21
$\begingroup$

As we can see the Starlink satellites with the naked eye as they pass by. I was wondering about what makes them visible.

Do they have large mirrors that reflect the sunlight making them look as if they have lights on board or do they actually have lights.

Improve this question
$\endgroup$

2 Answers 2

Reset to default
36
$\begingroup$

Starlink (and other satellites) categorically do not have exterior lights or illumination, that would be a waste of power for no particular benefit.

The reason that we can sometimes see satellites or other spacecraft at night is because the spacecraft is still exposed to daylight. Here is an image describing this phenomena:

Diagram of spotting satellites (image credit: Gary Meader; from the book "Night Sky With The Naked Eye" by Bob King)

Satellites and other orbiting bodies (ie the Moon) appear so bright because they're reflecting sunlight. Even though they aren't covered in mirrors, the sun is just so bright that white paint or the lunar surface is enough to let us see even tiny satellites from hundreds of kilometers away.

Occasionally, a satellite will "Flare" which is when the angle of the sun on its glass solar panels reflects directly to the observer. This reflection off the solar panels rather than simply the body of the satellite can appear much brighter temporarily.

Improve this answer
$\endgroup$
9
  • 2
    $\begingroup$ some satellites shoot lasers for LIDAR and other studies (that we can't see), and there's this but it's pretty rare but I don't know if it's one-of-a-kind, so I've asked Besides FITSat-1 (Fukuoka Institute of Technology CubeSat) have any satellites had lights meant to be visible on Earth? $\endgroup$
    – uhoh
    Commented Dec 20, 2019 at 16:29
  • 3
    $\begingroup$ @OrganicMarble possibly from here, but it should be credited in the question. $\endgroup$
    – uhoh
    Commented Dec 21, 2019 at 11:26
  • $\begingroup$ I love how the bird actually looks avian! $\endgroup$
    – dotancohen
    Commented Dec 22, 2019 at 15:00
  • $\begingroup$ The credit is mandatory, not optional. You can't just steal other people's work. Beyond that, do we even have rights to republish it here in the first place? $\endgroup$
    – Lightness Races in Orbit
    Commented Dec 23, 2019 at 12:22
  • 1
    $\begingroup$ @MitsutoshiWatanabe Yes, low orbit satellites can generally only be seen near the hours of dusk/dawn, and not late at night. This is somewhat effected by latitude, but generally you won't see any satellites about three hours after sunset. Most people worrying about observational astronomy being impacted due to starlink are not astronomers--they've been compensating for the issues caused by satellites, aircraft, and other star-obstructing phenomenon for decades. $\endgroup$
    – Dragongeek
    Commented Nov 19, 2022 at 22:51
10
$\begingroup$

I'm going to answer a slightly different question from the other answer: "why are Starlink satellites so visible, compared to other satellites?"

The answer is that they're very close to the earth; the lower edge of what might be considered a viable long-term orbit is 300 km, and some have recently been deployed at 280 km. They are boosting to a higher altitude, and once in their final orbit shouldn't be as visible.

Improve this answer
$\endgroup$
4
  • $\begingroup$ There are several different altitudes planned for the fullest implementation of Starlink, but the ones launched in 2019 are targeting only about 550 km 1, 2. They used to talk about 1100 to 1300 km but then reconsidered, because of the $1/r^2$ advantage of being closer. $\endgroup$
    – uhoh
    Commented Dec 21, 2019 at 5:06
  • 6
    $\begingroup$ The difference in visual brightness between 300 km and 550 km is only about 1.3 magnitudes ($2.5 \log_{10}((550/300)^2)$ so I don't think that "once in their final orbit shouldn't be visible to the naked eye" is true. Also remember that part of the hoopla is about their impact on ground-based astronomical observations, though messing up the night sky for all of humanity is a serious consideration as well. $\endgroup$
    – uhoh
    Commented Dec 21, 2019 at 5:07
  • 1
    $\begingroup$ I was going by the article: "where they will still be visible to binoculars and telescopes". $\endgroup$
    – user3757614
    Commented Dec 21, 2019 at 7:03
  • 1
    $\begingroup$ In a recent webcast, SpaceX stated that the difference in visual brightness once the satellites reach their operational altitude comes primarily from a subsequent change in the orientation of the satellites' solar panels, not from the additional distance created by the new, higher orbit. (Source) $\endgroup$
    – Ajedi32
    Commented Jan 21, 2020 at 15:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.