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Figure 1.2 The e-m spectrum showing how its generally accepted subdivisions relate to wavelength, frequency and photon energy. or seen directly by the eye, etc.2 For other parts of the e-m spectrum, individual spectra may be produced using detectors that are intrinsically sensitive to different wavelengths, or which may be tuned to scan across a range of wavelengths. Other than for the visual region, spectra are usually shown as a plot of intensity versus wavelength, frequency or photon energy,...

The Unified Model

The bewildering diversity of apparently different AGNs and other types of galaxies (Appendix 2 and earlier chapters) has arisen partly for historical reasons and partly because galaxies and AGNs do have an assort 38The forces exerted by gravity and by radiation pressure both vary as the inverse square (1 d2) of the distance from the central mass or light source. 39This is why the most massive stars that we have been able to discover are only a little over one hundred times the mass of the Sun....

Galaxies and Active Galaxies

Blandford, H. Netzer, L. Woltjer, Springer-Verlag, 1990 Active Galactic Nuclei, Ed J.E. Dyson, Manchester University Press, 1985 Active Galactic Nuclei, I. Robson, John Wiley, 1996 Active Galactic Nuclei From the Central Black Hole to the Galactic Environment, J.H. Krolik, Princeton University Press, 1999 Active Galactic Nuclei in their Cosmic Environment, Eds B. Rocca-Volmerange, H. Sol, EDP Sciences, 2001 Active Galaxies, Open University Worldwide, 2002. Advanced...

Velocities of several thousands of kilometers per second were required The allowed emission lines were produced by

13Remember, the glossary of galaxies and AGN types (Appendix 2) lists a handy summary of these objects and their properties. Figure 3.4 M 77 (NGC 1068) AGN emission lines were observed from this galaxy as early as 1908. It is now classed as a Seyfert type-2 galaxy and is the brightest known example of the type. (Image courtesy of the ING archive and Nik Szymanek.) Figure 3.4 M 77 (NGC 1068) AGN emission lines were observed from this galaxy as early as 1908. It is now classed as a Seyfert type-2...

Almanacs Star Atlases Star and Other Catalogues

Astronomical Almanac, HMSO US Government Printing Office (published annually). Handbook of the British Astronomical Association, British Astronomical Association (published annually). Concise Catalogue of Deep Sky Objects Astrophysical information for 500 galaxies, clusters and nebulae.W.H. Finlay, Springer-Verlag, 2003 Norton's 2000.0, edited by I. Ridpath, Longman, 1998. Sky Atlas 2000.0, W. Tirion, Sky Publishing Corporation, 2000. Sky Catalogue 2000, Volumes 1 and 2, A. Hirshfield and R.W....

Hubbles

Whilst studying the shapes of galaxies and so devising his classification system, Hubble also set about determining their distances and radial velocities. The distances he deduced by the same method that he had used for M 31 by measuring the periods of Cepheid variables within the galaxies. Radial velocities he obtained from the Doppler shifted wavelengths of lines in the galaxies' spectra (Boxes 1.1 and 1.2). By 1929 he had accumulated the distances and velocities for a couple of dozen...

O B A F G K M

As previously mentioned, the inconvenient labels arose historically. The reader may however find the following mnemonic useful Each of these major classes is sub-divided into 10, with each subdivision labeled by a number from 0 to 9. The Sun thus has a spectral class of G2 Sirius (a CMa) is A1 while Antares (a Sco) is M2. The hottest stars known at the moment are O3, while at the cool end, the sequence can be continued beyond M9 into the brown dwarfs. The relationship between surface...

The Milky Way Galaxy

Legend has it that the Milky Way which we see in the sky results from milk spilled from the goddess Hera's breast when the infant Hercules was suckling. While we now know that it is actually formed from tens of thousands of stars too faint to be seen individually with the unaided eye, the legend lives on in the word galaxy itself since that is derived from the Greek word for milk Jtxktx gala . The Milky Way, seen from a good site, is a diffuse and irregular band of light some 10 20 across and...