station) as seen from the moon- in other words, "Here's looking at you, kid."
Finally, the earth has again been rotated (whew! I could use a little help, here...), showing the ISS at an altitude of about 233 miles, and its "lunar shadow" indicated on the earth's surface by the red dot (you may have to scroll to the right to see this).
Some "sky writing" out in space can also be seen- evidently done by UFO piloted by an alien computer programmer.
