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Comment by martythemaniak | Hacker News Reader

Could you explain how something that orbits 500km up could be seen at night?

Like most other satellites, it can be seen when it reflects the Sun. Satellites tend to be shiny. For an extreme case, check out "Iridium flares" - a brief but bright flares on the sky caused by old Iridium satellites, whose antennas were essentially large, rectangular mirrors.

To reflect sunlight you need the sun. If a satellite is 500km up (and 300km for later revisions), there is no way for sunlight to reach it.

There is no way to see Starlink at night. You can potentially see them for a short period around twilight.

You've really never looked into a night sky and seen a satellite? Unless you live underground or never leave a big city, it's quite easy and there are dozens of apps that will help you understand what you're looking at.

I guess the point they are trying to make is that 500km (or 300km) is essentially hugging the planet. Which means that, if it is night, they will be in the shadow for the majority of the time.

The satellites you can easily see at any time are much higher up.

> There is no way to see Starlink at night. You can potentially see them for a short period around twilight.

The time window is limited, yes. So it is not the end of the world. It is still a problem.

Here is the actual geometry at the equator, ignoring axial tilt (the blue/black circle is Earth, the red/black circle is a satellite at 500km, and the radial lines are hours): https://www.desmos.com/calculator/3br1snafmj

Starlink satellites directly overhead are in sunlight for about 1.5 hours after sunset, and the same before sunrise. Including observing on an angle, you probably lose 4 hours per night out of 12. With 300km satellites, you probably lose 3 hours. I think the situation will be worse away from the equator in summer.

Depending on the type of measureme t taken, a dark transient is also harmful. However, by far not as bad as a bright transient.

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