Hydrogen-alpha All-sky
Overview
The hydrogen-alpha all-sky image is light from a narrow band in the red end of the visible spectrum. We see this light in the composite of visible light, but here we can probe this specific wavelength to see only this small part of red light. It reveals where the glowing hydrogen gas is in the sky.
The night sky in hydrogen-alpha light. Here, we look toward Scorpius and the center of the Milky Way Galaxy. Apart from the band of light along the Milky Way, we also see giant, bubble-like structures. These result from glowing hydrogen gas around supergiant stars.
What Is Hydrogen-alpha?
Hydrogen-alpha, also designated H-alpha or Hα, is a term that describes light from the ground state of the hydrogen atom. When an electron in an atom moves from one energy level to a higher one, we say the atom is excited. But the electron does not move to this higher energy level without the atom absorbing energy from either another atom or a passing photon (packet of light).
Once the atom is excited, it cannot remain in that state for long before it wants to return to its ground state. When the electron moves back down to the lower energy level, light is released at a wavelength commensurate with the energy between the two levels. For the Hα line, this energy difference translates to a wavelength of 656 nanometers in the extreme red end of the visible spectrum. We can see this light with our eyes, but it is lost within the integrated light from the entire visible spectrum.
Spherical Bubbles
The most prominent feature of this image is the ever-present band of the Milky Way. Outside the familiar band of light we see large, round structures of glowing gas. These are actually spherical bubbles that surround supergiant stars. Two prominent examples are Lambda Orionis and Zeta Ophiuchi. The latter appears in the image above as a large, bright, round feature in the top right of the image, centered on the star Zeta Ophiuchi. The former is in the image below, just above image center. The energy coming off these hot, supergiant stars causes the surrounding gas to glow.
Hydrogen-alpha light looking toward the constellation Orion in the night sky. The large, round feature just above center is the hot, glowing gas around the blue supergiant star Lambda Orionis. Barnard’s Loop, the large, arcing nebula, is thought to originate from a supernova and is glowing from the stars in the Orion Nebula. Several other nebulae are visible in this image.
Nebulous Regions
Hydrogen-alpha also reveals nebulous regions to us, mainly where star formation is happening. The Orion Nebula area glows brightly in the image above, along with the Horsehead Nebula and the large, sweeping supernova remnant called Barnard’s Loop. The nebula in Monoceros is also pronounced as one of the brighter points seen in this image.
We can also see that galaxies emit Hα light. The Large and Small Magellanic Clouds in the southern sky glow brightly in this image, and also wisps are visible around the Andromeda Galaxy and the Triangulum Galaxy (M33) nearby.
Profiles
Dossier
Census: |
1 all-sky image |
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Asset File: |
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OpenSpace Version: |
1 |
Reference: |
A Composite H-alpha Template for Microwave Foreground Prediction |
Prepared by: |
Doug Finkbeiner (Princeton), Brian Abbott (AMNH) |
Source Version: |
2.02 |
License: |