### What Does Hubble’S Law Tell Us Quizlet?

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• 16 What does Hubble’s law tell us? The more distant a galaxy, the faster it is moving away from us.

## What does Hubble’s law tell us?

Interpreting these diagrams – On the y-axis, you plot the velocity of the galaxy obtained from the spectrum. On the x-axis, you plot the distance to that galaxy, in this case obtained from Cepheids. If these two quantities (distance and velocity) had nothing to do with each other, then the diagram would look like what we call a “scatter plot.” That is, it would appear as a bunch of points randomly placed in different locations.

• However, it is somewhat apparent in this case that you can draw a straight line through the points.
• What this means is that as the distance gets bigger, so does the velocity.
• In algebra class, you learned that the equation for a line that passes through the point (0,0) is: y = m x where y = the quantity plotted on the y-axis (velocity), x = the quantity plotted on the x-axis (distance), and m is the slope of the line.

For the specific case of this relationship, we usually write the equation this way: v = H 0 d H 0 is called the Hubble constant, It is the slope of the line that relates the distance of a galaxy to its velocity. If you know H 0 and if you can calculate the velocity, v, from the spectrum, then you can use this equation to calculate the distance, d, to that galaxy.

1. Let’s quickly review how we measure velocities for objects that are receding from us.
2. The equation that you saw in Lesson 4 for the Doppler shift was: Δ λ / λ 0 = v r / c Where Δλ is the difference between the measured wavelength for a line in the spectrum of an object and the wavelength for that same line observed in the spectrum of an object at rest.

The other term on the left hand side, λ 0, is the wavelength of that line in the spectrum of an object at rest. For objects at large distances from Earth where the distance is determined using Hubble’s Law, we do not often refer to their recession velocities (e.g., “that galaxy has a velocity of 14,000 km/sec away from us”) or their distances in Mpc (e.g., “that galaxy is 247 Mpc from us”), instead, we simply refer to the object’s redshift, z,

The definition of z is that it is the left hand side of the Doppler shift equation: z = Δ λ / λ 0 For example, if you observe a galaxy with an H-alpha line at 680 nm, and you know the rest wavelength for that line is 656.3 nm, then its redshift is: z = ( 680 n m − 656.3 n m ) / 656.3 n m = 0.036 Hubble’s law, which says simply that a galaxy’s velocity (or as is sometimes plotted, its redshift) is directly proportional to its distance, also tells us something important about the state of the universe.

If the universe is static and unchanging, there should be no correlation between distance and velocity. However, if the universe is expanding, we expect a correlation between distance and velocity. The usual analogy used here is that of an explosion – the fragments of shrapnel produced are moving with a range of velocities, and the most distant objects from the source of the explosion have the largest velocities.

1. Hubble’s Law only works for distant galaxies. For nearby galaxies (in the Local Group), stars inside the Milky Way, and for objects in our Solar System, the relationship between distance and velocity does not hold. The reason for the discrepancy for nearby galaxies is the “peculiar velocity” of the galaxy, that is, its real velocity through space that is unrelated to the expansion. For distant galaxies, their peculiar velocities are small enough that they still lie on or near the line for Hubble’s Law. For nearby galaxies, though, their peculiar velocity is larger than their velocity from the expansion, so their peculiar velocity dominates their total velocity, causing them to lie far from the line relating velocity to distance. For example, the galaxy M31 does not even show a redshift; it is blueshifted, showing that its peculiar velocity is pointed towards us, rather than away from us.
2. Recall the concept of the “lookback time” for an object. For objects at very large distances from us, it is very common to see their distances referred to not in units like parsecs or light years, but in units of time. For example, astronomers will say, “The light from this galaxy was emitted when the universe was 10% of its present age, over 12 billion years ago.” We base these descriptions on the redshift of the galaxy and the lookback time.

You can consider Hubble’s Law to be the final rung in the distance ladder. If you know Hubble’s constant accurately, then you can calculate the distance to any galaxy in the Universe simply by measuring its velocity (which is reasonably easy to do for any galaxy for which you can observe its spectrum).

