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1 Lo

2 Explanation: Comet Lovejoy was captured last week passing well in front of spiral galaxy M63. Discovered only three months ago and currently near its maximum brightness, Comet Lovejoy can be seen near the Big Dipper from dark northerly locations before dawn with the unaided eye. An unexpected rival to Comet ISON, C/2013 R1 (Lovejoy), pictured above, is currently sporting a large green coma and a beautifully textured ion tail. Comet Lovejoy is now headed back to the outer Solar System but should remain a good sight in binoculars for another few weeks. Conversely, spiral galaxy M63, lies far in the distance and is expected to remain stationary on the sky and hold its relative brightness for at least the next few million years.

3 Today All things due Take home quiz Expanding universe Lab The Big Bang and ET!!! Weekly Schedule Next Tuesday (12/10) Final 2:30pm- 4:30pm

4 Hubble s Law: the further away a galaxy is, the faster it recedes Hubble found that most every object that he could see was moving away from every other object. The farther away an object (galaxy), the faster it was moving away (the greater the redshift).

5 An expanding universe Hubble s Law: velocity= H 0 x distance Since v=d/time; time= 1/H H 0= D to a galaxy and its velocity v time=~14 billion years

6 Formation of the solar system The Big Bang Theory our universe began with a primordial explosion some 13.7 billion years ago Marks the beginning of space and time Video

7 An expanding Universe? When did it all begin? The Big Bang: all mass and energy in a single point It exploded ~13.7 Ga and has been expanding ever since. Big Bang Fig. 1.5b

8 Aftermath of the Big Bang Researchers have developed a model of the Big Bang. During the first instant, only energy no matter was present. Started as a rapid cascade of events. Hydrogen atoms within a few seconds At 3 minutes, hydrogen atoms fused to form helium atoms. Light nuclei (atomic no. < 5) by Big Bang nucleosynthesis The Universe expanded and cooled. Fig. 1.5b

9 With expansion and cooling, atoms began to bond. After the Big Bang Hydrogen formed H 2 molecules the fuel of stars. Atoms and molecules coalesced into gaseous nebulae. Gravity caused collapse of gaseous nebulae. Collapse resulted in increases in: Temperature. Density. Rate of rotation.

10 Evidence of The Big Bang Continuing expansion of the universe Measured cosmic background radiation Measurements of element abundances

11 The Big Bang Cosmic Microwave Background (CMB): The figure below shows the temperature of the CMB at every point in space. The uniformity of the CMB means that at some point in time all the matter in the universe was very close together.

12 The Big Bang Relative Abundance of Light Elements Scientists predict that if the Big Bang occurred, there would not have been enough time to form any heavy elements due to the rapidly expanding universe; only hydrogen and helium could have been formed. 75% of all the matter in the universe is hydrogen and about 25% is helium. (Heavy elements make up less than 1%)

13 18.1 Cosmic Evolution Simple one-celled creatures, such as algae, appeared on Earth about 3.5 billion years ago. More complex one-celled creatures, such as the amoeba, appeared about 2 billion years ago. Multicellular organisms began to appear about 1 billion years ago. The entirety of human civilization has been created in the last 10,000 years.

14 Drake equation estimates the number of detectable extraterrestrial civilizations in the Milky Way galaxy

15 Definition of life As a group come up with 5-7 factors that everyone agrees with that defines life. It should clearly show that rocks are not alive and that plants are alive. According to your definition, are stars alive? Compare and contrast your group s definition with that from another group.

16 18.1 Cosmic Evolution These are some generally agreed-upon characteristics that any life-form should have: Ability to react to environment Ability to grow by taking in nourishment and processing it into energy Ability to reproduce, with offspring having some characteristics of parent Ability to evolve

17 18.2 Life in the Solar System Life as we know it: Carbon-based, originated in liquid water Is such life likely to be found elsewhere in our Solar System? Best bet: Mars. Long shots: Europa, Titan. Other places are all but ruled out.

18 18.2 Life in the Solar System What about alternative biochemistries? Some have suggested that life could be based on silicon rather than carbon, as it has similar chemistry. Or the liquid could be ammonia or methane rather than water. However, silicon is much less likely to form complex molecules, and liquid ammonia or methane would be very cold, making chemical reactions proceed very slowly.

19 18.3 Intelligent Life in the Galaxy The Drake equation, illustrated here, is a series of estimates of factors that must be present for a long-lasting technological civilization to arise.

20 The Drake equation The Drake Equation is listed on page 493 in your text. Independently, each person in your group should estimate the average lifetime of a technologically competent civilization as described in the Drake equation. Explain the variation of the values your group had.

21 18.3 Intelligent Life in the Galaxy

22 18.3 Intelligent Life in the Galaxy The rate of star formation: 10 stars per year (dividing population of Milky Way by its present age) Fraction of stars having planetary systems: Most planetary systems like our own have not been detected yet, but we would expect to be able to detect them using current methods. We expect most start systems to have formed planets as well, and assign this factor a value near 1.

23 Habitable zone Fraction of habitable planets on which life actually arises: Experiments suggest that this may be quite likely; on the other hand, it might be extremely improbable! We ll be optimistic, and give this factor a value of one.

24 We ll give this factor a value of one also. Fraction of life-bearing planets where intelligence arises: Here we have essentially no facts, just speculation and opinion. We ll continue being optimistic, and assign this factor a value of one. Fraction of planets where intelligent life develops and uses technology: Again, we have no facts, but it does seem reasonable to assume that intelligent life will develop technology sooner or later.

25 18.3 Intelligent Life in the Galaxy So, right now the first six factors, as we ve assigned values to them, give / Therefore:

26 18.3 Intelligent Life in the Galaxy For the average lifetime of a technological civilization, we can t even use ourselves as an example our civilization has been technological for about 100 years, but who knows how long it will last? Also, we assigned a value of one to several very uncertain factors; even if only one of them is low, the number of expected civilizations drops quickly.

27 If the average lifetime of a technological civilization is 1 million years, there should be a million such civilizations in our Galaxy, spaced about 30 pc, or 100 ly, apart on average. This means that any two-way communication will take about 200 years (if there is in fact a technological civilization 100 light-years or less away from us).

28 18.4 The Search for Extraterrestrial Intelligence We have already launched interstellar probes; this is a plaque on the Pioneer 10 spacecraft.

29 18.4 The Search for Extraterrestrial Intelligence We are also communicating although not deliberately through radio waves emitted by broadcast stations. These have a 24-hour pattern, as different broadcast areas rotate into view.

30 18.4 The Search for Extraterrestrial Intelligence If we were to deliberately broadcast signals that we wished to be found, what would be a good frequency? There is a feature called the water hole around the radio frequencies of hydrogen and the hydroxyl molecule. The background is minimal there, and it is where we have been focusing many of our searches.

31 18.4 The Search for Extraterrestrial Intelligence These are the telescopes of Project Phoenix, designed to search for extraterrestrial signals. At left is a simulation of an actual signal; none has ever been found.