Astronomy 101The Solar System

Tuesday, Thursday2:30-3:45 pmHasbrouck 20

Tom Burbinetomburbine@astro.umass.edu

Course

• Course Website:– http://blogs.umass.edu/astron101-tburbine/

• Textbook:– Pathways to Astronomy (2nd Edition) by Stephen Schneider

and Thomas Arny.• You also will need a calculator.

Office Hours

• Mine

• Tuesday, Thursday - 1:15-2:15pm

• Lederle Graduate Research Tower C 632

• Neil

• Tuesday, Thursday - 11 am-noon

• Lederle Graduate Research Tower B 619-O

Homework

• We will use Spark

• https://spark.oit.umass.edu/webct/logonDisplay.dowebct

• Homework will be due approximately twice a week

Astronomy Information• Astronomy Help Desk

• Mon-Thurs 7-9pm

• Hasbrouck 205

•The Observatory should be open on clear Thursdays

• Students should check the observatory website at: http://www.astro.umass.edu/~orchardhill for updated information

• There's a map to the observatory on the website.

Final

• Monday - 12/14

• 4:00 pm

• Hasbrouck 20

HW #9

• Due today

HW #10

• Due Oct. 29

Exam #2• Average was a 75

• Grades from 100s to a 27.5

• http://web.mit.edu/thb/www/exam2a.answers.doc

• Average (80% exams, 20% HW) for people who took both exams is ~81

32 Extrasolar planets were just announcedThe new alien planets, which bring the known count beyond 400, were found with the HARPS spectrograph on the European Southern Observatory's 3.6-m telescope in La Silla, Chile.

Some just five times the mass of Earth

Others five times heftier than giant Jupiter

http://www.msnbc.msn.com/id/33379852/ns/technology_and_science-space/

Radioactive Decay

http://academic.brooklyn.cuny.edu/geology/leveson/core/topics/time/graphics/radio1.gif

What are the assumptions to get an age?

What are the assumptions?

• No loss of parent atoms– Loss will increase the apparent age of the sample.

• No loss of daughter atoms– Loss will decrease the apparent age of the sample.

• No addition of daughter atoms or if daughter atoms was present when the sample formed– If there was, the age of the sample will be inflated

• These can possibly be all corrected for

Basic Formula

• Number of daughter atoms formed = number of parent atoms consumed

• If there were daughter atoms originally there

• D – Do = no - n

• Remember: n = noe-λt so no = n eλt

• D- Do = n eλt – n

• D = Do + n (eλt – 1)

Commonly Used Long-Lived Isotopes in Geochronology

Radioactive Parent (P)

Radiogenic Daughter

(D)

Stable Reference

(S)

Half-life, t½

(109 y) 

Decay constant, l

(y-1)

40K 40Ar  36Ar 1.25 0.58x10-10

87Rb 87Sr 86Sr 48.8 1.42x10-11

147Sm 143Nd 144Nd 106 6.54x10-12

232Th 208Pb 204Pb 14.01 4.95x10-11

235U 207Pb 204Pb 0.704 9.85x10-10

238U 206Pb 204Pb 4.468 1.55x10-10

How do you determine isotopic values?

How do you determine isotopic values?

• Mass Spectrometer

It is easier

• To determine ratios of isotopic values than actual abundances

Example

• 87Rb 87Sr + electron + antineutrino + energy

• Half-life is 48.8 billion years

• 87Sr = 87Srinitial + 87Rb (eλt – 1)

• Divide by stable isotope

• 87Sr = 87Srinitial + 87Rb (eλt – 1)

86Sr 86Sr 86Sr

Example

• Formula for line

• 87Sr = 87Srinitial + (eλt – 1) 87Rb

86Sr 86Sr 86Sr

y = b + m x

http://www.asa3.org/aSA/resources/wiens2002_images/wiensFig4.gif

= (eλt – 1)

Carbon-14

• 99% of the carbon is Carbon-12

• 1% is Carbon-13

• 0.0000000001% is Carbon-14

• The half-life of carbon-14 is 5730±40 years.

• It decays into nitrogen-14 through beta-decay (electron and an anti-neutrino are emitted).

• Due to Carbon-14’s short half-life, can only date objects up to 60,000 years old

• Plants take up atmospheric carbon through photosynthesis

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html

• When something dies, it stops being equilibrium with the atmosphere

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html

Why is Carbon-14 still present if it has such a short half-life?

Why is Carbon-14 still present if it has such a short half-life?

• Cosmic rays impact Nitrogen-14 and create Carbon-14

• Cosmic rays are energetic particles (90% are protons) originating from space. From the Sun (solar cosmic rays) or outside the solar system (galactic cosmic rays)

• n + 14N → 14C + p

• http://en.wikipedia.org/wiki/Image:Radiocarbon_bomb_spike.svg

Composition of the Planets

Different bodies have different densities• Density = Mass/Volume

• M = 42d3/GP2 V =4/3R3

Life of a Star

• A star-forming cloud is called a molecular cloud because low temperatures allow Hydrogen to form Hydrogen molecules (H2)

• Temperatures like 10-50 K

Region is approximately 50 light years across

Condensing

• Interstellar clouds tends to be lumpy

• These lumps tend to condense into stars

• That is why stars tend to be found in clusters

Protostar

• The dense cloud fragment gets hotter as it contracts

• The cloud becomes denser and radiation cannot escape

• The thermal pressure and gas temperature start to rise and rise

• The dense cloud fragment becomes a protostar

When does a protostar become a star

• When the core temperatures reaches 10 million K, hydrogen fusion can start occurring

Formation of Solar System

• Solar Nebula Theory (18th century) – Solar System originated from a rotating, disk-shaped cloud of gas and dust

• Modern theory is that the Solar System was born from an interstellar cloud (an enormous rotating cloud of gas and dust)

Composition

• ~71% is Hydrogen

• ~27% is Helium

• ~2% are other elements (Fe, Si, O) in the form of interstellar grains

• Show animation

• Dust grains collide and stick to form larger and larger bodies.

• When the bodies reach sizes of approximately one kilometer, then they can attract each other directly through their mutual gravity, becoming protoplanets

• Protoplanets collide to form planets– Asteroids such as Ceres and Pallas are thought to be

leftover protoplanets

• Condensation – conversion of free gas atoms or molecules into a liquid or solid

• Volatile – Elements or compounds that vaporize at low temperatures

Show animation

Form atmosphere and oceans

Show animation

Any Questions?