Elephant Trunk in H-alpha

The Elephant's Trunk nebula is a concentration of interstellar gas and dust in the star cluster IC 1396 – an ionized gas region located in the constellation Cepheus about 2,400 light years away from Earth. It is commonly called the Elephant's Trunk nebula because of its appearance at visible light wavelengths, where there is a dark patch with a bright, sinuous rim. The bright rim is the surface of the dense cloud that is being illuminated and ionized by a very bright, massive star. The entire IC 1396 region is ionized by the massive star, except for dense globules that can protect themselves from the star's harsh ultraviolet rays.

H-alpha (Hα) is a specific red visible spectral line created by hydrogen with a wavelength of 656.28 nm, is visible in the red part of the electromagnetic spectrum, which occurs when a hydrogen electron falls from its third to second lowest energy level. It is difficult for humans to see H-alpha at night, but due to the abundance of hydrogen in space, H-alpha is often the brightest wavelength of visible light in stellar astronomy.

A hydrogen-alpha filter is an optical filter designed to transmit a narrow bandwidth of light generally centered on the H-alpha wavelength. They are characterized by a bandpass width that measures the width of the wavelength band that is transmitted. These filters are manufactured by multiple (~50) layers of vacuum-deposited layers. These layers are selected to produce interference effects that filter out any wavelengths except at the requisite band.

 

Image Data: Elephant's Trunk Nebula and IC1396

Lens / Scope: William Optics Megrez 102 S.V. with WO Type II 0.8x FF/FR 
Focal Length: 571.2mm 
F/stop: f/5.6 
Exposure: Stack of 30 600-second exposures (5:00 hours total exposure) 
Mount: Sky-Watcher HEQ5 Pro SynScan GOTO (CdC and EQMOD Control) 
Guiding: Sky-Watcher 80 with QHY5 (PHD Control) 
Camera: Canon 500D (Digital Rebel T1i) Baader Mod (EOS Utility Control) 
Mode: RAW 
ISO: 1600
White Balance: Daylight
In-Camera Noise Reduction: Off 
Filter: Omega Optical H-alpha 10nm 
Date: July 22, 2011 
Start Time: 22:50
Location: Beja, Portugal 
Calibration: 30 Darks, 50 Flats, 50 Dark Flats, 50 Bias. 
Processing: Calibrated, aligned and stacked in DSS. Post-processing in Photoshop. GradientXTerminator. Carboni Tools. Noise Ninja.