Here's what a spiral galaxy REALLY looks like. Yesterday, M81 was shown [ http://antwrp.gsfc.nasa.gov/apod/ap960713.html ] in two colors only, but here we see M81 at its most colorful [ http://crux.astr.ua.edu/gifimages/m81series.html ]. In the above picture [ http://crux.astr.ua.edu/gifimages/m81vis.html ], note how blue the spiral arms are - this indicates the presence of hot young stars [ http://antwrp.gsfc.nasa.gov/apod/ap950620.html ] and on-going star formation [ http://antwrp.gsfc.nasa.gov/apod/ap951106.html ]. Also note the yellow hue of the nucleus, possibly designating a population of older stars many billions of years old. M81 [ http://seds.lpl.arizona.edu/messier/m/m081.html ] is actually a dominant member of a group of galaxies which includes M82 [ http://seds.lpl.arizona.edu/messier/m/m082.html ] and several other galaxies. Unlike our Local Group [ http://antwrp.gsfc.nasa.gov/apod/lib/local_group.html ] of galaxies, large galaxies in the M81 group [ http://seds.lpl.arizona.edu/messier/more/m081gr.html ] are actually colliding [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995BAAS%2E%2E18710903L&db_key=AST ]. It is possible that M81's interaction with M82 create the density waves [ http://www.ifa.hawaii.edu/faculty/barnes/ast626/tss.html ] which generate M81's spiral structure.