Admin. 11/21/171. Class website http://www.astro.ufl.edu/~jt/teaching/ast1002/2. Optional Discussion sections: Tue. ~11.30am (period 5), Bryant 3; Thur.

~12.30pm (end of period 5 and period 6), start in Pugh 170, then Bryant 3 [if just a small group we move to my office - 302 Bryant].

3. Office hr: today only: Tuesday 1.30-2pm; Wed. 12.30-1.00pm, Bryant 302 (but email me if coming on Wed.).

4. Homework 11: is due Wed. Nov. 29th 11.59pm via Canvas e-learning under “Quizzes”

5. Reading this week: Ch. 0-3, 4.1-4.3, 5-16, 17, 18, 4.46. Observing project deadline was Thur. Nov. 2nd 20177. Final exam - Tue. 5th Dec., in class. (about 1/2 the questions on material since midterm

2).You are NOT allowed calculators: questions will only require simple arithmetic. You will be given a list of all formulae used in the class (see next slide). Exam is multiple choice format on a scantron so bring a pencil. Bring your UF ID. In class review session on Thur. 30th Nov. - bring questions for discussion.

8. Email me Astro-news, jokes, tunes, images: ast1002_tan-l@lists.ufl.edu9. Printed class notes? Name tags?

All Formulae (for final):Speed = distance / timeAngular size: θ = size / distanceKepler’s 3rd Law: P2 = a3

[ Newton’s version of Kepler’s 3rd: P2 ∝ a3/(m1+m2) ]Newton’s 2nd Law: F = m aNewton’s Law of Gravity: F ∝ m1 m2 / r2 Density = mass / volumeVolume of a sphere = (4/3)πr3

Surface area of sphere = 4πr2

Angular momentum ∝ mass x rotation rate x size2

Frequency: f = 1/PeriodSpeed of wave (light) = frequency x wavelength: c = f λEnergy of Photon: E = h f Wien’s Law: λmax = 0.29cm / T(K) Parallax distance: d = 1/ p Flux: F = L / (4πd2)Stellar Luminosity: L = 4πr2 σT4

Doppler Shift: Δ λ / λ = v / cMain Sequence Luminosity: L ∝ M4

Light Gathering Power = Area x Exposure time Resolving Power (angular resolution) = 0.25 λ (microns) / diameter (m) Stellar lifetime ∝ M / L ∝ M-3

Mass-Energy Equivalence E = m c2

Orbits in Galaxies: Mgalaxy+ Msun ∝ a3/P2 ∝ a v2

Hubble’s Law: v = H0 dDrake Equation: Ntc = Rsf fwp Nsfl flb fil fts Lt

Key Concepts: Lecture 35:

Life in the Universe: Origin of Life

The Drake Equation

Life in the Universe– What is life?– How did life arise on Earth?– Are we alone? The Drake Equation– How common are habitable environments?– How do we find Extrasolar Planets?– The number of technological civilizations in the

Galaxy– Practicalities of communication and interstellar

travel

Definition of Life• It can react to its environment• It can grow and take nourishment from its

surroundings• It reproduces - passing along some of its

characteristic to its offspring: HEREDITY• It has the capacity for genetic change,

allowing evolution from generation to generation, mediated by Darwinian selection pressures.

Unity of Life on Earth• All living things on Earth are

composed of organic material (C, H, O, N, P, S)– Carbon is abundant and can form

complex string molecules• All life on Earth uses replicating

strings of DNA (deoxyribonucleic acid) (& RNA [Ribonucleic acid])

• These are used to construct amino acids, which link together to form more complex molecules of proteins.

The Origin of Life on Earth• Oldest surface rocks found - ~3.8 billion

years old• “Earth Sterilizing” impacts every

~100,000 years ending about 3.8 billion years ago– Rock vapor from impact circles

Earth for months– Oceans are evaporated with each

impact• First fossils: 3.8 - 3.5 billion years ago

– Archaea - cyanobacteria which can live in extreme conditions

– Archaea today in hot springs & salt ponds

Life seems to have started in <100 Million years under poor conditions

Can Life Form this Fast?• Miller-Urey experiment (1953)

– Primordial soup (Water, Methane, CO2 & Ammonia)

– Energize it with a spark (simulates lightning) or UV light (used in later versions of the experiment)

– After a few days contained many amino acids

– Not a living organism, but on the right road

Can Life Form this Fast?

• Amino acids arrange into blobs– Walls pass small molecules– More complex ones are

formed inside which cannot leave

– Structures similar to living cells but not living

• Cell-like structures can form

Panspermia• Controversial (most scientists don’t believe it is

correct) idea that life may have originated elsewhere and was brought to Earth

• Gets around problem of having life form in a hostile environment

• But life must survive in space for long periods– High gamma ray flux

History of Life on Earth

History of Life on Earth

Further reading: The Ancestor’s Tale - Richard Dawkins

• Ntc = Rsf fwp Nsfl flb fil fts Lt• Ntc = number of technological civilizations now present in Milky Way• Rsf = rate of star formation over lifetime of the Galaxy• fwp = fraction of stars with planetary systems• Nsfl = average number of planets suitable for life• flb = fraction of habitable planets where life arises• fil = fraction of life-bearing planets where intelligence evolves • fts = fraction of intelligent-life planets that develop technology• Lt = average life time of a technological civilization

The Drake Equation

Star Formation Rate of the Galaxy

• In the Milky Way galaxy stars form at the average rate of 10 stars per year

• This average is determined over the lifetime of the Milky Way: about 1011stars have formed over the last 1010years.

Fraction of stars with planets

• Theoretically we expect all stars to form with disks, where planets may form. However, star and planet formation are complicated processes and we do not yet have a way to predict how often planetary systems form.

• Therefore, we need to look for the planets!

Planets in Formation• Planetary systems are

easier to detect in formation rather than after material has gathered into planets– disks around young stars– 50% - 100% of solar-type

stars have enough mass in their disks to form planets

– what fraction actually forms planets is uncertain from just these data

– Need direct search (see next lecture)