5) Section 1.3 and Figure 1.16 describe the Raisin Cake analogy for understanding why a uniform expansion of the universe appears as if all galaxies are moving away and more distant galaxies are moving faster. Consider Raisin #2 away from the “Local Raisin", which had a distance before baking of 3 cm and after baking of 9 cm. Let's say you accidentally forget to turn the oven off and the cake expands by another factor of 9 after another two hours. How far away is Raisin #2 now? Comparing the rough average speed during the first hour and the rough average speed during the second hour, did its speed seem to increase, decrease, or stay the same?

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Would the raisin be 81 cm away if it’s expanding by a factor of 9? I don’t understand how to find the speed during the first hour and the second hour.
O convert 2.61*10^22 km to ly-
2module_item_id%3D9926549
1.pdf
1 F2021.pdf
HW1_F2021.pdf (142 KB)
4) The cosmic calendar of Section 1.2 explains where we are in the universe in time. But time
and space are connected through the speed of light. How far could light travel in 1 week of the
"cosmic calendar" in light-years? What astronomical object in Figure 1.1 is approximately this
size?
5) Section 1.3 and Figure 1.16 describe the Raisin Cake analogy for understanding why a
uniform expansion of the universe appears as if all galaxies are moving away and more distant
galaxies are moving faster. Consider Raisin #2 away from the “Local Raisin", which had a
distance before baking of 3 cm and after baking of 9 cm. Let's say you accidentally forget to turn
the oven off and the cake expands by another factor of 9 after another two hours. How far away
is Raisin #2 now? Comparing the rough average speed during the first hour and the rough
average speed during the second hour, did its speed seem to increase, decrease, or stay the same?
6) In Section 1.4 the authors state that astronomy and technology develop hand-in-hand. Verify
this by identifying one example of astronomy software. You can list an app or you can find a
computer software that looks interesting to you. (No need to actually installing anything but you
obviously can if you want to)
7) The Moon used to be much closer to the Earth. What distance away would the Moon have to
be to have an angular size of about 5 degrees? What is a similar size based on Figure 2.7c?
021
Transcribed Image Text:O convert 2.61*10^22 km to ly- 2module_item_id%3D9926549 1.pdf 1 F2021.pdf HW1_F2021.pdf (142 KB) 4) The cosmic calendar of Section 1.2 explains where we are in the universe in time. But time and space are connected through the speed of light. How far could light travel in 1 week of the "cosmic calendar" in light-years? What astronomical object in Figure 1.1 is approximately this size? 5) Section 1.3 and Figure 1.16 describe the Raisin Cake analogy for understanding why a uniform expansion of the universe appears as if all galaxies are moving away and more distant galaxies are moving faster. Consider Raisin #2 away from the “Local Raisin", which had a distance before baking of 3 cm and after baking of 9 cm. Let's say you accidentally forget to turn the oven off and the cake expands by another factor of 9 after another two hours. How far away is Raisin #2 now? Comparing the rough average speed during the first hour and the rough average speed during the second hour, did its speed seem to increase, decrease, or stay the same? 6) In Section 1.4 the authors state that astronomy and technology develop hand-in-hand. Verify this by identifying one example of astronomy software. You can list an app or you can find a computer software that looks interesting to you. (No need to actually installing anything but you obviously can if you want to) 7) The Moon used to be much closer to the Earth. What distance away would the Moon have to be to have an angular size of about 5 degrees? What is a similar size based on Figure 2.7c? 021
us faster because they are cana cake. You can also now
be noticeable on the time scale of a human life. Instead,
the Local Raisin. Notice, for example, that Raisin 1 starts
of the universe. Like the expanding
More distant galaxies move away Irom
the expanding universe. Someone living in one of th isins inside
all other raisins are moving away, with more distant : ns moving
away faster. In the same way, we know that we live ir er expanding
universe because all galaxies outside our Local Gro.e moving
a raisin cake, we can't actually see galaxies moving apan
It's also important to realize that, unlike the case with
basic
pie
is
away
this
Sin cake in which the distance between adjacent raisins
edistant
ing between galaxies.
beca
dough between
expansion
carried along with
Iit expands as it bakes. After 1 hour, you remove the can
like the raisins in the
m uhe
of
allow us to measure the
how observations
of the universe:
expansion of the cake seems fairly obvious. But what would
auo The faster the rate of expansion, th
" the Local Raisin. Figure 1.17 shows one possible choice,
with three nearby raisins also labeled, The accompanying
out at a distance of 1 centimeter before baking and ends uP
at a distance of 3 centimeters after baking, which means
it moves a distance of 2 centimeters farther away from une
Local Raisin during the hour of baking, Hence, its speed as
seen from the Local Raisin is 2
moves from a distance of 2 centimeters before baking to
distance of 6 centimeters after baking, which means it
hour. Raisin
2 centimeters per
moves
distance of 4 centimeters farther away from the
Local Raisin during the hour. Hence, its speed is 4 centime-
ters per hour, or twice the speed of Raisin 1. Generalizing,
the fact that the cake is expanding means that all the raisins
are moving away from the Local Raisin, with more distant
raisins moving away faster.
