# Can we detect the projected ISS shadow on the earth surface? Tags: iss, sensors - Score: 9 - Views: 2263 - Answers: 3 - Answered: yes - Asked by: Antzi (13135 rep) - Asked: 2017-08-28 - Edited: 2020-05-06 - Site: space ## Question Looking at an ISS transit picture: I started wondering wether we could see the ISS shadow passing on the earth. My intuition tells me that it would be impossible with the naked eye, but do we have any instrument able to detect it ? ## Answers ### Answer by user12102 (score: 9) TL;DR; Yes! Use a Raspberry Pi, a square millimeter photodiode, a low cost ADC and some DC and high frequency rejection with a quad op-amp and passive components. Best possible case the ISS presents about 3200 square meters of occulting area. Since the solar panels move in various ways, let's also consider half of that, or 1600 square meters. The shortest distance an observer on earth can be from the ISS is 400 km. Let's use 600 as a typical value (within 45 degrees of the zenith). Solid angle of the ISS is area/distance^2. That's between 4E-09 and 2E-08 sr. The sun's radius is about 696,000 km and distance is about 1.5E+08 km. The solid angle is pi r^2 / R^2 or about