Search results
Results From The WOW.Com Content Network
Scale factor (cosmology) The expansion of the universe is parametrized by a dimensionless scale factor . Also known as the cosmic scale factor or sometimes the Robertson–Walker scale factor, [1] this is a key parameter of the Friedmann equations . In the early stages of the Big Bang, most of the energy was in the form of radiation, and that ...
The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A direct distance measurement of an astronomical object is possible only for those objects that are "close enough" (within about a thousand parsecs) to Earth.
The evolution of the universe and its horizons in proper distances. The x-axis is distance, in billions of light years; the left-hand y-axis is time, in billions of years since the Big Bang; the right-hand y-axis is the scale factor. This is the same model as in the earlier figure, with dark energy and an event horizon.
The enormous ratio of interplanetary distances to planetary diameters makes constructing a scale model of the Solar System a challenging task. As one example of the difficulty, the distance between the Earth and the Sun is almost 12,000 times the diameter of the Earth.
Interstellar travel is the hypothetical travel of spacecraft from one star system, solitary star, or planetary system to another. Interstellar travel is expected to prove much more difficult than interplanetary spaceflight due to the vast difference in the scale of the involved distances. Whereas the distance between any two planets in the ...
The interplanetary medium is responsible for several optical phenomena visible from Earth. Zodiacal light is a broad band of faint light sometimes seen after sunset and before sunrise, stretched along the ecliptic and appearing brightest near the horizon. This glow is caused by sunlight scattered by dust particles in the interplanetary medium ...
The scale factor is a function of time and is conventionally set to be = at the present time. Because the universe is expanding, a {\displaystyle a} is smaller in the past and larger in the future. Extrapolating back in time with certain cosmological models will yield a moment when the scale factor was zero; our current understanding of ...
Distance measures are used in physical cosmology to give a natural notion of the distance between two objects or events in the universe.They are often used to tie some observable quantity (such as the luminosity of a distant quasar, the redshift of a distant galaxy, or the angular size of the acoustic peaks in the cosmic microwave background (CMB) power spectrum) to another quantity that is ...