Proper Distance Vs. Comoving Distance From Small Galaxies To Galaxy Clusters
Within small distances and short trips, the expansion of the universe during the trip can be ignored. This is because the travel time between any two points for a non-relativistic moving particle will just be the proper distance (i.e. the comoving distance measured using the scale factor of the universe at the time of the trip rather than the scale factor "now") between those points divided by the velocity of the particle. If the particle is moving at a relativistic velocity, the usual relativistic corrections for time dilation must be made.
Read more about this topic: Comoving Distance
Famous quotes containing the words proper, distance, small, galaxies, galaxy and/or clusters:
“Television programming for children need not be saccharine or insipid in order to give to violence its proper balance in the scheme of things.... But as an endless diet for the sake of excitement and sensation in stories whose plots are vehicles for killing and torture and little more, it is not healthy for young children. Unfamiliar as yet with the full story of human response, they are being misled when they are offered perversion before they have fully learned what is sound.”
—Dorothy H. Cohen (20th century)
“I am considered a misanthropist now and then, because I do not socialize with many people. But it’s only my mind that avoids you, my heart is still with you, and seeks the distance so that it can keep on loving you.”
—Franz Grillparzer (1791–1872)
“Man staggers through life yapped at by his reason, pulled and shoved by his appetites, whispered to by fears, beckoned by hopes. Small wonder that what he craves most is self-forgetting.”
—Eric Hoffer (1902–1983)
“Don’t you see what’s at stake here? The ultimate aim of all science—to penetrate the unknown. Do you realize we know less about the earth we live on than about the stars and the galaxies of outer space? The greatest mystery is right here, right under our feet.”
—Walter Reisch (1903–1963)
“for it is not so much to know the self
as to know it as it is known
by galaxy and cedar cone,
as if birth had never found it
and death could never end it:”
—Archie Randolph Ammons (b. 1926)
“Where we such clusters had,
As made us nobly wild, not mad;
And yet each verse of thine
Outdid the meat, outdid the frolic wine.”
—Robert Herrick (1591–1674)