es of room forinterpretation. Imagine standing in a field at nigrying to decide ant electric ligraigools of astronomy you can easilyenougermine t tness and t one is, say, 50 percent moredistant t be certain of is ussay, a 58-t bulb t is 122 feet at lig is 119 feet, 8 incop of t you must make alloortions caused by variations in tmospergalactic dust, contaminating ligars, and many otors. t is t your computations are necessarily based on a series of nestedassumptions, any of ion. taccess to telescopes is al a premium and orically measuring red ss ably costly in telescope time. It could take all nigo get a single exposure. Inconsequence, astronomers imes been compelled (or o base conclusionson notably scanty evidence. In cosmology, as t Geoffrey Carr ed, on a molein Rees it:
“Our present satisfaction [ate of understanding] may reflect ty of taratheory.”
tainty applies, incidentally, to relatively nearby to tantedges of tes, t-years a do not often stress to t it is someitled to exactly by quot;a constant of 50quot; or quot;a constant of 100.quot; tronomical units of measure. Except conversationally, astronomers dont use ligance called traction of parallax and second), based on a universal measure called tellar parallax and equivalent to 3.26 ligant is expressed in terms of kilometers per second per megaparsec.
tronomers refer to a ant of 50, ;50 kilometers per second permegaparsec.quot; For most of us t is of course an utterly meaningless measure, but tronomicalmeasures most distances are so o be utterly meaningless.
quite t large, matters are naturally magnified. Bearing allt in mind, t bets to be fixed on a range ofabout 12 billion to 13.5 billion years, but y.
One interesting recently suggested t t nearly as big as , t ance some of tions, g images created by rebounded light.
t is, t deal, even at quite a fundamental level, t knoleast ists calculate t of matter needed toogetely s. It appears t at least 90 percentof t, is