Can
with time-the distances are too Vast for any motion
we measure the speeds of galaxies by spreading their lieh
into spectra and observing what we call Doppler shit
[Section 5.4). This illustrates how modern astrono
depends both on careful observations and on using qur
understanding of the laws of nature to explain what we se
Think about It Suppose a raisin started out 10 centimeters
from the Local Raisin. How far away would it be after 1 hour,
and how fast would it be moving away from the Local Raisin?
Hubble's discovery that galaxies are moving in much the
same way as the raisins in the cake, with most moving away
from us and more distant ones moving away faster, implies
that the universe is expanding much like the raisin cake. If
Motion Summary FIGURE 1.18 summarizes the motions e
have discussed. As we have seen, we are never truly sitting
still. We spin around Earth's axis at more than 1000 kilome
ters per hour, while our planet orbits the Sun at more than
100,000 kilometers per hour. Our solar system moves among
the stars of the local solar neighborhood at a typical speed of
70,000 kilometers per hour, while also orbiting the center of
the Milky Way Galaxy at a speed of about 800,000 kilometers
per hour. Our galaxy moves among the other galaxies of the
1
1 cm
1 cm
cm
Before baking: raisins
/are all 1 cm apart.
Local Raisin
From an outside
perspective, the cake
expands uniformly as
it bakes...
1
hr
Distances and Speeds as Seen from the Local Raisin
After baking:
raisins are all
3 cm apart
Distance
Before
Baking
Distance
After Baking
(1 hour later) Speed
Raisin
3 ст
3 cm
Number
Local
Raisin
1
1 cm
3 cm
2
2 cm/hr
2 cm
6 cm
3
4 cm/hr
3 cm
9 cm
6 cm/hr
FIGURE 1.17 An expanding raisin cake offers
...but from the point of view of the Local Raisin
all other raisins move farther away during baking
with more distant raisins moving faster.
the cake could figure out that the cake is expanding
nalogy to
noticing that
PART I DEVELOPING PERSPECTIVE
away from us, with more distant ones moving faster
18
Transcribed Image Text:us faster because they are cana cake. You can also now be noticeable on the time scale of a human life. Instead, the Local Raisin. Notice, for example, that Raisin 1 starts of the universe. Like the expanding More distant galaxies move away Irom the expanding universe. Someone living in one of th isins inside all other raisins are moving away, with more distant : ns moving away faster. In the same way, we know that we live ir er expanding universe because all galaxies outside our Local Gro.e moving a raisin cake, we can't actually see galaxies moving apan It's also important to realize that, unlike the case with basic pie is away this Sin cake in which the distance between adjacent raisins edistant ing between galaxies. beca dough between expansion carried along with Iit expands as it bakes. After 1 hour, you remove the can like the raisins in the m uhe of allow us to measure the how observations of the universe: expansion of the cake seems fairly obvious. But what would auo The faster the rate of expansion, th " the Local Raisin. Figure 1.17 shows one possible choice, with three nearby raisins also labeled, The accompanying out at a distance of 1 centimeter before baking and ends uP at a distance of 3 centimeters after baking, which means it moves a distance of 2 centimeters farther away from une Local Raisin during the hour of baking, Hence, its speed as seen from the Local Raisin is 2 moves from a distance of 2 centimeters before baking to distance of 6 centimeters after baking, which means it hour. Raisin 2 centimeters per moves distance of 4 centimeters farther away from the Local Raisin during the hour. Hence, its speed is 4 centime- ters per hour, or twice the speed of Raisin 1. Generalizing, the fact that the cake is expanding means that all the raisins are moving away from the Local Raisin, with more distant raisins moving away faster. Can with time-the distances are too Vast for any motion we measure the speeds of galaxies by spreading their lieh into spectra and observing what we call Doppler shit [Section 5.4). This illustrates how modern astrono depends both on careful observations and on using qur understanding of the laws of nature to explain what we se Think about It Suppose a raisin started out 10 centimeters from the Local Raisin. How far away would it be after 1 hour, and how fast would it be moving away from the Local Raisin? Hubble's discovery that galaxies are moving in much the same way as the raisins in the cake, with most moving away from us and more distant ones moving away faster, implies that the universe is expanding much like the raisin cake. If Motion Summary FIGURE 1.18 summarizes the motions e have discussed. As we have seen, we are never truly sitting still. We spin around Earth's axis at more than 1000 kilome ters per hour, while our planet orbits the Sun at more than 100,000 kilometers per hour. Our solar system moves among the stars of the local solar neighborhood at a typical speed of 70,000 kilometers per hour, while also orbiting the center of the Milky Way Galaxy at a speed of about 800,000 kilometers per hour. Our galaxy moves among the other galaxies of the 1 1 cm 1 cm cm Before baking: raisins /are all 1 cm apart. Local Raisin From an outside perspective, the cake expands uniformly as it bakes... 1 hr Distances and Speeds as Seen from the Local Raisin After baking: raisins are all 3 cm apart Distance Before Baking Distance After Baking (1 hour later) Speed Raisin 3 ст 3 cm Number Local Raisin 1 1 cm 3 cm 2 2 cm/hr 2 cm 6 cm 3 4 cm/hr 3 cm 9 cm 6 cm/hr FIGURE 1.17 An expanding raisin cake offers ...but from the point of view of the Local Raisin all other raisins move farther away during baking with more distant raisins moving faster. the cake could figure out that the cake is expanding nalogy to noticing that PART I DEVELOPING PERSPECTIVE away from us, with more distant ones moving faster 18
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