To calibrate Hubble’s constant, though, you need to be able to plot the distances for a number of galaxies as obtained using other methods. While that may seem like an easy statement to make, it was an incredibly difficult task to accomplish. For decades, astronomers have argued over the precise value of Hubble’s constant.

This measurement was, in fact, one of the major reasons for building and launching the Hubble Space Telescope. It spent years observing Cepheid variables in distant galaxies in order to measure Hubble’s constant as precisely as possible. The results were reported in 1999.

## What do Hubble’s observations tell us about the universe?

Hubble finds proof that the universe is expanding 1929 The two keys to Edwin Hubble ‘s breakthrough discovery were forged by others in the 1910s. The first key, the period-luminosity scale discovered by Henrietta Leavitt, allowed astronomers to calculate the distance to variable stars from Earth.

Hubble had already used this knowledge in his 1924 discovery that the Andromeda nebula, containing a variable star, was more than 900,000 light years from Earth – way beyond our own galaxy – a surprise to everyone at the time. With this scale and other tools, Hubble had found and measured 23 other galaxies out to a distance of about 20 million light years.

The second key was the work of Vesto Slipher, who had investigated the spiral nebulae, before Hubble’s Andromeda discovery. These bodies emit light which can be split into its component colors on a spectrum. Lines then appear in this spectrum in particular patterns depending on the elements in the light source.

• Yet if the light source is moving away, the lines are shifted into the red part of the spectrum.
• Analyzing the light from the nebulae, Slipher found that nearly all of them appeared to be moving away from Earth.
• Slipher knew that a shift toward red suggested the body was moving rapidly away from the observer.

But he had no way to measure the distances to these reddish bodies. Hubble’s brilliant observation was that the red shift of galaxies was directly proportional to the distance of the galaxy from earth. That meant that things farther away from Earth were moving away faster.

1. In other words, the universe must be expanding.
2. He announced his finding in 1929.
3. The ratio of distance to redshift was 170 kilometers/second per light year of distance, now called Hubble’s constant.
4. The numbers were not exactly right, and refinements in measuring techniques and technology have changed all of Hubble’s early figures.

But not the basic principle. He himself kept working on the problem and collecting data throughout his career. Some view Hubble’s discovery as the most important event in astronomy in the century. It made the most basic change in our view of the world since Copernicus 400 years ago.

## How does Hubble’s Law tell us the age of the universe?

Print If we agree that Hubble’s Law tells us that the universe is expanding, it also implies that in the past the universe was much smaller than it is today. If we assume that the expansion’s apparent velocity (that is, how fast the galaxies appear to be moving apart) has been constant over the history of the universe, we can calculate how long ago the galaxies began their separation.

This should tell us the time that the expansion began, which should give us an estimate of the age of the universe. If the expansion of the universe is happening rapidly, then we expect the universe to be relatively young, because it has taken only a short time for the galaxies to expand to large distances.

If, on the other hand, the universal expansion is progressing at a slow speed, then the age of the universe should be relatively old, because it has taken a long time for the galaxies to reach large distances from each other. We know how fast the universe is expanding, because we know the value of Hubble’s constant (H 0 ).

The faster the universe is expanding, the faster the galaxies will appear to be moving away from each other. You can actually calculate an estimate for the age of the Universe from Hubble’s Law. The distance between two galaxies is D. The apparent velocity with which they are separating from each other is v.

At some point, the galaxies were touching, and we can consider that time the moment of the Big Bang. If you take the separation between the two galaxies (D) and divide that by the apparent velocity (v), that will leave you with how long it took for the galaxies to reach their current separation.

