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A light-year, alternatively spelled light year (ly or lyr[3]), is a unit of length used to express astronomical distances and is equal to exactly 9,460,730,472,580.8 km (Scientific notation: 9.4607304725808 × 10 12 km), which is approximately 5.88 trillion mi.
So if the matter that originally emitted the oldest CMBR photons has a present distance of 46 billion light-years, then the distance would have been only about 42 million light-years at the time of decoupling. The light-travel distance to the edge of the observable universe is the age of the universe times the speed of light, 13.8 billion light ...
The Milky Way is approximately 890 billion to 1.54 trillion times the mass of the Sun in total (8.9 × 10 11 to 1.54 × 10 12 solar masses), [7][8][9] although stars and planets make up only a small part of this. Estimates of the mass of the Milky Way vary, depending upon the method and data used.
Andromeda has a D 25 isophotal diameter of about 46.56 kiloparsecs (152,000 light-years) [8] and is approximately 765 kpc (2.5 million light-years) from Earth. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda , which itself is named after the princess who was the wife of Perseus in Greek ...
Multiple other interstellar clouds exist in the region within 300 light-years of the Sun, known as the Local Bubble. [153] The latter feature is an hourglass-shaped cavity or superbubble in the interstellar medium roughly 300 light-years across. The bubble is suffused with high-temperature plasma, suggesting that it may be the product of ...
The cosmic microwave background has a redshift of z = 1089, corresponding to an age of approximately 379,000 years after the Big Bang and a proper distance of more than 46 billion light-years. [79] The yet-to-be-observed first light from the oldest Population III stars , not long after atoms first formed and the CMB ceased to be absorbed almost ...
A growth chart is used by pediatricians and other health care providers to follow a child's growth over time. Growth charts have been constructed by observing the growth of large numbers of healthy children over time. The height, weight, and head circumference of a child can be compared to the expected parameters of children of the same age and ...
For comparison the age of the universe is about 1.38 × 10 10 years. In a vacuum, a photon has two possible polarization states. [ 23 ] The photon is the gauge boson for electromagnetism , [ 24 ] : 29–30 and therefore all other quantum numbers of the photon (such as lepton number , baryon number , and flavour quantum numbers ) are zero. [ 25 ]