Learning Goals: I will: 4. Complex Knowledge: demonstrations of learning that go aboveand above and beyond what was explicitly taught. 3. Knowledge: meeting the learning goals and expectations. 2. Foundational knowledge: simpler procedures, isolated details, vocabulary. 1. Limited knowledge: know very little details but working toward a higher level. I will: understand the properties of different types of galaxies. understand how the universe came to be what we observe today. understand how astronomers use astronomical objects (standard candles) Understand how we use a distance ladder to estimate the size of the universe and to measure large distances in the universe. understand how astronomers determine the age and size of the universe?.

YOU HAVE TWO FYI’S TODAY! I’M COMING AROUND TO CHECK YOUR FOLDABLES!

Question of the day How does Hubble's law help determine distances to the most remote galaxies?

Redshift of Spectral Lines Which color of visible light has the longest wavelength? Which color of visible light has the shortest wavelength?

The Doppler Effect change in frequency of a wave for an observer moving relative to the source of the wave. compared to the actual emitted frequency, received frequency is: higher during the approach, identical at the instant of passing by, lower during the recession.

Not Just Sound

Sun Distant Supercluster If you know how redshifted an object’s spectrum is, you know how fast it is moving away from you

Hubble Diagram Hubble used Cepheids and type 1a supernovae to calculate the distance to thousands of galaxies He used their spectrum to calculate the velocity at which those galaxies are moving away from us Now, his diagram is used to calculate the distance to faraway galaxies that do NOT have Cepheids or Type 1a Supernovae in them H0 - the Hubble constant was calculated from this graph H0 = v/d H0 = Hubble's constant v= velocity d= distance

Hubble’s Constant The Hubble Constant (slope) describes how fast objects appear to be moving away from our galaxy as a function of distance Distant galaxies are ALL redshifted…meaning they are receding from us From all of the previous methods, we figured out how far away tens of thousands of individual galaxies are Things farther from us are going away faster (more redshifted) than things closer to us (less redshifted)

Hubble’s constant We’ve plotted this relationship between amount of redshift and distance out onto a graph When we find a new galaxy, we measure the redshift from its spectrum, and use the graph to determine its distance from us Not super accurate, still some debate over the constant’s actual value Hubble was way wrong, thought it had a value around 500! He had the right idea though

The community is divided into two schools of thought; There is currently a strong debate on the value of the Hubble's constant fueled by new data from HST Cepheid studies of nearby galaxies. The community is divided into two schools of thought; 1) the old school which proposes a value for Hubble's constant around ~50 [(km/s)/Mps] to agree with the ages of the oldest stars in our Galaxy, and 2) a newer, and larger school which finds a higher Hubble's constant of ~67-75. This higher value poses a problem for modern cosmology in that the age of the Universe from Hubble's constant is less than the age of the oldest stars as determined by nuclear physics. (rate of fusion)

So the dilemma is this, either something is wrong with nuclear physics or something is wrong with our understanding of the geometry of the Universe.

It is important to figure out though because it helps us determine things like: The age of the universe The size of the universe What will happen to the universe in the future

Cosmological Constant One possible solution is the introduction of Einstein’s cosmological constant, once rejected as unnecessary to cosmology, it has now grown in importance due to the conflict of stellar ages and the age of the Universe.

Cosmological Constant This is a mysterious force that can be interpreted as a repulsive force that exactly balances the pull of gravity if the universe was static It was the only way Einstein could get his equations to work when Hubble discovered the universe was expanding, Einstein took it back out of his equations because he didn’t need it. – he called it his BIGGEST BLUNDER

Everything is expanding away from everything else! Which means there is no center Everywhere seems to be the center at the same time

Question of the day How does Hubble's law help determine distances to the most remote galaxies?

Checking In Questions… If a galaxy’s spectral lines are redshifted by 3%, how fast is the galaxy moving away from us?

Checking In Questions… If a galaxy’s spectral lines are redshifted by 3%, how fast is the galaxy moving away from us? 3% the speed of light = 0.03(3x108m/s) = 9x106m/s

Checking In Questions… If a galaxy’s spectral lines are redshifted by 3%, how fast is the galaxy moving away from us? 3% the speed of light = 0.03(3x108m/s) = 9x106m/s 2. Spectral lines shifted 318-300 and 339.2-320 observed-rest/rest = 318-300/300 = 0.06 observed-rest/rest = 339.2-320/320=0.06 0.06(3x108m/s) = 1.8x107m/s 1,800,000 m/s

Checking In Redshift = .002 0.002(3x108m/s) = 6X105m/s = 6x102km/s Hubble Constant = 25km/s per million light years Velocity = 6x102km/s d= v/H0 d= (6x102km/s) / (25km/s per million light years) d= (6x102km/s) / (25km/s)/(106ly) d=(6x102km/s) x (106ly)/(25km/s) d=(6x102)x (106ly)/(25) d=2.4x107 light years

This is due at Midnight It is on Google Classroom