AST Exam 1

Aaaaaagghhh

How do we define extraterrestrial life? What are we looking for?

Life beyond Earth; life that doesn’t originate from Earth

Looking for any sign of life- be it simple, complex, or intelligent

Is the universe a rational place?

Yes. The universe acts UNIFORMLY and RATIONALLY

Are there worlds beyond the solar system?

Yes, exoplanets, which are planets orbiting a star that isn’t our sun

How do we define a habitable world?

We’re asking whether it offers environmental conditions under which life could arise or survive, not whether it actually harbors life…

• First requirement is WATER!

  • The moon, venus, mars

  • Liquid water is present on or in “select” planets, but several moons, too!

• LIQUID WATER ON THE SURFACE

• VOLCANISM

• PLATE TECTONICS

• MAGNETIC FIELD

What is geocentrism?

Basically just the belief that Earth is the center of the universe, and the sun the moon and the stars all revolve around it

What is the history of geocentrism?

Ok

So,

• ancient greeks try to put system of rules together, relied partly on observations and want to explain the rising and setting of the sun, moon, planets, and stars

• they produced the 1st scientific model of the universe: GEOCENTRIC MODEL

• Aristotle supported it, argued that the Earth was at the center because it was heavy and unmoving- his student Ptolemy developed geocentric model called Ptolemaic system

  • PTOLEMAIC MODEL:

    • Retrograde motion isn’t simple and requires orbits-on-orbits (epicycles)

    • High precision prediction requires orbits-on-orbits-on-orbits

    • Makes pretty good predictions (within about 1-2 degrees)

• Geocentricism then basically ended with Nico Copernicus, as he presented the heliocentric model… GALILEO AND KEPLER later provided evidence to confirm this, which led to the gradual abandonment of geocentricism

What are the pros of geocentrism?

• essential for understanding the history of astronomy

• highlights evolution of scientific thought, showing how science corrects itself over time

What is the history of heliocentrism?

• Aristarchus of Samos (310-230 BCE)

  • Determined relative sizes of the Earth, Sun, and Moon

  • He also produced a simpler heliocentric model… if a smaller moon orbits Earth, then a smaller Earth likely orbits the sun

  • Earth is on an orbit (moving), which is a big deal that’s going to need proof

    • PARALLAX SHOULD EXIST. BUT IT ISN’T OBSERVED, SO HELIOCENTRICITY IS WRONG

    • Copernicus Revolution: Nicholas Copernicus (1540)- REVIVES HELIOCENTRICITY

      • Tycho Brache (1580ish)- made the most precise naked eye observations of planetary positions

        • Accurate to 21/60th of a degree (about 0.017 degree), sun angular diameter of about 0.5 degree, parallax of proxima cen (0.77 arcsec) 

        • Johannes Kepler (1650): Using tycho’s model and discovered that the helio model works best

What prevented heliocentrism from being quickly accepted?

• Opposition to established beliefs

• Galileo and church and stuff

What is a parallax

Wha are Kepler’s Laws of Planetary Motion?

1. Planets orbit in ellipses, not circles

2. Planets’ orbital speeds vary

3. Larger orbits have slower speed- longer orbital periods

What is aphelion?

A planet’s farthest point away from the sun

What is perihelion?

A planet’s closest point to the sun

Average of a planet’s perihelion and aphelion distances = the length of its semimajor axis (planet’s average distance from the Sun)

What is a look-back time?

Amount of time that has passed since the light from a distant object was emitted

What is the sun’s look-back time?

8.3 mins

What is the circumference of the Earth?

about 1/7th of a second (at light speed)

How long is a trip to the moon?

1.25 seconds

Sun is about 4,000 times further away from us than the moon is

how far away is pluto

about 5.5 hours away (at light speed)... 330 minutes and 11 hour orbit

What is an element defined by

the number of protons

what is an element

atoms with the same amount or number of protons

what is an isotope

• same number of protons, but different number of neutrons

what is an atomic #

 the number of protons

what is an atomic mass #

the number of protons and neutrons

what is an ion

an atom with a non-zero net charge

what do Organic molecules contain

Organic molecules contain carbon (and usually also hydrogen)

what is a molecule

2 or more atoms that are bonded together

what is a compound

molecules that are made from atoms of 2 or more atoms

what are the 3 types of spectra

continuous spectrum, absorption spectrum, and emission spectrum

what is continuous spectrum produced by

Is produced when light contains a broad and uninterrupted range of wavelengths or colors

• Emission from hot dense objects

• Blackbody radiation- hotter objects appear more blue and cooler ones emit less and appear more red

