APOD: The Flash Spectrum of the Sun (2013 Nov 15)

APOD Robot · Post by **APOD Robot** » Fri Nov 15, 2013 5:06 am

The Flash Spectrum of the Sun

Explanation: In a flash, the visible spectrum of the Sun changed from absorption to emission on November 3rd, during the brief total phase of a solar eclipse. That fleeting moment is captured by telephoto lens and diffraction grating in this well-timed image from clearing skies over Gabon in equatorial Africa. With overwhelming light from the Sun's disk blocked by the Moon, the normally dominant absorption spectrum of the solar photosphere is hidden. What remains, spread by the diffraction grating into the spectrum of colors to the right of the eclipsed Sun, are individual eclipse images at each wavelength of light emitted by atoms along the thin arc of the solar chromosphere. The brightest images, or strongest chromospheric emission lines, are due to Hydrogen atoms that produce the red hydrogen alpha emission at the far right and blue hydrogen beta emission to the left. In between, the bright yellow emission image is caused by atoms of Helium, an element only first discovered in the flash spectrum of the Sun.

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Beyond · Post by **Beyond** » Fri Nov 15, 2013 5:17 am

Now this is an APOD of a different color(s)!

Ann · Post by **Ann** » Fri Nov 15, 2013 5:34 am

I note that the color of the corona is shown as orange, while the integrated color of the solar flash spectrum is likely white.

Or am I wrong to assume that the integrated color of the flash spectrum of the Sun would be white?

Ann

Chris Peterson · Post by **Chris Peterson** » Fri Nov 15, 2013 5:45 am

Ann wrote:I note that the color of the corona is shown as orange, while the integrated color of the solar flash spectrum is likely white.

Or am I wrong to assume that the integrated color of the flash spectrum of the Sun would be white?

What do you mean by the "integrated color of the flash spectrum"?

With a grating, most of the dispersed energy is in the first order diffraction, which is seen here. Some energy is in higher orders, which weren't captured. But the relative energy between different wavelengths is the same in all orders, and in the zero order image of the corona itself. If you took the dispersed image- the spectrum- and reconverged it, the color would be the same as the corona itself, which is orange with this particular sensor.

Guest · Post by **Guest** » Fri Nov 15, 2013 8:39 am

I thought alpha/Lyman emissions of hydrogen line spectra were in the UV. The visible emissions are Balmer line emissions. i.e. the Lyman Alpha are drops from higher electron excited states to level 1 and the the Balmer lines are drops to level 2.
John

Czerno ohoh · Post by **Czerno ohoh** » Fri Nov 15, 2013 8:51 am

What element and transition is responsible for the 3rd brighter (green) line, please?

Ann · Post by **Ann** » Fri Nov 15, 2013 9:07 am

Chris wrote:

/the corona/ is orange with this particular sensor.

So is the corona orange in optical light? Does the corona produce a lot of long-wave optical light, and much less short-wave optical light?

Obviously the corona will be Ha-colored if you photograph it through a Ha filter, and it will be helium-yellow if you photograph it through a special helium filter. Does that mean that it is meaningless to talk about the integrated or "total" optical color of the corona? Can the corona only ever be the color of the narrowband filter through which it has been photographed?

Ann

Boomer12k · Post by **Boomer12k** » Fri Nov 15, 2013 9:14 am

Slices of a "Ring of Light"....

Kind of like a Brain Scan at different levels of the Brain...

:---[===] *

neufer · Post by **neufer** » Fri Nov 15, 2013 12:16 pm

Guest wrote:
I thought alpha/Lyman emissions of hydrogen line spectra were in the UV. The visible emissions are Balmer line emissions. i.e. the Lyman Alpha are drops from higher electron excited states to level 1 and the the Balmer lines are drops to level 2.
John

http://en.wikipedia.org/wiki/H-alpha wrote:
<<H-alpha (Hα) is a specific red visible spectral line in the Balmer series created by hydrogen with a wavelength of 656.28 nm, 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.>>

neufer · Post by **neufer** » Fri Nov 15, 2013 12:44 pm

Czerno ohoh wrote:
What element and transition is responsible for the 3rd brighter (green) line, please?

Magnesium ("triplet" : 516, 517, 518 nm)

http://www.eurastro.de/webpages/MRSPECT.HTM wrote:
The Solar Eclipse 1999 From Hungary
EurAstro Team Szeged I (Manfred Rudolf, Alfred Jakoblich, Franz Michlmayer, Carmen Ortega)

The spectra have been recorded with a 2" spectroscopic grating (200 grooves/mm) which was mounted in front of a 500 mm telephoto lens.

