Why so reflective?

Why is the ISS so reflective? It is relatively large, relatively close, with reflective panels etc...but it still seems unbelievably bright in the night sky. Any other scientific reasons why it is so glaring?

george21 – Thu, 2006 – 08 – 31 10:58


Consider the following:

1) Any object in space in space at the same distance from the sun receives the same amount of light, given the same distance from the Sun.

2) The Earth, moon and ISS are for practical purposes the same distance from the sun.

3) Although the moon looks bright at night, the light coming from the moon is about the same intensity as the light reflecting from a person on Earth (or landscape) standing outdoors on a good sunny day.

If you're a photographer, you'll recognize it as the f/16 rule --- basically, you set the camera lens opening to f/16, set the shutter speed to the ISO rating of your film, and take the photo. You'll see that the overall exposure for the person/landscape and the moon are about the same at about 18% reflectivity (although the exact amount varies as one moves across the landscape/moonscape). For highly demanding situations that might fool "dumb" cameras, photographers will measure the light reflecting off an 18% gray card and set their cameras accordingly.

So, the moon's surface has about the same overall reflectivity as Earth landscape or a general outdoor scene.

4) So (assuming) that the ISS has approximately the same reflectivity as the moon or Earth landscape, you'll get the same intensity of light.

5) If the viewing angle of the major components of the ISS (for a given overhead pass) enhances (or diminishes) the overall intensity, you get a brighter or dimmer view of the ISS.

6) Some of the solar panels and other surfaces are highly reflective, so if the angle is just right, you'll get a better reflection and a much brighter viewing.

Hope this helps to understand the situation.

Ron Hashiro, AH6RH
Honolulu, HI


Submitted by AH6RH on Sun, 2006-09-03 13:06.

Date UTC Az El Lat Lon Orbit Vis

Select your Location


Live APRS Tracking