PHYSICS 20E Lecture Notes - Lecture 23: Hard Stuff, Absorption Spectroscopy, Messier 13
Document Summary
20% of the stars in our galaxy have habitable earth-like planets. If life is common on these planets, a real chance that we will detect it in your lifetime. While we cannot yet study other earths, we can prepare by studying our own earth from the outside. In principle we can learn a lot about an exo-earth using spectroscopy. The big challenge: earths are extremely faint compared to the light of their parent stars. Sun"s spectrum is 1010 brighter than the sun. The spectrum of the earth has two components: Combined, the earth is about 2 billion times fainter than the sun. Not possible yet, but will be doable in ~20 years. One idea: use stars as flashlights to study distant planet atmospheres. A planet"s thermal infrared spectrum tells you its temperature. Earth"s spectrum can be measured from spacecraft or by reflection off the moon (earthshine) Absorption lines from different atoms and molecules in the atmosphere.
