Phil PlaitFeb 20

In other news…

This was fun: a reader asked if aliens were in a galaxy 66 million light-years away, how big a telescope would they need to see dinosaurs on Earth?

Guess!

No; bigger. Try again. Nope, still bigger. Third try? Nope. Way, WAY bigger.

https://www.scientificamerican.com/article/could-aliens-in-another-galaxy-see-dinosaurs-on-earth/

Could aliens in another galaxy see dinosaurs on Earth?

How big would a telescope need to be to see Earth’s dinosaurs from 66 million light-years away? Think big—and then think bigger

Scientific American
Show threadRay McCarthy
@badastro
short answer:
Impossible.
I've done sums for RF, being originally a Communications Engineering Engineer.
We can maybe spot evidence of industrialisation via planet transiting star (very powerful TX) using Spectroscopic analysis.
Getting radio transmissions or seeing a city? No. Not even for neighbours in our Galaxy.
Feb 20 at 6:51pmWeb
Show threadMichael BuschFeb 20

@raymaccarthy @badastro

I am personally responsible for radio transmissions that would be detectable to our current telescopes at distances of tens of thousands of lightyears.

But only if a hypothetical alien watcher should happen to be looking in the right direction at exactly the right time.

Taking pictures of dinosaurs is many orders of magnitude harder.

Show threadRay McCarthyFeb 20
@michael_w_busch
What power, frequency & aerial/dish gain your end? Even 10 ly would be amazing.
Show threadMichael BuschFeb 20

@raymaccarthy

The Arecibo planetary radar ran at 900 kilowatts of 2380 MHz on a 300 m dish.

The Goldstone Solar System Radar is 450 kilowatts of 8560 MHz on a 70 m dish.

The range limit is set by the bandwidth, which we can control down to <0.01 Hz.

Show threadRay McCarthyFeb 20

@michael_w_busch Thanks.

Sad about Arecibo.

I'll do sums later. I used to be paid to do terrestrial link and Geosat link budgets on 920 MHz to 22 GHz.