How far can you see? The most distant object easily visible to the unaided eye is M31 [
http://www.seds.org…], the great Andromeda Galaxy [
http://www.seds.org…] some two million light-years away. Without a telescope, even this immense spiral galaxy appears as an unremarkable, faint, nebulous cloud in the constellation Andromeda [
http://www.astronom…]. But a bright yellow nucleus, dark winding dustlanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital [
http://www.geocitie…homepage.html ] mosaic of the nearby island universe. While even casual skygazers [
http://badastronomy…] are now inspired by the knowledge that there are many [
http://antwrp.gsfc.…] distant galaxies like M31, astronomers seriously debated [
http://adsbit.harva…nph-iarticle_query?1 995PASP..107.1133T ] this fundamental concept only 80 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis [
http://antwrp.gsfc.…debate20.html ] debate [
http://antwrp.gsfc.…] of 1920, which was later resolved by observations [
http://antwrp.gsfc.…] of M31 in favor of Andromeda, island universe [
http://www.astr.ua.…].
Explanation
How far can you see? The most distant object easily visible to the unaided eye is M31 [
http://www.seds.org…], the great Andromeda Galaxy [
http://www.seds.org…] some two million light-years away. Without a telescope, even this immense spiral galaxy appears as an unremarkable, faint, nebulous cloud in the constellation Andromeda [
http://www.astronom…]. But a bright yellow nucleus, dark winding dustlanes, gorgeous blue spiral arms and star clusters are recorded in this stunning telescopic digital [
http://www.geocitie…homepage.html ] mosaic of the nearby island universe. While even casual skygazers [
http://badastronomy…] are now inspired by the knowledge that there are many [
http://antwrp.gsfc.…] distant galaxies like M31, astronomers seriously debated [
http://adsbit.harva…nph-iarticle_query?1 995PASP..107.1133T ] this fundamental concept only 80 years ago. Were these "spiral nebulae" simply outlying components of our own Milky Way Galaxy or were they instead "island universes" -- distant systems of stars comparable to the Milky Way itself? This question was central to the famous Shapley-Curtis [
http://antwrp.gsfc.…debate20.html ] debate [
http://antwrp.gsfc.…] of 1920, which was later resolved by observations [
http://antwrp.gsfc.…] of M31 in favor of Andromeda, island universe [
http://www.astr.ua.…].
Explanation
