This movie was made by Dale Cruikshank at the total solar eclipse of August 21, 2017, from Ontario, Oregon. A small transmission diffraction grating about the size of a 35-mm slide was placed in front of the lens of a Canon video camera. The grating was purchased from Edmund Optics for about 50 cents–these are used for classroom demonstrations of spectroscopy.

This movie was taken at twice the usual frame rate and it projects at half the speed of the actual events. Some sections were edited out to minimize redundancy.

The movie begins with a view of the Sun’s continuous spectrum across the visible spectral range of about 400 to 680 nanometers (nm). There are no individual spectral lines visible in the continuum in the partial phases of the eclipse.

As the crescent gets thinner and thinner toward the onset of totality, the continuous spectrum shrinks in width and brightness, and some individual spectral lines begin to appear. These are the hydrogen lines and a helium line. The wavelengths of emission lines from these gases are:

Hydrogen alpha (H-alpha) at 656.3 nm (deep red color)
Helium (He) at 587.5 nm (yellow color)
Hydrogen beta (H-beta)at 486.1 nm (green-blue color)
Hydrogen gamma (H-gamma) at 434.0 nm (violet color)
Magnesium double line at 516.7 and 518.3 nm (green color)

TIMELINE:
00:37 hydrogen and helium emission lines (listed above) just becomming visible
00:42 both H-alpha and H-beta, plus He are clearly visible. The distortions in their shapes are caused by the emission from the prominences protruding over the edge of the Sun. Some weaker emission lines of magnesium and other elements in the green color band are becoming visible. These are from metal atoms in the chromosphere of the Sun. A smudge of violet emission from H-gamma is also becoming visible.
00:46 all the lines are now more prominent, and the shapes of the hydrogen lines reflect the shapes of the prominences in which the emission occurs.
01:01 there are changes occurring in the shape of the H-alpha emission because it is isolated in the prominence at the edge of the Sun.
01:20 this is the spectrum during totality. H-beta is weaker, He is nearly absent, and H-alpha is confined to the prominence.
01:36 those were birds flying over. Also note the powerlines in the foreground. The little white dot at the extreme right-hand edge and below the spectrum is Venus. Note again how the shape of the H-alpha emission has changed.
01:58 The H-beta and He lines are becoming more prominent toward the end of totality.
02:04 H-beta shows the shape of the prominence and He is stronger now.
02:26 Prominent hydrogen and helium lines with the shapes of prominences displayed.
02:45 H-gamma (volet) and magnesium (green) lines are beginning to become prominent.
02:54 All hydrogen and helium lines are prominent, and additional metal lines are emerging in the green region.
03:11 Totality is over and the bright continuum spectrum is back, but H-alpha is still visible.

Posted by: Soderman/SSERVI Staff
Source: Dale Cruikshank

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