Tag: H-alpha

The Lagoon Nebula in H-Alpha

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The Lagoon Nebula
This image of the Lagoon Nebula was shot from Los Angeles with a DSLR in H-alpha light.

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  • Telescope: Stellarvue SVA130T-IS
  • Mount: Losmandy G-11 with Gemini 2 controller
  • Autoguiding: Yes
  • Optical Configuration: 0.72x field flattener & reducer (f/5)
  • Filter: 12-nm narrowband H-alpha
  • Camera: Canon 60Da
  • Light Frames: 32, 5-min. exposures
  • Calibration: 36 darks, 100 biases, 30 flats
  • Exposure Time: 160 min. (32 x 5 min.)
  • ISO: 800
  • Pre-Processing: PixInsight
  • Processing: Photoshop CC
  • Imaging Location: Los Angeles, Calif.

The Lagoon Nebula is one of the finest examples of a stellar nursery and one of only two nebulae visible to the naked eye. Located in Sagittarius, the nebula lies along the intersection between the galactic plane and the plane of our solar system (ecliptic plane), just a few degrees off a direct line of sight to our galactic center (Sgr A*).

The Lagoon is a giant cloud of dust and gas about 100 ly wide, 50 ly high, and about 4,100 ly away. Peppered throughout its expanse are a number of smaller dark features called Bok globules, which astronomers believe to be stars in the making. These “protostars” consist of dense, light-absorbing balls of gas and dust collapsing under their own weight, a process that also created the open cluster of new stars (NGC 6530) that now makes the whole nebula glow. These new stars are only a few million years old, infants on a cosmological time scale.

Ultraviolet light from NGC 6530 and other stars within the nebula causes the hydrogen gas to glow (fluoresce) in the red. A special narrowband filter placed over the camera sensor lets only this red light through and blocks everything else, which allows emission nebulae like the Lagoon to be photographed from light-polluted cities like Los Angeles.

[For Brian — friend, physicist, outdoorsman. You are greatly missed.]

Categories: Astroimaging

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The Horsehead Nebula…from L.A.

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The Horsehead Nebula
The Horsehead Nebula and Flame Nebula shot with a DSLR from L.A. in H-alpha light

Click for High-Quality Prints

  • Telescope: Stellarvue SVA130T-IS
  • Mount: Losmandy G-11 with Gemini 2 controller
  • Autoguiding: Yes
  • Optical Configuration: 0.72x field flattener & reducer (f/5)
  • Filter: 12-nm narrowband H-alpha
  • Camera: Canon 60Da
  • Light Frames: 12, 4-min. exposures
  • Calibration: 13 darks, 100 biases, 30 flats
  • Exposure Time: 48 min. (12 x 4 min.)
  • ISO: 1600
  • Pre-Processing: PixInsight
  • Processing: Photoshop CC (processed in a single red channel and flattened)
  • Imaging Location: Los Angeles, Calif.

Photographing wispy deep-sky objects (DSOs) in the light-polluted skies of Los Angeles is not for the faint of heart. L.A. was an early adopter of LED streetlights; so night has now become day, ablaze with broadband sky glow. But those gossamer DSOs can be photographed under such conditions, as the image above of the Horsehead Nebula and Flame Nebula proves. The trick is to use a narrowband filter in front of the camera sensor, which blocks all wavelengths of light except the ones of interest. In this case, the wavelength of interest is the red emission line of singly ionized hydrogen at 656 nm…aka, H-alpha. The Horsehead and Flame nebulae both emit at the H-alpha wavelength, so the filter allows their “voices” to be “heard” above the raucous roar of urban light pollution.

This image makes use of a narrowband H-alpha filter with a full-width half-max transmission window of 12 nm. It is a proof-of-concept shot intended to flush out the process and nail down some of the parameters (see bulleted details above). Wind and the meridian precluded taking more light frames, which would have further enhanced the quality and detail of the image. During the imaging session, a very bright LED streetlight gleamed at full intensity about 50 yards away, and the full moon (two days past full) was rising in the east. Yet, the results speak for themselves. It can be done, and done well.

Stay tuned for more narrowband images to come on this website.

Nighttime Lights of L.A.
The city lights of L.A. transform night into day.

Categories: Astroimaging

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