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- Edwin Hubble
- an American astronomer, Hubble (November 20, 1889 – September 28, 1953) profoundly changed our understanding of the nature of the universe by demonstrating the existence of other galaxies beyond the Milky Way. The Hubble Space Telescope is named after Edwin Hubble.
- Einstein Cross
- also known as G2237+0305, is an example of gravitational lensing, where a foreground galaxy has produced four images of the same quasar that lies directly behind the galaxy.
- Einstein’s Field Equation
- describes gravity as the curvature of space-time dependent on the mass that exists in it.
- Electrode
- a collector of electronic charge.
- Electromagnetic Force
- the electromagnetic (or EM) force is one of the four known universal forces, along with gravity and the strong and weak nuclear forces. The EM force holds all the molecules and cells in your body together and is the result of interactions between charged particles (protons and electrons) within the atoms and molecules.
- Electromagnetic Spectrum
- the full range of wavelengths (or, equivalently, frequencies), from radio waves to gamma rays, that characterizes light.
- Electron
- a negatively charged subatomic particle.
- Electron Volt (eV)
- a unit of energy commonly used in astronomy. A typical gamma ray has an energy of about 100 million electron Volts (100 MeV).
- Ellipse
- a closed shape with two focal points such that the sum of the distances from the edge to the points is constant.
- Elliptical Galaxy
- these galaxies range in shape from nearly spherical to flattened disks. They are characterized by a much older population of stars. They also have very low rates of star formation, meaning very few stars are being born here. Ellipticals contain little or no cool gas or dust.
- Energy Flux
- the energy per second that is deposited onto a given area. For instance, the energy per second deposited on a square-meter sized detector. Since all photons do not have the same energy, the energy flux and photon flux are not necessarily the same. The SI unit for energy flux is watts per square meter [W/m2]. At the top of Earth’s atmosphere, the flux from the Sun is about 1300 W/m2.
- Equation
- an equation is a mathematical way of saying that two expressions are equal. Newton’s Second Law of Motion, F = ma, is an equation.
- Equatorial Radius
- the radius of the Sun measured from its center to its equator. This is not the same distance as measuring from the center to the pole. Since the Sun is spinning, it is slightly flattened, causing the equator to bulge slightly outward and the poles to move slightly inward. The Sun’s shape is sort of like the shape you get when you hold a spherical balloon on opposite sides and then squeeze it slightly inward.
- Equatorial Coordinate System
- A geocentric coordinate system used for measuring the angular positions of celestial objects. The system’s angular coordinates are right ascension and declination.
- Evolutionary Computing
- a form of computer programming that mimics the adaptive abilities of species on a genetic level. The technique is used in problem solving and data correlation.