• There’s no gaps between wavelengths

what does continuous spectrum tell us

• TEMPERATURE… hotter objects emit more blue light (shorter wavelengths), while cooler objects emit more red light (longer wavelengths) aka blackbody radiation

• Luminosity and size 

  • Tells us about the temperature and energy output of dense, hot objects like stars.

what is absorption spectrum produced by

• Light source

• Gas in the way

• Electron excitation

The absorption spectrum is produced when light passes through a cooler gas, causing certain wavelengths (colors) of light to be absorbed by the atoms or molecules in the gas. This process creates dark lines, called absorption lines, in the continuous spectrum of the light.

what does absorption spectrum tell us

• Chemical composition of gasses

• Surface conditions of stars

• Movement

• Exoplanet atmospheres

  • Reveals the chemical composition, temperature, movement, and conditions of the cooler gas surrounding hot objects, like a star's atmosphere or an exoplanet’s atmosphere.

what is emission spectrum produced by

• When atoms or molecules emit light at specific wavelengths. This happens when an atom's electrons move from a higher energy level to a lower one, releasing energy in the form of light.

  • Excitation

  • Electron decay

  • Wavelength of light

what does emission spectrum tell us

• Chemical composition of gasses

• Temperature and density

• Nebulae (gas clouds) and stellar formation

  • Provides information about the composition, temperature, and density of hot, low-density gases, like nebulae or stellar atmospheres.

what are the 2 types of planets?

• 1. Near to the sun

  • Mercury, venus, earth and mars (MVEM)

    • 4 terrestrial (solid and dense) planets

    • Solid surfaces with no or very few moons

• 2. Farther from the sun

  • Jupiter, saturn, uranus, and neptune (JSUN)

    • Gas giants/jovian planets/ice giants

    • No solid surfaces with many moons… H, He

Characteristics of asteroids

Asteroids are basically chunks of rock and metal that orbit the sun but are much smaller than planets

Characteristics of meteors

typically made up of rocks, metal, or a combination of the two

How is the universe “moving” ?

Gravity and gravitational forces/pull

How do stellar lifetimes change?

Stars do not last forever.They are born, live, and die.A star is“born”when hydrogen fusion begins in its central core, and it lives as long as it can generate energy through fusion. A star “dies”when it finally ceases to produce energy by any kind of fusion.

How do stellar masses change?

• Spend most of their lives fusing hydrogen into helium

Rock types and how they form/change

• Igneous, sedimentary, metamorphic 

• Also split into silicates and carbonates

• Layering of different rocks gives us this record- younger rocks are near the surface and are increasing age with depth

• Fossils embedded in the geological record- gives us an understanding of the history of life on Earth

• Rocks allow reconstruction of Earth’s surface history- allows us to look over a 46 year old “geological record”

What is radiometric dating

The most reliable method for measuring the age of a rock, fossil, or other solid object… relies on careful measurement of an object’s proportions of various atoms and isotopes

Idea is to determine the age of a rock or something from the ratio of parent and daughter nuclei within it, which depends only on the DECAY RATE and LENGTH OF TIME over which he decay has been occurring

Is governed by the laws of quantum physics

what is alpha decay

Large atomic nucleus ejects a helium nucleus, which consists of 2 protons and 2 neutrons

what is Beta decay/electron capture

Nucleus emits or absorbs an electron, causing one of its neutrons to turn into a proton, or a proton to turn into a neutron

what is a half-life?

The TIME IT TAKES FOR HALF OF PARENT TO DECAY INTO DAUGHTER; time it would take for half the atoms in a sample of the substance to decay

What has radiometric dating told us?

• OLDEST INTACT ROCKS: 4.02GYRS

• OLDEST EARTH ROCK FRAGMENTS (ZIRCON CRYSTALS): 4.38GYRS

• Age of the solar system: about 4.5 billion

What are decay rates known for?

Many isotopes

What happened during the Hadean Eon?

1. The atmosphere is built by these volcanoes/arise from volcanic eruptions

2. Outgassing of trapped gasses

   1. Massive amounts of H20 and CO2 are given off during volcanic eruptions… as well as N2, H2, H2S, SO2

3. So, the atmosphere builds up and water vapor condenses

4. water vapor turns into rainfall- causes oceans and lakes to fill up

5. H2O leaving behind a CO2 dominated atmosphere, which leads to high temperatures

6. Surface of Earth undergoing bombardment (ended about 3.8Gyrs ago)

Ultimately, there’s reason to believe that life started at the end of the Hadean Era

• in the process of all of this, the surface is continually reshaped by VOLCANISM, PLATE TECTONICS, AND EROSION

In the process and events of the Hadean Ion, what is the surface continually reshaped by, and what are these things driven by?

