Astronomy 1010- Ch. 1
What determines the chemistry of the universe?
-The chemistry of the universe is mostly hydrogen and helium (with a little lithium). We and Earth are made of other things like carbon, nitrogen, oxygen, and iron. This chemistry of the universe was manufactured by stars through nuclear fusion (makes stars shine) and through nuclear reactions (the explosions that end stellar lives). -Our solar system was formed by the earlier generation of stars convering 2% of our galaxy's hydrogen and helium into heavier elements. The cloud gave birth to our solar system and the 2% of other elements are what is responsible for the planets. This 2% accounts for life on Earth today. -So basically, most of us and our planet was created inside stars that lived and died before the birth of our Sun. That's why "we are star stuff." -Carl Sagan
Describe this picture. What does it tell us about the Universe?
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How can you use the angular size of an object to tell its distance?
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How can you use the apparent brightness of an object to tell its distance?
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What does chemical change have to do with the abundance of life in the Universe? Is timing important?
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What do we mean by a geocentric universe? In broad terms contrast a geocentric view of the universe with our modern view of the universe. Briefly describe the major levels of structure (such as planet, star, galaxy) in the universe.
A geocentric universe is one in which Earth is the center of everything. In a modern view, we know that Earth is orbiting an actually average star in the vast, complex universe. Major levels of structure: planets, moon, asteroids and comets, the Sun= solar system, The Sun and all stars we can see make up the Milky-Way Galaxy (galaxy= a great island of stars in space, containing a few hundred million to a trillion or more stars), etc.
How would the Universe be different if it were 1 billion years old? If it were, 100 billion years old?
According to the cosmic calendar, in which the entirety of 14 billion years is made into a 12-month calendar, if the universe were only 1 billion years old, it would be much, much smaller than it is now because the Milky Way Galaxy would just be forming. (No sign of Earth anywhere near either). If it were 100 billion years old, the universe would still be expanding and would be much, much larger than it is now at only 14 billion years old.
Where are we in the Universe?
Earth is a planet in the Solar System, which is a part of the Milky Way Galaxy, which is a part of the Local Group, which is a part of the Local Supercluster, which is part of the Universe. Basically, the Universe that we are in is the sum total of all matter and energy-encompassing the superclusters and voids and everything within them.
Are there variations in chemical composition from place to place in the Universe? If so, what causes them? [Think small scale and then large scale.]
Of course, small scale, the planets in our solar system are composed of different elements. And large scale, our galaxy as 2% of itself that includes elements other than hydrogen and helium, while some galaxies do not have any of these elements present. Past that, our universe is mostly made up of hydrogen and helium (and a little lithium).
What is the shape of the Milky Way Galaxy? Where is our solar system located within the galaxy? How does our solar system move within the galaxy?
On a scale of 1 to 1019, the Milky Way Galaxy is the size of 100m (a football field). Our entire solar system is a microscopic dot located around the 20-yard line. Our solar system moves first within our local solar neighborhood (the region of the Sun and nearby stars). Stars within this move at random and quite fast. Past that, the Milky Way Galaxy (on a grand scale) is essentially rotating. Our solar system completes one orbit of the galaxy in about 230 million years (unnoticeable).
What did Carl Sagan mean when he said that we are "star stuff "?
Our solar system was formed by the earlier generation of stars convering 2% of our galaxy's hydrogen and helium into heavier elements. The cloud gave birth to our solar system and the 2% of other elements are what is responsible for the planets. This 2% accounts for life on Earth today. -So basically, most of us and our planet was created inside stars that lived and died before the birth of our Sun. That's why "we are star stuff." -Carl Sagan
Distinguish between our galaxy's disk and halo. Where do most visible stars reside? Where does the mysterious dark matter seem to reside?
The Milky Way Galaxy's disk is the outside edge of our galaxy. The Halo is the spherical halo surrounding the entire disk. Most visible stars reside in the disk, but most of the mass of the Galaxy lies in the halo. Since we don't know the nature of this mass, we call it "dark matter" (in the halo).
What do we mean by the observable universe? Is it the same thing as the entire universe?
The distance of 14 billion light-years makes the boundary of our observable universe. Basically, this is how far away we can see the light from things in space. No, it is NOT the same things as the entire universe because we have no way of knowing what is beyond the bounds of our observable universe.
Explain the statement 'The farther away we look in distance, the further back we look in time.'
The statement (the farther away we look in distance, the further back we look in time) is true because light takes time to travel through space. Light travels insanely fast (300,000 km/s), but since things in space are extremely far away from us, it takes a long time for light from certain objects to reach us. So if we are looking at an object that is very far away, we are seeing what it looked like long ago (depending on how many light-years it is away). -Ex. Sirius (the Northern star[the brightest in the night sky]) is about 8 light-years away, meaning it takes 8 years for its light to reach us, therefore we see Sirius as it was 8 years ago. -Ex. LONG example. Andromeda Galaxy (M31) is about 2.5 million light-years from Earth, therefore we see it as it was 2.5 million years ago because that is how long it takes its light to reach us here on Earth.
What key observations by Edwin Hubble lead us to conclude that the universe is expanding? Use the raisin cake model to explain how these observations imply expansion.
The two key observations are that: a. Virtually every galaxy outside the Local Group is moving away from us. And b. The more distant the galaxy, the faster it appears to be racing away. -Meaning? The entire universe is expanding -Ex. Imagine a raisin cake in which adjacent raisins are 1 cm apart. While baking, after 1 hr, the raisins are 3 cm apart. If we were one of those raisins, we would see a nearby raisin (1 cm away) move 2 cm. away during baking. But a raising starting 2 cm away would be 4 cm away (so its speed is twice that of the 1st raisin). -Like the expanding dough of the cake, space itself is growing between galaxies. -HOWEVER, our universe has no center and no edges.
What do we mean when we say that the universe is expanding? How does expansion lead to the idea of the Big Bang?
The universe is expanding, meaning that average distance between galaxies are increasing with time- implying that galaxies must have been closer together in the past. Therefore, if we go back far enough, we'd reach the point where expansion began. AKA the Big Bang (about 14 billion years ago).
How old is the universe? How can we tell?
The universe is roughly 14 billion years old. We know this because of the portion of the universe that we can see (in principle). When we look at things in space, we are seeing them as they were in the past. If we tried to look at things more than 14-billion light years away, we would see nothing because the universe did not exist then.
How are we moving in the universe?
We are never sitting still. We spin around Earth's axis, which orbits the Sun. Our solar system moves among stars of the local solar neighborhood, while also orbiting the center of the Milky Way Galaxy. Our galaxy moves among other galaxies of the Local Group, and all of those galaxies move away from us.
