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Course: Big History Project > Unit 2
Lesson 4: Other MaterialsREAD: Gallery — How Did Our Understanding of the Universe Change?
Google ClassroomBrowse through different views of the Universe and zoom in on the light from distant stars to better understand how our understanding of cosmology has evolved.
Ptolemy's Universe
The Ptolemaic view of the Universe was an Earth-centered, or geocentric, model. The Sun and all of the planets orbited the Earth and the other stars formed a backdrop that also orbited Earth.
The Copernican Model
The idea of a Sun-centered, or heliocentric, view of the Universe had been suggested by ancient Greek astronomers like Aristarchos and was later published by Polish astronomer Nicolaus Copernicus in 1543. To some extent, this model (not at actual scale in this illustration) ushered in a new age of astronomy.
Kepler and Elliptical Orbits
The German astronomer and mathematician Johannes Kepler demonstrated that the orbits of Earth and the other planets (not drawn to scale in this illustration) were not perfectly circular but were actually elliptical, or egg-shaped.
Redshift
This illustration simulates the redshift, or Doppler shift, that affects how light waves appear to us when the source of light is moving away. When we view galaxies from Earth, their light is shifted to the red side of the color spectrum, an indication that they are moving away from us. This is strong evidence for an expanding Universe.
The Electromagnetic Spectrum
It's important to remember that what we see as visible light is only a small portion of the full electromagnetic spectrum. Many modern telescopes are able to view different wavelengths of electromagnetic energy, thus generating images from space that are completely invisible to the unaided eye.
Spectral Lines
The color of light from objects in space can be used for more than gauging distances. Different elements actually leave their own "signatures" in light. Scientists can use spectral lines to determine the chemical composition of objects in space like other stars and planets. Hydrogen, helium, and oxygen are the three most abundant elements in the Universe.
Cepheid Variable Star V1 in the Andromeda Galaxy
Astronomers use the fluctuating brightness of Cepheid variable stars like V1 as "stellar yardsticks" to measure distances. The discovery of Cepheids and the understanding of how to interpret their fluctuations of brightness helped prove that the Universe was a much larger place than first thought.
Cepheids in the Galaxy NGC 5584
This illustration shows the location of the many Cepheid variable stars found in the spiral galaxy NGC 5584. Different Cepheids have different "periods" related to the total energy they put out as they burn hydrogen and helium.
The Horn Antenna
The Horn reflector antenna at Bell Telephone Laboratories in Holmdel, New Jersey was built in 1959 and became famous when Arno Penzias and Robert Wilson used it to detect the Cosmic Microwave Background (CMB), the afterglow of the Big Bang. In 1989 The Horn was dedicated to the U.S. National Park Service as a National Historic Landmark.
The Cosmic Microwave Background
These details of the CMB were captured by NASA's Wilkinson Microwave Anistropy Probe (WMAP) at the very start of the 21st century. The color-enhanced WMAP imagery of the infant Universe shows the slight variations in temperature that correspond to the slight variations in density that helped seed the formation of the first galaxies.
Want to join the conversation?
If other galaxies as well as the stars and other matters and materials surrounding us in our own milky way galaxy are still all expanding away from us, doesn't that kill one popular theory that there are black holes at the center of galaxies that cause the galaxies to spin? Or does that mean we are getting sucked into the black hole faster than everything else (The earth is contracting farther inward to the center faster than other matter in the galaxy)?
Also, isn't it sort of odd that earth spins on its axis rotating around a star in a galaxy that spins but where the star itself doesn't really spin or rotate? The gasses and materials comprising the stars are spinning and have differing rotations at their equators than at their poles ? Or maybe I'm not understanding the rotation of stars correctly...?(8 votes)
Regarding the black-hole question:
-Like cathddu said, the expansion of the universe doesn't happen within individual galaxies, because gravity holds a galaxy together and prevents space from expanding on these "small" scales. So expansion doesn't have anything to do with why galaxies spin.
-That said, black holes at the centers of galaxies are still NOT what hold the galaxies together or cause them to spin. Even supermassive black holes are only a tiny fraction of a galaxy's total mass, you need the gravity from all that mass to hold the galaxy together.
The Sun rotates too, in the same direction that the planets revolve and that most of them rotate. The Sun doesn't rotate as a rigid object, since it is a plasma rather than a solid; its rotation is somewhat faster at its equator than at its poles. But it does rotate, with a period of around 30 days (depending on whether you're closer to the equator or the poles, of course).(15 votes)
Since the Big Bang, the current the composition of the universe has changed. In addition to making “everything else” how has energy, that has been made by the sun, or other stars been made?(3 votes)
you are all very smart. can I get 25 likes pls and thank you? 🥹(4 votes)
why are the orbits of the planets elliptical?(2 votes)
Elliptical orbits are an unavoidable consequence of the fact that the force of gravity is inversely proportional to the square of the distance between two objects.(4 votes)
- Last question on this page I swear =P. So when we say that stars that are red are moving away from us and stars that are blue are moving closer to us, does that mean that galaxies like the blue spiral galaxy in one of the pictures above, are actually moving towards us because of the blue coloration? Or am I not understanding something fundamental?(1 vote)
The star itself is not red, but the light that the star is emitting is red. It only looks red because the star is moving away so the wave lengths are stretched out, or red-shifted. The blue spiral galaxy is blue because the color of the galaxy itself is blue. It might be emitting light that looks red from earth but the color of the actual galaxy is blue.(4 votes)
- How are galaxies formulated?(2 votes)
- is the stars biger then the sun(1 vote)
- In our Solar System the Sun which is a star, is the biggest object. We do not know any planet bigger than the Sun, but we know that far away there are other stars bigger than our Sun and there are some smaller than it.(3 votes)
- heres a vote for you all!(1 vote)
- Do we or are we able to know why Aristarchos' idea of the sun being in the center of the universe didn't catch on? Was the idea too far ahead of his time to be able to appreciate?(1 vote)