So, the time it has taken for the galaxies to reach their current separations is t = D / v, But, from Hubble’s Law, we know that v = H 0 D, So, t = D / v = D / ( H 0 × D ) = 1 / H 0, So, you can take 1 / H 0 as an estimate for the age of the Universe. The best estimate for H 0 = 73 k m / s / M p c, To turn this into an age, we’ll have to do a unit conversion. Since 1 M p c = 3.08 × 10 19 k m, H 0 = ( 73 k m / s / M p c ) x ( 1 M p c / 3.08 x 10 19 k m ) = 2.37 x 10 − 18 1 / s, So, the age of the Universe is t = 1 / H 0 = 1 / 2.37 x 10 − 18 1 / s = 4.22 x 10 17 s = 13.4 b i l l i o n y e a r s,

From stellar evolution, we have estimated the ages of the oldest globular clusters to be approximately 12-13 billion years old. These are the oldest objects we have identified, and it is a nice check on our estimates for the age of the Universe that they are consistent.

It would have been strange if we were unable to find any objects roughly as old as the Universe or if we found anything significantly older than the estimated age of the Universe. For many years, until about 10 years ago, however, there was a controversy over the age of the universe derived from Hubble’s Constant.

The best theories available at the time were estimating that the stars at the Main Sequence Turn Off in many globular clusters had ages of 15 billion years old or more. This creates a problem. How can the universe contain an object older than itself? Recently, however, advances in our understanding of the stars have led us to refine the ages of the stars in globular clusters, and we now estimate them to be about 13 billion years old.

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## What Hubble’s law is and how it’s evidence for the origin of our universe?

Hubble’s Law basically states that the greater the distance of a galaxy from ours, the faster it recedes. It was proof that the Universe is expanding. It was also the first observational support for a new theory on the origin of the Universe proposed by Georges Lemaitre: the Big Bang.

#### Why is Hubble’s law so important?

Learn more about breakthroughs pioneered at the University of Chicago The Hubble constant is one of the most important numbers in cosmology because it tells us how fast the universe is expanding, which can be used to determine the age of the universe and its history. It gets its name from UChicago alum Edwin Hubble, who was first to calculate the constant from his measurements of stars in 1929.

#### What does Hubble’s law tell us about the size of the universe?

It indicates a constant expansion of the cosmos where, like in an expanding raisin cake that swells in size, galaxies, like the raisins, recede from each other at a constant speed per unit distance; thus, more distant objects move faster than nearby ones.

### Why did Hubble’s data change our view of the universe?

How Space Detective Edwin Hubble Changed Our View of the Universe You might know him from the powerful space-based telescope that bears his name, but did you know that Edwin P. Hubble radically changed our view of the universe? Using deduction and measurements of starlight, Hubble acted as a cosmic detective to prove that our universe is not static but is in fact constantly growing.

1. Astronomers used to think that our universe was made up only of the Milky Way, and that everything in space was stationary.
2. Distant galaxies were once thought to be gas clouds in the Milky Way.
3. In 1925, Hubble proved that the universe is much larger than was believed.
4. He created a method of measurement based on the discovery of another astronomer, Henrietta Leavitt.

In 1912, she had observed that a type of star called a Cepheid variable had a measurable pulsation rate and luminosity, or brightness. Hubble found that by timing a star’s fluctuations of luminosity, he could measure its distance from Earth. With this technique, Hubble proved that the nearby Andromeda nebula was not a gas cloud in our own galaxy, but was actually a separate galaxy.

• His announcement literally changed how we see the universe.
• But his detective work didn’t stop there.
• He continued to measure the distances of objects in outer space and collected enough data to prove a linear relationship between their distance and speed.
• This came to be known as Hubble’s Law.
• It proved that the universe is expanding.

It’s also the cornerstone of the Big Bang Theory, the most widely accepted explanation of the origin of our universe. Despite the huge implications of his discovery, Hubble could not be nominated for the Nobel Prize in Physics, because astronomy was not recognized by the Nobel Prize committee.

### What Hubble’s law is and how it’s evidence for the origin of our universe?

Hubble’s Law basically states that the greater the distance of a galaxy from ours, the faster it recedes. It was proof that the Universe is expanding. It was also the first observational support for a new theory on the origin of the Universe proposed by Georges Lemaitre: the Big Bang.