Homework: Due at Midnight Google classroom

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?.

After Bellwork, Read the FYI on the “Cosmological Distance Ladder” then answer the two questions in your science journal

Question of the day How do we measure the distances to very distant objects in space?

Distance Ladder The Cosmic Distance Ladder -- is the way astronomers measure the distance of objects in space. No one method works for all objects and distances, so astronomers use a number of methods. Standard Candle -- a class of astrophysical objects, such as supernovae or variable stars, which have known luminosity due to some characteristic quality possessed by the entire class of objects. We are constantly Updating and refining these techniques as technology improves and knowledge increases

Info for foldable later…

The Most Common Techniques on the Cosmological Distance Ladder Radar Reflected pulses of energy sent from earth Parallax Observe motion against the background sky (works for stars up to 150ly away) Main Sequence Fitting Plot star clusters, shift to meet normal location of main sequence. Distance you have to shift is a function of distance Cepheid Variable Stars Period of brightness fluctuations is a function of absolute brightness, we can compare close Cepheids with distant Cepheids. Tully-Fisher Relation The larger a galaxy is, the faster it spins; meaning if we can measure its spin, we can determine its size. From it’s size we can determine its absolute luminosity, and from that value, we can determine its distance Type 1a Supernovae Mass limit of explosion of a white dwarf is the same, so the peak brightness is the same. We can compare the apparent brightness we see with the absolute brightness to calculate distance. Hubble’s Law Objects observed in deep space are found to have a Doppler shift caused by its relative velocity away from us; This Doppler-shift-measured velocity, of various galaxies receding from the Earth, is approximately proportional to their distance from the Earth for galaxies up to a few hundred mega parsecs away

The Virgo Cluster: 16.5 ± 0.1 Mpc (53.8 ± 0.3 Mly)

Radar Ranging radar ranging, where a radio pulse is reflected off of the various planets in the Solar System. Most Accurate. Relies on our knowledge of the speed of light. Only useful within the solar system

Parallax How things appear to change in the night sky based on our position Only good to about 150 light years away BUT…. There are hundreds of stars within this distance Pretty accurate Becomes a calibrator for other distance indicators

Main Sequence Fitting If you find a stars spectrum you can determine a lot of info like whether it is a main sequence star as well as it’s temperature This means you can determine what the luminosity should be If you measure a stars luminosity and it is different than what it should be, it is because of distance, so you adjust it Based on how much you adjust it, tells you how far away it is

Cepheid Variables These stars change in luminosity over short periods There is a relationship between the period of oscillation and the absolute brightness of the star This is the technique Edwin Hubble used Brighter stars have a longer period of oscillation First you measure the luminosity period

Tully-Fisher relation Spiral Galaxies rotate The larger the galaxy, the faster it spins We use Hydrogen spectrum lines to measure its spin rate (Doppler effect) When we know the spin, we calculate it’s size from the graph below When we know its size, we can calculate its luminosity based on how many stars there should be

White Dwarf Supernovae (type 1a) Because these always happen when the white dwarf reaches 1.4 solar masses, they ALWAYS release the same amount of energy 1–2×1044 J This knowledge allows us to compare the apparent magnitude with its absolute magnitude (Mv = −19.3 or about 5 billion times brighter than the Sun), with little variation, and then calculate a distance Very helpful, because we can see these from across the universe!!

Question of the day How do we measure the distances to very distant objects in space?

Instructions on mrhyatt Instructions on mrhyatt.rocks Due Tomorrow DON’T just copy all of my pictures