Hey All,
It's that time of year again, the beginning of
the 2006 Autumnal Equinox Geosynchronous
Satellite(geosat) Flare season. And thanks to Kevin
Fetter, I've posted a series of GIF image files of the
celestial star field where all of this will be
occurring so we all have a chance to see this. There
is also an Excel spreadsheet that has all my equations
and tables that I used to generate this. The main
image located at:
http://www.kfetter.com/jeff/geosat01.gif
I would suggest that you print this email and image
out and use it to follow the instructions below. The
80KB spreadsheet is located at:
http://www.kfetter.com/jeff/GeoSat_Flare_Table.xls
Flaring Geosats
This is when the sun, as it slides down the
ecliptic and approaches celestial equator (autumnal
equinox), illuminates the reflective surfaces and
solar array panels on all the geosats on the night
side of the earth and this light is returned to the
earth's surface on the night side. This can be quite
spectacular when viewed from below at night as "stars"
appear to form and then disappear all night long, in a
very thin line stretching east and west near the
celestial equator. Over the period of a night it looks
like someone is slowly sweeping a flashlight along a
string of diamonds. These are the brightest, "flaring"
geosats. They will rival some of the brightest stars
in the sky. And if you have a telescope or binoculars,
you can see many more geosats. They will appear as a
ghostly train of lights silently marching is a line
across the star field. At 36,000 km or nearly 5 earth
radii away, these are the most distant manmade objects
you will ever see.
Where you look depends on your latitude and the
date. Because of parallax, the geosat orbit and all of
its many satellites will appear at a specific
celestial declination depending on your latitude. For
instance at my latitude, +33N, all the flaring geosats
will appear along the -5 degree declination. Also the
best date for my latitude this year is October 7 (at 0
UT). On the diagram, which has North up and and West
to the right, there are a series of red and green dots
streching from the upper right to the lower left and
there is a red dot for me labeled "7 Oct: +32N" and
the dot lies on the -5 declination line. However, this
isn't the only date I can go outside and see flaring
geosats. If I choose other nights, I will still always
look along the -5 degree declination. The section of
the -5 degree declination I look at will be the
section directly below or above (depending on the
date) the anti-solar point –the point in the sky
exactly opposite the sun. It is not shown on my image
but it rides up the ecliptic night after night. The
ecliptic is the black line going from the lower right
of the image to the upper left. This is where the
earth's circular shadow is near. In fact, the earth's
shadow begins to cover more and more of the geosat
orbit above the anti-solar point as the autumnal
equinox is approached. The green dots to the left
(east) and right (west) of each red dot define the
chord length of the earth's shadow on the red dot's
date. This reaches a maximum on September 23 when sun
crosses the celestial equator and shadows or
"eclipses" nearly 20 degrees of the geosat orbit as
viewed from our equator. It is important to know where
the eclipse segment of the geosat orbit is because as
all geosats enter this segment from west to east they
will disappear before emerging on the east side. *And
it is usually at these entry and exit points of the
shadow that geometry is optimal for a geosat to
flare.*
Using the Graphical Calculator
To use the graphical calculator, open up the
above file in a browser or image processing
application. Then read the labels of the *red* dots
from the upper right to the lower left. Each has a
date and an earth-based latitude associated with it.
For instance, with me living at the +33N latitude, I
would use the red dot associated with the label "7
Oct: +32D" near the lower left of the image, since the
+32N latitude is closest to me. The date, "Oct 7" is
the date that flaring should be optimal for me. At the
same declination as each of the red dots in the chart
are two *green* dots of equal distance to the east and
the west. These two dots represent the eclipse entry
(the right or west green dot) and the eclipse exit
(the left or east green dot) of a geosat. *You must be
certain to only use the two green dots EXACTLY on the
same declination as the red dot.* This is hard to do
and may require a ruler to get the right set of green
dots.
So here is the procedure for using the geosat
flare graphical calculator on the optimum date for
your latitude, and then, on all other non-optimal
dates:
1.) Print out the calculator:
http://www.kfetter.com/jeff/geosat01.gif
2.) With a ruler and a pencil, draw a line - exactly
parallel with the celestial equator - across the
entire image through the red dot and the two green
dots associated with your optimal date and latitude.
(Be careful not to draw the line over any stars since
you may want to use these stars at night and don't
want them covered up in your image.) An example of
where I have done this for my optimum date (Oct 7) and
latitude (+33N) is shown here:
http://www.kfetter.com/jeff/geosat02.gif
In the image, as the night of Oct 7 progresses for me
at +33N latitude, geosats will drift from right (west)
to left (east) down the red line. As the geosats
approach the right green dot, they will brighten,
perhaps to unaided visible eye brightness (flare).
Then, as the geosats pass the right green dot, they
will disappear into the earth's shadow, only to
re-appear at the left green dot. From here they will
continue to drift east along the red line and dim
significantly.
3.) Most importantly, if I want to go out on any
"non-optimal" night, I can use the calculator on those
nights as well. Let's say, for my latitude at +33N, I
want to go out on the night of September 20. First I
would use a chart that I had already drawn my optimal
declination line (geosat02.gif, above). Then I would
draw a similar line through the September 20th red dot
and green dots. See here:
http://www.kfetter.com/jeff/geosat03.gif
4.) Then I would draw two vertical lines down from the
green dots on September 20 to my optimal declination
line for +33N. See here:
http://www.kfetter.com/jeff/geosat04.gif
Again, just like in the Oct 7 example, the geosats
will drift right to left down the red line and
disappear at the west green line and then re-appear at
the east the green line.
Other Times to Observe Geosat Flares
This calculator is designed to be used at "local
midnight", a point in time at night half way between
sunset and sunrise (not necessarily 12:00am). At this
point the red is exactly halfway between the two green
dots at it's latitude. However, as Ed Cannon and
others have seen, a great time to observe geosat
flares is at sunset and sunrise. At sunset, you would
look at the eastern horizon and see that the two green
dots are shifted such that red dot and the *right*
green dot occupy the same spot and the left green dot
has not risen above the horizon yet. Since this shows
that optimal geosat flare position (red dot) is so
close to the edge of the earth's shadow (green dot),
you will have a much better chance of seeing a geosat
flare.
IMPORTANT NOTE: This is unproven technology! I have
confidence in where the red dots go, but less
confidence in where the green dots go. I would be
interested in any observers seeing flaring occurring
*between* the green dots.
I would be interested in any feedback or
questions that anyone has on the directions or
usefulness of this graphical calculator. Please send
those questions back to me directly. And please let me
know if you have been successful as well. Enjoy this
year's Geosat Flare Season!
Regards,
Jeff Umbarger
Plano, TX USA
Lat: -96.76802W
Lon: +33.0696N
GMT-5
-------------------------------------------------------------------------
Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive:
http://www.satobs.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Tue Sep 05 2006 - 17:05:08 EDT
