Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional)...
Transcript of Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional)...
![Page 1: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/1.jpg)
15.2 Distances of Galaxies
• Our Goals for Learning• How do we measure the distances to galaxies?
• What is Hubble’s Law?
• How do distance measurements tell us the age of the universe?
![Page 2: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/2.jpg)
How do we measure the distances to galaxies?
![Page 3: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/3.jpg)
Step 1
Determine size of solar system using radar
![Page 4: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/4.jpg)
Step 2
Determine distances of stars out to a few hundred lightyears using parallax
![Page 5: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/5.jpg)
Brightness alone does not provide enough information to measure distance
![Page 6: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/6.jpg)
The relationship between apparent brightness and luminosity depends on distance:
Luminosity Brightness = 4 pi x (distance)2
We can determine a star’s distance if we know its luminosity and can measure its apparent brightness:
Luminosity Distance = 4 pi x Brightness
A standard candle is an object whose luminosity we can determine without measuring its distance.We can use standard candles to measure distances.
![Page 7: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/7.jpg)
Step 3
Apparent brightness of star cluster’s main sequence tells us its distance
![Page 8: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/8.jpg)
Which kind of stars are best for measuring large distances?
10%
8%
82%
:00
1. Highluminosity stars
2. Mediumluminosity stars
3. Lowluminosity stars
![Page 9: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/9.jpg)
Cepheid variable stars are very luminous
![Page 10: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/10.jpg)
Cepheid variable stars with longer periods have greater luminosities
![Page 11: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/11.jpg)
Step 4
The period of a Cepheid variable star tells us its luminosity. Its luminosity plus its apparent brightness tells us its distance.
So we can use Cepheid variable stars as standard candles to measure distances.
![Page 12: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/12.jpg)
Edwin Hubble, using Cepheids as standard candles, was the first to measure distances to other galaxies
![Page 13: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/13.jpg)
Measuring distances using Cepheids has been a key mission of the Hubble Space Telescope
![Page 14: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/14.jpg)
Hubble’s extrasharp vision allows us to observe individual Cepheid variable stars in galaxies up to 100 million lightyears away
Galaxy M100
![Page 15: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/15.jpg)
Clicker Question: You’ve found a Cepheid variable star in Galaxy A with a period of 100 days. You've also found a Cepheid variable star in Galaxy B with a period of 10 days. Both Cepheids have the same brightness as seen from Earth. Which galaxy is farther away from us?
• GET YOUR ANSWER READY:
• A) Galaxy A• B) Galaxy B• C) Both are the
same distance
![Page 16: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/16.jpg)
Which galaxy is farther away?
10%
9%
81%
:00
1. Galaxy A
2. Galaxy B
3. Both are the same distance
![Page 17: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/17.jpg)
Whitedwarf supernovae can also be used as standard candles
![Page 18: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/18.jpg)
Step 5
Apparent brightness of whitedwarf supernova (another kind of standard candle) tells us the distance to its galaxy
(up to 10 billion lightyears)
Supernova
![Page 19: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/19.jpg)
In summary, we measure galaxy distances using a chain of techniques known as the distance ladder
![Page 20: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/20.jpg)
What is Hubble’s Law?
![Page 21: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/21.jpg)
By measuring velocities and distances of galaxies, Hubble found that a galaxy’s velocity and distance are related in a special way
![Page 22: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/22.jpg)
The spectral features of virtually all galaxies are redshifted ⇒ They’re all moving away from us
![Page 23: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/23.jpg)
Hubble’s Law: velocity = H0 x distance
![Page 24: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/24.jpg)
Redshift of a galaxy tells us its distance through Hubble’s Law:
distance =
velocity H0
![Page 25: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/25.jpg)
Distances of farthest galaxies are measured from redshifts
![Page 26: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/26.jpg)
What have we learned?• How do we measure the distances to galaxies?• Our measurements of galaxy distances depend on a
chain of methods. The chain begins with radar ranging in our own solar system and parallax measurements of distances
![Page 27: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/27.jpg)
What have we learned?
• What is Hubble’s law?• Hubble’s law tells us
that more distant galaxies are moving away faster. It allows us to determine a galaxy’s distance from the speed at which it is moving away from us, which we can measure from its Doppler shift.
![Page 28: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/28.jpg)
Activity #49, page 185188
• Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times.
• Use it to answer the questions in Part I on page 185.• We’ll do those as clicker questions, then do the
same for Part II.
![Page 29: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/29.jpg)
2. If you were in one of the other galaxies, would the MW (Milky Way) galaxy appear
to be moving away from you?
Yes N
o
It de
pends
88%
3%9%
:00
1. Yes2. No3. It depends
![Page 30: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/30.jpg)
4. Are any of the galaxies moving closer to each other?
Yes N
o
May
be
16%
4%
80%
:00
1. Yes2. No3. Maybe
![Page 31: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/31.jpg)
5. If we measured radial velocities of other galaxies, what would we see?
All g
alaxie
s red
shift
ed
All g
alaxie
s blues
hifted
Some g
alaxie
s red
shi...
88%
10%2%
:00
1. All galaxies redshifted
2. All galaxies blueshifted
3. Some galaxies redshifted, some galaxies blueshifted
![Page 32: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/32.jpg)
6. If someone in another galaxy measured radial velocities of galaxies besides their
own, what would they see?
All o
ther
galax
ies re
d...
All o
ther
galax
ies blu...
Some g
alaxie
s red
shi...
84%
12%4%
:00
1. All other galaxies redshifted
2. All other galaxies blueshifted
3. Some galaxies redshifted, some galaxies blueshifted
![Page 33: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/33.jpg)
Part II, page 187 (instructions on page 186)
• Using Figure 2, fill in the blank entries in the lower right of Table 1: you’re measuring how far galaxies A and B moved between images II and III, divided by the time elapsed between images II and III.
• Then, using the bottom row of Table 1 (which you’ve just filled in), in Figure 3 plot the velocities of galaxies A and B as a function of their distance.
• Then answer questions 8D, 9, 10.
![Page 34: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/34.jpg)
8D. Figure 3 shows that the farther away a galaxy is, the ___ it is moving away from
the reference galaxy.
Faster
Slow
er
Neit
her –
spee
d is i
n...
88%
4%8%
:00
1. Faster2. Slower3. Neither – speed is
independent of distance
![Page 35: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/35.jpg)
9. How long has galaxy B been travelling if it started at the origin in Fig. 2, moved at constant speed, and ended up at its position in Image III?
6%
39%
55%
:00
1. 2 billion years
2. 4 billion years
3. 8 billion years
![Page 36: Our Goals for Learning - York University · • Page 186 has 3 photos of a flat (2dimensional) universe of galaxies, taken at 3 different times. • Use it to answer the questions](https://reader033.fdocuments.in/reader033/viewer/2022041608/5e3624e81d789a5b2215eb94/html5/thumbnails/36.jpg)
10. Who do you think is correct?
90%
10%
:00
1. Sam
2. Samantha