Detail View: NASA Astronomy Picture of the Day Collection: Emission and Reflection in NGC 6559

Title: 
Emission and Reflection in NGC 6559
Explanation: 
Bright gas and dark dust permeate the space between stars in a nebula known as NGC 6559 [ http://robgendler.astrodigitals.com/6559.html ]. The gas, primarily hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ], is responsible for the diffuse red glow of the emission nebula [ http://antwrp.gsfc.nasa.gov/apod/emission_nebulae.html ]. As energetic light from neighboring stars ionizes interstellar hydrogen [ http://antwrp.gsfc.nasa.gov/apod/ap010113.html ], protons [ http://www.neutron.anl.gov/hyper-physics/proton.html ] and electrons [ http://www.aip.org/history/electron/ ] recombine to emit light [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] of very specific colors [ http://csep10.phys.utk.edu/astr162/lect/light/absorption.html ], including the red [ http://antwrp.gsfc.nasa.gov/apod/ap010214.html ] hue observed. Small dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] particles reflect blue starlight efficiently and so creates the blue reflection nebulosity [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ] seen near two of the bright stars. Dust [ http://nedwww.ipac.caltech.edu/level5/Mathis/Mathis9.html ] also absorbs visible light, causing the dark clouds [ http://antwrp.gsfc.nasa.gov/apod/ap010923.html ] and filaments [ http://antwrp.gsfc.nasa.gov/apod/ap990919.html ] visible. NGC 6559 [ http://www.aao.gov.au/images/captions/uks003.html ] lies about 5000 light-years [ http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question19.html ] away toward the constellation of Sagittarius [ http://www.astronomical.org/constellations/sgr.html ].
Credit and Copyright: 
Robert Gendler [ mailto:robgendler@worldnet.att.net ]
keyword: 
NGC 6559
facet_where: 
Goddard Space Flight Center (GSFC)
facet_what: 
New General Catalogue (NGC)
original url: 
http://antwrp.gsfc.nasa.gov/apod/ap011023.html
UID: 
SPD-APOD-ap011023