Emission, reflection and dark nebulaes are areas of a galaxy where stars are formed from molecular hydrogen (HII). The Milky Way is littered with dust and an abundance of HII.
Emission nebula glow red because of an HII region becoming ionized by nearby stars. The electons "freed" by this ionization are continually absorbed and reemitted causing it to glow red.
Dark nebulas are cool clouds of dust and molecular hydrogen that can be seen when silhouetted against a bright background (ie. the Horsehead nebula).
Reflection nebula are areas in which material that contain dust is reflected from nearby stars. Because of the shorter wavelength of light this "dusty" area appear blue.
Stars are formed when molecular hydrogen accretes, or falls into itself, gradually increasing in gravity until it reaches a certain mass. As this material continues to fall into itself the temperature and pressure increases until nuclear fusion begins and a star is formed.
A planetary nebula is what forms as a star with a similar mass as our Sun begins to use it's fuel. As hydrogen burns at the core and becomes exhausted the star will "inflate" until it uses up all of it's fuel. It then will expel the outer shell and collapse, and then will start to burn helium. As helium becomes deplete the shell will expand again and the process starts over with lithium until it reaches the 26 element, iron. Iron is the end of the star, it will become a white dwarf and fade out over time.
A supernova remnant is the material expelled from a massive star that burned up all of it's fuel and collapsed onto itself. As a star ages it burns up it's fuel expelling it's outer shell along the way and forming new elements. If the star is so massive (a High Mass Star) it will collapse onto itself as it burns it's fuel. This process continues until it reaches an iron core (element 26). Once it reaches an iron core the fusion process stops and in a matter of seconds gravity causes the star to collapse onto its own weight causing a massive explosion. This explosion creates many of the heavy elements through nucleosynthesis creating the elements heavier than iron. Depending on how massive the star is the final outcome is either a neutron star or a black hole.
For sale is an Astro-Tech 8" f/8 Ritchey-Chretien with Moonlight High Resolution Stepper Motor focuser in excellent condition. I am the only owner and user of this scope and focuser. I have owned this scope from February 2012 to the present and was used primarily for AstroPhotography. This scope is in excellent condition with no scratches on the body. The mirror has no blemishes other than the expected dust on the surface.
Specs from the Astronomics web site:
* 1625mm focal length
* 8 inch f/8 true Ritchey-Chretien hyperbolic mirror optical design
* 0.57 arc sec resolution
* low thermal expansion quartz primary and secondary mirrors
* 99% reflectivity non-tarnishing dielectric mirror coatings
* High strength/low thermal expansion carbon fiber optical tube
* ten contrast-enhancing main tube knife edge light baffles
* two dovetail rails, one Vixen-style and one Losmandy-style "D-plate".
Included with the sale:
*2" extension ring
*Two 1" extension rings
*Moonlight focuser with High Resolution Stepper Motor CS model flange, 1.15" travel brass compression ring drawtube.
***NOTE*** You will need buy the motor controller if planning to use for automation.
Will ship CONUS only. The AT8RC optical tube will ship in the original box. Please email me with any questions.
Hydrogen alpha (Ha) imaging is done through an Ha filter. Hydrogen alpha is a specific wavelength of red light that measures 656.28nm and cannot be detected by the human eye. Hydrogen alpha is highly abundant in space and is the brightest wavelength in stellar astronomy.
Hydrogen alpha filters allows for great detail to emerge from emission nebulas and when added to color images gives great detail to a final image.
Narrowband imaging is ideal for those of us imaging from light polluted skies. Since the Baader Planetarium 7nm Ha filter, used here, blocks out all light except hydrogen-alpha emissions, one can get fine detail without the sensor becoming washed out from the glowing sky.