![]() ![]() In short scales, the expansion of the universe does not have any effect on gravitational bounded structures. By large scale, we mean distances more than 100. In fact, the expansion of the universe applies only on large scales. The method used by Hubble was correct, but the number he calculated for was NOT correct. It means that if a galaxy is at 1 away from us, it is moving away from us at speed of 454. Note that the unit of distance is and the unit of radial velocity is. Let’s first plot the dataset points and the regression line and then explain it.Īx.plot(x, slope*x + intercept, color='red')Īx.set_ylabel('Recessional Velocity (km/s)') > slope, intercept = np.polyfit(x, y, 1)Īs you see slope is about 454. The polyfit function from numpy do this for us: ![]() We are going to find the slope of the line, which is. Let’s load the dataset and see a few rows of it.įor not being confused, let’s use x for representing distance and y for representing radial velocity. You can find the sample used by Hubble as a CSV file here. Now I’m going to do exactly what Hubble did in his famous article. We know that, so knowing the redshift of a galaxy, we can find its radial velocity simply by multiplying redshift by speed of light. Instead of radial velocity, he used redshift. Hubble used a sample of galaxies whose distances where known. In other words, the farther a galaxy is from us, the faster it is moving away from us. It states that galaxies are moving away from each other at a speed proportional to their distances. In this formula, is the radial velocity, is proper distance and is Hubble constant. This relation, which is known as Hubble’s Law, is represented as follow: In this article, Hubble presented a linear relationship between distance and radial velocities of a number of galaxies. He went to Mount Wilson Observatory to thank Hubble for his great discovery. After publishing Hubble’s article, Einstein called the assumption of static universe his biggest mistake. At that time, most of the scientists believed in a static universe. In 1929 Edwin Hubble published an article in which he presented empirical evidence that our universe is expanding.
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