Why are SL's blue when in a train? [Because the solar panels are blue]

[Maury Markowitz]

Just realized I've seen this multiple times and never thought about it...

Why are SL satellites blue when they are still in the train?

And why are they even visible given they are often seen far from the flare zone in these cases?

I've only seen a train once, last summer, and it was directly overhead (actually a bit to the east) where they are normally completely invisible.

 

[Mendel]

And why are they even visible given they are often seen far from the flare zone in these cases?

Where the flare zone is depends on how the surfaces on the satellite are oriented, and that changes.

Article:

There will be a small percentage of instances when the satellites cannot roll all the way to true knife edge to the Sun due to one of the aforementioned constraints. This could result in the occasional set of Starlink satellites in the orbit raise of flight that are temporarily visible for one part of an orbit.

This simple diagram highlights why satellites in orbit raise are so much brighter than the satellites that are on-station.

Source: https://spaceref.com/science-and-exploration/spacex-publishes-update-on-starlink-satellite-brightness-issue/

 

[flarkey]

Theres a difference between the two types of sighting. Starlink trains are illuminated by diffuse light from the sun and they're much closer to the observer (maybe 400km). The flares are a specular reflection, essentially a glint of sunlight and are about 2000km away.

As to why they look blue, I'm not sure. Do they look blue, or do cameras image them as blue? Maybe they're blue for the same reason the sky is blue - Reyleigh scattering.

https://spaceplace.nasa.gov/blue-sky/en/#:~:text=The Short Answer:,sky most of the time.

Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered more than the other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time

 

[JMartJr]

Maybe they're blue for the same reason the sky is blue - Reyleigh scattering.

Wouldn't that have the opposite effect, scattering the blue light and leaving the rest of the spectrum coming straight at you from the satellite... in effect making them look a bit less blue?

 

[Mendel]

As to why they look blue, I'm not sure. Do they look blue, or do cameras image them as blue? Maybe they're blue for the same reason the sky is blue - Reyleigh scattering.

Midday sunlight is bluer than morning or evening sunlight. Likewise, a Starlink train overhead appears bluer than a Starlink train near the horizon.
This especially true if the camera's white balance has been set to warm indoor lighting.

diffuse light from the sun

You mean, we see a diffuse reflection?
In that case, the satellite could appear blue because it is? (e.g. blue solar panels) but I don't really know

 

[Mendel]

Wouldn't that have the opposite effect, scattering the blue light and leaving the rest of the spectrum coming straight at you from the satellite... in effect making them look a bit less blue?

compared to what?

 

[JMartJr]

compared to what?

Compared to what the light reflected from the satellites would have looked like without Reyleigh scattering tossing the blue light off in all directions. Unless I am totally misunderstanding how the scattering works (always possible but in this case it don't think so!) Reyleigh could not be making a light source look more blue, it would pull blue light from the line of sight to the object and spread it around the sky, making the sky bluer at the light source less so (Sun, satellites, etc.) Is that correct?

 

[Mendel]

Compared to what the light reflected from the satellites would have looked like without Reyleigh scattering tossing the blue light off in all directions. Unless I am totally misunderstanding how the scattering works (always possible but in this case it don't think so!) Reyleigh could not be making a light source look more blue, it would pull blue light from the line of sight to the object and spread it around the sky, making the sky bluer at the light source less so (Sun, satellites, etc.) Is that correct?

Yes, but we never see light that hasn't been scattered.
So if you compare it to moon or the sun, it really depends on where they are to compare their blue-ness.

 

[Mick West]

Why are SL satellites blue when they are still in the train?

Can you show some images where they are a different color to the stars behind them?

 

[ced0412]

I posted the below in another thread and it was the first time I'd seen a train.

What's funny, and goes to show how bad our memories are, I thought they were blue. They traveled directly overhead.

Not race track but close enough:

Finally got to see a train last Sat 5/11 at about 9 EST in N Florida.

Was out looking for the solar flare event and right as going back inside here they come from the N / NW. They had an awesome green hue and if I didn't know about it I would have freaked out.

https://www.metabunk.org/threads/how-to-see-deployed-starlink-racetrack-flares.12797/post-315968

 

[Maury Markowitz]

Well it turns out all of this was explained over on SpaceWeather.

https://www.spaceweather.com/archive.php?view=1&day=25&month=08&year=2024

Can you show some images where they are a different color to the stars behind them?

Some excellent examples on that page.

 

[JMartJr]

Some excellent examples on that page.

And now they're on this page!

Recently a number of people reported sightings of particularly blue satellites. In the night of August 11, while observing the Perseids, I captured an entire series of them. It was Starlink group G9-1, launched in June. Those are DTC satellites. Apparently the material they're using to reduce brightness also gives the blue color, for which SpaceX said that it's "not unexpected".The color is visible to the naked eye and these Generation 2 Starlink satellites tend to be brighter anyway.This is a composite of 12 individual exposures. Satellite trails were 5-15 minutes apart, extracted so they don't get lost in the jungle of airplanes and other satellites. Their positions relative to the stars are accurate. The sky is a basic stack aligned in Sequator.

Source: https://www.spaceweather.com/archive.php?view=1&day=25&month=08&year=2024

 

[Maury Markowitz]

Some more wonderful blue, this time in video form:


Source: https://www.youtube.com/watch?v=JuXUWOmZ5hg