Astronomy 100 Tuesday, Thursday 2:30 - 3:45 pm Tom Burbine

PRS and HW grades 100% PRS and 100% HW scores will bring up a person’s total exam score by ~4-6 points

A A – B – B – B – C – C – C – D – D – D – F below If the class average is 80% or higher, the grade distribution will be something like this

Schedule May 3 (Does Life Exist Elsewhere in the Universe) May 5 (Review) May 10 (Exam 4) May 12 (Exam 5) (optional) May 20 (Final) (optional)

Exam 4 Know the class notes Know all the definitions on the website Know the Summary of Key Concepts at the end of every chapter

Exam 5 and Final Know the class notes Know how to do every question on the 1 st 4 exams Know the Summary of Key Concepts at the end of every chapter

Homework Assignment (Due Today) Make up a test question for next test Multiple Choice A-E possible answers 1 point for handing it in 1 point for me using it on test The question needs to be on material that will be on the 4th exam

Homework Assignment (Due Thursday) I have placed 40 terms on the website You get 0.1 of a HW point for each of these you define and hand in to me Definitions need to be hand-written or hand-typed A lot of these definitions will be on next test

Drake Equation Dark Energy Tully-Fisher Relation ALH84001 Cepheid Variable White Dwarf Jocelyn Bell Viking Mission Hubble’s Law SETI Big Bang COBE Standard Candle Quasar Planck Time Inflation in the Early Universe Olber’s Paradox Cosmic Microwave Background Isotope Baryon Percival Lowell Redshift Dark Matter MACHO Critical Density Radio Galaxy Main Sequence Fitting Cosmological Horizon White Dwarf Supernova Interstellar Medium Supercluster WIMP Pulsar Habitable Zone Maunder Minimum Convection Zone Radiation Zone Hubble’s Constant Starburst Galaxy Europa

Astronomy Help Desk There is an Astronomy Help Desk in Hasbrouck 205. It is open Monday through Thursday from 7-9 pm.

Dark Energy The universe appears to be accelerating (expanding faster) Dark Energy is proposed as the cause Pushing galaxies apart

Basic Definition of Life Growth Metabolism Motion Reproduction Stimulus response

Percival Lowell ( ) Lowell produced intricate drawings of the Red Planet Finding hundreds of straight lines (termed "canals")

He thought Lowell concluded that the bright areas were deserts and the dark were patches of vegetation Lowell thought the canals were constructed by intelligent beings who once flourished on Mars.

For years People thought life could exist on Mars and Venus, the closest planets to Earth

However, Venus is extremely hot (~ K) Atmospheric pressure is 90 times that of Earth

Mars The average recorded temperature on Mars is -63 °C with a maximum temperature of 20 °C and a minimum of -140 °C Atmospheric pressure is 1/100 of Earth’s

In the past Mars appeared to be warmer and wetter

ALH84001 Allan Hills Martian meteorite found in Antarctica Thought to have evidence for life

Evidence organic molecules Magnetite that looks like it formed from biologic activity nanofossil-like structures

Key to Life All life on Earth depends on water So if you find water, you may find life

Habitable Zone The region around a star in which planets could potentially have surface temperatures which liquid water could exist

Viking Missions Missions to Mars in 1976 to look for Life Two Missions to Mars to look for Life

Experiments Three of the four experiments to look for life produced positive results But results could all be explained through non- biologic chemistry

Pyrolytic-Release (PR) experiment A mixture of radioactive CO 2 and CO was introduced into a vessel containing a soil sample Sample was irradiated with light Then gases flushed out Heated Detector measured radioactive carbon compound given off from heating Probably due to non-biologic reactions in soils and not life

SETI Search for Extraterrestrial Intelligence Search for signals from other civilizations

Drake Equation Calculates how many civilizations are out there in our galaxy now

Version of Formula Number of civilizations that exist today = the number of habitable planets in the galaxy times the fraction of planets that have life in the galaxy times the fraction of the life-bearing planets in the galaxy upon which a civilization capable of interstellar communication has at some time arisen times the fraction of all civilizations that have existed in the galaxy that exist now

Number of habitable planets 100 billion?

Fraction of Planets that have life in the Galaxy ?

Fraction of the Life-Bearing Planets in the Galaxy upon which a Civilization capable of interstellar communication has at some time arisen ?

Intelligent Life Intelligent life that we can detect is usually defined as life that can build a radio telescope

Radio Transmitting information over radio waves is very cheap uses equipment that is easy to build has the information-carrying capacity necessary for the task The information also travels at the speed of light.

Fraction of all civilizations that have existed in the galaxy that exist now ?

Fermi’s Paradox Where are they?

Fermi’s Paradox Why have we not observed alien civilizations even though simple arguments would suggest that some of these civilizations ought to have spread throughout the galaxy by now?

Reason for question Straightforward calculations show that a technological race capable of interstellar travel at (a modest) one tenth the speed of light ought to be able to colonize the entire Galaxy within a period of one to 10 million years.

Explanation Interested in us but do not want us (yet) to be aware of their presence (sentinel hypothesis or zoo hypothesis)

Explanation Not interested in us because they are by nature xenophobic or not curious

Explanation Not interested in us because they are so much further ahead of us

Explanation Prone to annihilation before they achieve a significant level of interstellar colonization, because: (a) they self-destruct (b) are destroyed by external effects, such as: (i) the collision of an asteroid or comet with their home world (ii) a galaxy-wide sterilization phenomenon (e.g. a gamma-ray burster (iii) cultural or technological stagnation

Explanation Capable of only interplanetary or limited interstellar travel because of fundamental physical, biological, or economic restraints

Questions