# RE: reflectance 101 (or duh?)

R_John@Rmatsc.Riem.Com
Mon, 13 Apr 1998 10:58:09 -0700

```Jeff,
The basic problem is the way you drew your diagram.  You show
the sun being 30 degrees above the 'observer's horizon.  While this is
certainly true, what is important is where the sun's rays are coming
from with respect to the Iridium.  For this, draw a line FROM THE
IRIDIUM to the sun.  This line will be parallel to the line between the
observer and the sun.  Now the angle between the sun-Iridium line
and the Iridium-Jeff line is 150 degrees.  This means the angle between
the MMA and sun (or MMA and Jeff) is 15 degrees.  Add 15 to the 30
that the sun is above the local horizon and you see that the MMA is
at a 45 degree angle to the local horizon.  Since the Iridium was about
4 degrees (in longitude) West of you, I get 46 degrees which is
pretty close the 45 we were looking for.
Randy

Pick a non-proportional font:

Z    M       S
|   /      /
|  /    /
| /  /
|//
Z      I------------H
|     /|
|    / |
|   /  |
|  /   |
| /    |
|/     |
J      N

J = JEFF
Z = ZENITH
I = IRIDIUM
M = MMA PLANE
S = SUN
H = HORIZON (JEFF'S)

HIS = 30
JIS = 150 DEGREES
ZJI = JIN = 30
MIZ = 40
MIS = 15 (also mIJ, not shown)
Now rotate ZI (and therefore IM) 4 degrees clockwise
and the MMA is 46 degrees above the horizon.

> -----Original Message-----
> From:	jeff@satellite.eu.org [SMTP:jeff@satellite.eu.org]
> Sent:	Saturday, April 11, 1998 6:25 AM
> To:	SeeSat-L%cds.plasma.mpe-garching.mpg.de@Mail.Riem.Com
> Subject:	reflectance 101 (or duh?)
>
> Hi,
>
> I'm predicted to see (maybe) a mag -7 flare from Iridium 42 late this
> afternoon (April 11) at ~16:53 local (20:53 UT).  The sat will be at my
> el 61 deg. and azimuth 261 deg. This puts the sat to the west of my
> location and the sun is ~30 deg. above my horizon at an azimuth of ~255
> deg (to my west).
>
> How do I get a reflection of the sun with the sat west of me? Isn't the
> angle between the sunlight hitting the MMA and the reflection back down
> to me at 90 degrees from this nearly flat MMA? It would seem it isn't:-(
>
> The MMA is angled down from the body of the sat 40 deg. or 50 deg. above
> the earth's surface if it was directly overhead. The sat, in fact, will
> be to the west of me, effectively making the top of the sat (in
> relationship to myself, tilt to the west (I think). If the sun is above
> the local horizon, how is that reflected light directed toward me when
> the sat is to the west of me?
>
> Sure wish I could draw a better picture here. What am I overlooking?
>
> Respectifully,
>
> Jeff Hunt <jeff@satellite.eu.org>
> 38.51N/76.76W
>                              sat body
>                                 |                              sun
> E                               |                               *   W
>                               \ | /MMA
>                                \|/
>
>
>
>
>
>
>                            ?
>                       me wondering
```