I saw this really bright object fly over the house last night and at first I thought it was a plane. But it was way too bright and moved differently. A buddy of mine said it could be the ISS. How can it be that bright?
The ISS is basically just a collection of metal and solar panels, but that's exactly what makes it so bright. The sun shines on these huge surfaces, and they reflect the light straight down to you - kind of like when sunlight hits a car or a lake. That can actually be brighter than Venus or even the brightest stars, because the ISS passes relatively close to us and has a large surface area. That's why you sometimes see it during the day or at dusk as a really glaring point moving across the sky.
The reason your buddy saw it differently than a plane: the ISS doesn't have blinking lights like airplanes do, but instead moves as a constantly bright point across the sky, and the movement is also smoother. Plus it's way faster - it orbits Earth in about 90 minutes.
Are you interested in how to predict ISS passes so you can deliberately observe it? Or was it just a coincidence for you?
The thing shines so bright because the solar panels and metal surfaces act like a giant mirror - the sun hits them and the light gets reflected straight to you. Important thing: this only works when the ISS is still in sunlight while it's already dark where you are. If it's already light outside or the ISS is flying through Earth's shadow, you won't see anything even though it's passing right over your head.
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