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READ: Gallery — How Did Our Understanding of the Universe Change?

Browse 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

Source: Big History Project
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

Source: Big History Project
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

Source: Big History Project
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

Source: Big History Project
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

Source: Big History Project
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

Source: Big History Project
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

Source: NASA, ESA, the Hubble Heritage Team
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

Source: NASA, ESA, L. Frattare (STScl), A. Riess (STScl/JHU) and L. Macri (Texas A & M University)
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

Source: NASA
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

Source: NASA/WMAP Science Team
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.

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