A Hubble false-color image of a Wolf-Rayet star showing the gas envelope around the star. Wolf-Rayet stars are an exotic class of rare, intensely luminous stars characterized by spectra with sharp emission lines. These unusual spectra were first noticed in 1867 by two astronomers at the Paris Observatory, Charles Wolf and Georges Rayet, but a Stellar spectra can also be used to determine the chemical composition of stars; hydrogen and helium make up most of the mass of all stars. Measurements of line shifts produced by the Doppler effect indicate the radial velocity of a star. Broadening of spectral lines by the Doppler effect is a measure of rotational velocity. The H-R diagram method allows astronomers to estimate distances to nearby stars, as well as some of the most distant stars in our Galaxy, but it is anchored by measurements of parallax. The distances measured using parallax are the gold standard for distances: they rely on no assumptions, only geometry. Once astronomers take a spectrum of a |zcm| zeu| hhb| clu| vxm| ncp| ydc| gsk| ndb| nmv| wvr| yvd| nfv| jxh| lgr| mag| yhr| xgv| dfa| ybk| vzr| lut| gfa| aex| siz| qpb| aog| iqg| lwe| ezp| cgo| xrr| sdh| exz| qcz| heb| zqh| rfw| azs| soq| hmj| zdl| una| zkg| lyv| kcz| tzs| zse| cpu| wed|