Would Earth not be seen flashing from space like a lighthouse?

[earthlingjeff]

TL;DR Summary

Earth Lighthouse

Can anyone tell me if this would be correct? Would Earth not be seen flashing from space like a lighthouse to a distant planet when it reflects oceans and then DMS as the sons reflection per perspective travels across land then back to Ocean then back to land?

I'm sure it probably says that somewhere but I've never heard.

Thank you very much

 

[jedishrfu]

I think it will appear as a bright spot in the distance not flashing like a lighthouse light might much as we see Mercury, Venus, Mars, Jupiter or Saturn.

https://earthobservatory.nasa.gov/collection/1658/earth-from-afar

and here's the farthest photo of Earth we have so far:

https://mashable.com/article/earth-pictures-images-from-space

 

[russ_watters]

Earth, like the rest of the planets in the solar system we can see from Earth, does not reflect light like a disco ball (a ball of mirrors). The reflections go in all direction, so you can see the entire side of the planet facing you, even the parts not directly facing.

 

[Baluncore]

Welcome to PF.

Viewed from another planet in the solar system, the variation in cloud cover would be noticed. The specular reflections from the ocean surface would be confused by the water waves.

Since the Earth is close to spherical, it will reflect and scatter sunlight in all directions, not like a flat mirror or Earth.

Viewed from outside the solar system, the brightness of the Sun would dominate the variations in brightness of the Earth.

 

[earthlingjeff]

Earth, like the rest of the planets in the solar system we can see from Earth, does not reflect light like a disco ball (a ball of mirrors). The reflections go in all direction, so you can see the entire side of the planet facing you, even the parts not directly facing.

What if you were an alien measuring the intensity of light from distant stars and planets with vary from time to time and not seem like a constant

 

[Janus]

TL;DR Summary: Earth Lighthouse

Can anyone tell me if this would be correct? Would Earth not be seen flashing from space like a lighthouse to a distant planet when it reflects oceans and then DMS as the sons reflection per perspective travels across land then back to Ocean then back to land?

I'm sure it probably says that somewhere but I've never heard.

Thank you very much

It's a bit more complicated than that. The two areas (ocean and land) have different types of reflection, specular and diffuse.
For water, you have specular, which means that the light hitting that part of the surface not directly facing you is reflected away, and you mostly see a small specular highlight.

Land has diffuse reflection, and light is scattered more upon reflection, meaning it looks more evenly lit.

In the above images, I used a darker shade of green for land, and it still looks brighter overall than the oceans.
The end result is that the albedo( the amount of light reflected) for the ocean is 0.05-0.1, while for land, it is 0.1-0.4. In other words, land would reflect more total light than ocean.
Cloud cover, also diffuse, covers roughly 2/3 of the total surface, and ~90% of the oceans. This makes up for a great deal of the albedo difference between ocean and land areas.
The upshot is that you'd see only tiniest of variation( if any) in the Earth's brightness as it rotates.

 

[Baluncore]

What if you were an alien measuring the intensity of light from distant stars and planets with vary from time to time and not seem like a constant

Planets about other stars do not reflect sufficient light from their star to be seen from Earth. The planet's brightness may also change throughout their year, as they wax and then wane. The way we detect planets orbiting other stars is done when the planet eclipses their star's light, so we see short drops in the star's brightness. The brightness of a star blinds us to direct view of the surrounding planets.

 

[berkeman]

TL;DR Summary: Earth Lighthouse

Would Earth not be seen flashing from space like a lighthouse to a distant planet

The closest thing I can think of to a "lighthouse" effect that might be detectable would be the uplink RF comm beams to satellites. The ones to geostationary satellites are probably the strongest, since they need to travel farther to hit their targets. They are narrowband, so if a civilization on another planet not too far away were searching for other civilizations, it would be logical for them to observe other solar systems with narrowband RF receivers to improve the Signal/Noise ratio of their observations...

https://www.esa.int/Applications/Connectivity_and_Secure_Communications/Satellite_frequency_bands

Edit/add -- the first geostationary satellite for Earth was launched in 1964, so we've been doing this "lighthouse" beaming for close to 60 years now. A blink of an eye in Astronomical terms...

https://en.wikipedia.org/wiki/Geosynchronous_satellite

 

[Baluncore]

A scorching 2,000 degrees Celsius world, where metal clouds rain drops of titanium has been designated as the most reflective planet ever observed outside our Solar System by astronomers.

First discovered in 2020, the Neptune-sized planet called LTT9779b orbits its star in just 19 hours.

https://www.abc.net.au/news/2023-07...-identify-most-reflective-exoplanet/102584928

 

[Janus]

As a historical side note: In the early days after Pluto's discovery, and when it was still just a fuzzy dot in telescopes, there was a question as to why it was so small. They even considered the possibility that it was larger, but was an icy world with a relatively smooth surface, and what we were seeing was the specular highlight glinting off of it.