ASTR 101 Lecture Notes - Lecture 38: Interstellar Travel, Radiant Energy, Arecibo Observatory

• School: Queen's University
• Department: Physics, Engineering Physics and Astronomy
• Course: ASTR 101
• Professor: David Alan Hanes

Document Summary

Problem to active approaches: they take time and may not yield a result for many centuries at least. We"ve been communicating our presence on earth ever since the invention of fire. Our light leaks out into space, travelling at the speed of light. Problem: our visible glow" is feeble next to the sun: we won"t be seen. (like looking for a firefly next to a flashlight) Can improve contrast by working in other wavelengths. Our radio broadcasts leak" out into space, at wavelengths where the sun is quiet". Detectable signals would vary due to earth"s rotation. Importance of variability: a continuous glow" at any wavelength is undistinguished, and could be from a natural source (a star, a cloud of gas, etc. ). Radiation that is highly modulated (that is, changing rapidly and in complex ways) draws attention to itself and probably has a non-natural origin. Have been flowing out into space for 60 years.