• in the process of all of this, the surface is continually reshaped by VOLCANISM, PLATE TECTONICS, AND EROSION

  • All of these are driven by the planet’s internal heat- Earth’s internal structure reflects this

    • All internal Earth must have been molten at some point

What are the original heat sources?

• gravitational energy

• radioactivity

• impacts

  • Why it worked:

    • Ongoing radioactivity and good insulation (Mars has much less “stuff” (thermal energy/mass than Earth does), which is why they aren’t Earth

    • Residual heat drives gravitational energy, which leads to this ongoing radioactivity and good insulation

What was the atmosphere like during/in the Hadean Era

• Volcanic gasses

• lack of oxygen

• water vapor

• high pressure

• temperature

How old is the continental crust?

• 4 billion years old

• Continental crust (granite) is always floating, granite gets deformed and rearranged, and slowly grows and is added to

How old is the seafloor crust? (basalt- igneous)

• Is very young and has very young material (200 million years old)

• Is like a conveyor belt

• Seafloor is created and destroyed

How is the magnetic field made

• The liquid outer core of the Earth generates the magnetic field

• Magnetic field is created whenever an electric charge is in motion

What does the magnetic field do?

• Forms a protective barrier, which protects the atmosphere from erosion by solar wind particles

• protects the surface against bombardment by high-energy particles

Keeping/maintaining an atmosphere- what does gravity do?

Keeps constant pull on planets in atmosphere

What is solar wind stripping?

Solar wind stripping is the process by which the solar wind removes gas from a planet’s atmosphere over time

• refers to process where charged particles' from the Sun’s solar wind directly interact with and strip away atmospheric particles

  • PARTICULARLY IMPACTS PLANETS WITH WEAK MAGNETIC FIELDS

What is thermal escape?

loss of atmospheric particles due to high temperatures, where molecules gain enough energy from heat to be able to escape velocity and leave the planet’s gravitational pull

• Occurs when atmospheric molecules gain enough kinetic energy due to high temperatures, ALLOWING THEM TO REACH ESCAPE VELOCITY AND LEAVE THE PLANET’S ATMOSPHERE

Search for Extraterrestrial Intelligence is…

Search for intelligent, communicating civilizations

what does astrobiology focus on?

• 1. Studying the conditions conducive to the origin and ongoing existence of life

• 2. Looking for these conditions on other planets in our solar system and around other stars

• 3. Looking for the occurrence of life elsewhere

What did Anaximander do

• Earth is surrounded by the celestial sphere

• The sun and the stars are placed on the sphere, moving around the Earth

• Was successful at explaining MOST astrological phenomenon, except for planets

• Sun, moon, and the planets are all on their own spheres (circles) centered on Earth 

  • You can’t change from a circle (perfect) 

  • Their orbital velocity thus cannot be changed

• Assumption = Earth is centered, there are circular orbits and constant/consistent/uniform speeds

What did Aristarchus of Samos 310-230 BCE do

• Determined relative sizes of Earth, Sun, and Moon

• He also produced a simpler heliocentric model… if a smaller moon orbits Earth, then a smaller Earth likely orbits the sun

What did Tycho Brache do?

made the most precise naked eye observations of planetary positions

• was accurate to about 21/60th of a degree

Who, using Tycho’s model, discovered that the helio model works best?

Johannes Kepler

What did Galileo do?

• First person to use telescope

• His telescope observations point to the helio model, starts understanding the physics of motion

  • Observes: moon orbiting jupiter, phases of venus, Galileon satellites

What did Newton do?

• Discovers physical principles behind kepler’s laws and mathematically describes them

• 3 laws of motion

• first to realize an attractive force could explain multiple phenomena

• FOUND THAT STRENGTH OF FORCE DEPENDS ON MASSES AND SEPARATION (DISTANCE)

  • Fg = G

• Inverse square law

• Successfully predicts comet orbits and the existence of Uranus 

What are Newton’s 3 laws of motion?

1. Law of Inertia (First Law): An object at rest stays at rest, and an object in motion stays in motion with a constant velocity unless acted upon by an external force

2. Law of Acceleration (Second Law): The force acting on an object is equal to its mass multiplied by its acceleration (F = ma)

3. Law of Action and Reaction (Third Law): For every action, there is an equal and opposite reaction

What did William of Ockham do

• Says that entities must not be multiplied beyond necessity 

• Idea of simplicity also goes back to Aristotle and his student Ptolemy