Some prominent emission lines are:

Hydrogen:
. Ha (657nm), H b (486 nm), Hg (434 nm), Hd (410 nm)
He I: 668, 588, 502, 492, 447 nm
Ba II: 650, 614, 493, 455 nm
Na I: 589 nm
Mg I: 553, 516-518 nm ("triplet")
Sr II: 422, 408 nm
Ca I: 586, 423 nm
Ca II: 397,393 nm
Fe I: many lines between 520-570 and 413-430 nm

Spectrum of the chromosphere:

The bright lines in red and turquoise, and two of the blue lines correspond to hydrogen, whereas the yellow line is indicative of helium. Helium was first discovered in 1868 by its yellow emission line in the flash spectrum recorded during a solar eclipse. The wavelength of the emission lines is indicative of the composition (chemical elements) while the intensity of the lines reflects the abundance of the elements (ca. 70% hydrogen, 28% helium, the rest heavier elements). See the emission lines of: Hydrogen (656, 486, 434, 410 nm; indicated by white lines), Helium (587 nm (white line), 502, 447 nm), Sodium (589 nm, close to the yellow helium line), Magnesium (516, 517, 518 nm), Calcium (397, 393 nm). Many of the green lines are due to the presence of iron.

Coronal spectrum

In the spectrum you can distinguish a red, yellow, a faint green, turquoise, and several blue circles. Each of them represents an image of the solar corona in a different wavelength. The red, turquoise, and some of the blue images again are due to the hydrogen emissions, and the yellow image corresponds to helium. The bright dots on the circumference of the solar images represent the prominences. The green emission at a wavelength of 530 nm was first discovered at an eclipse in 1869. An emission line at that wavelength was unknown in laboratory spectra, and a new element was suspected, named "coronium". Later it turned out that this green emission was due to iron atoms from which 13 electrons have been stripped off (FeXIV), and which can only be found under the extreme conditions of the corona at temperatures of 2,000,000 Kelvin or higher. This also makes clear why there are no green "dots" (images of prominences) on the circumference of the green solar image. The temperature of the prominences is about 4000-6000 K only and thus far too low to allow the formation of the highly ionized FeXIV.>>

geckzilla · Post by **geckzilla** » Fri Nov 15, 2013 12:59 pm

I am pretty confused about filters and H-alpha and NII. When I look at Hubble images a lot of times H-alpha will come through the 658 filter and NII through the 656, yet both are called H-alpha filters. Sometimes they look very similar and other times they are quite different, which is really surprising to me considering how close they are. I can't figure out if light gets redshifted slightly or if the filters are just named slightly off or something else I haven't managed to think of.

stephen63 · Post by **stephen63** » Fri Nov 15, 2013 1:30 pm

geckzilla wrote:I am pretty confused about filters and H-alpha and NII. When I look at Hubble images a lot of times H-alpha will come through the 658 filter and NII through the 656, yet both are called H-alpha filters. Sometimes they look very similar and other times they are quite different, which is really surprising to me considering how close they are. I can't figure out if light gets redshifted slightly or if the filters are just named slightly off or something else I haven't managed to think of.

Link to WFC3 filters and bandpass data.

http://www.stsci.edu/hst/wfc3/documents ... tml#370914
Edit: F657N has the bandpass for Hα + [N II]

geckzilla · Post by **geckzilla** » Fri Nov 15, 2013 1:35 pm

Yup, I've been through multiple lists of those. The list doesn't always match up with the descriptions for HubbleSite releases.

stephen63 · Post by **stephen63** » Fri Nov 15, 2013 1:47 pm

geckzilla wrote:Yup, I've been through multiple lists of those. The list doesn't always match up with the descriptions for HubbleSite releases.

I noticed that.

Chris Peterson · Post by **Chris Peterson** » Fri Nov 15, 2013 2:17 pm

geckzilla wrote:I am pretty confused about filters and H-alpha and NII. When I look at Hubble images a lot of times H-alpha will come through the 658 filter and NII through the 656, yet both are called H-alpha filters. Sometimes they look very similar and other times they are quite different, which is really surprising to me considering how close they are. I can't figure out if light gets redshifted slightly or if the filters are just named slightly off or something else I haven't managed to think of.

The lines for [NII] and Ha are only 2nm apart. The camera has very narrow band filters which reasonably isolate the two, as well as a somewhat wider filter between the two that gets both lines. As you note, however, redshift is a factor (or in the case of Doppler shift, blueshift as well). It doesn't take much to shift either line into an adjacent filter. In many cases researchers must use some other information than just the filter to determine what is an [NII] emission area and what is an Ha emission area.

Chris Peterson · Post by **Chris Peterson** » Fri Nov 15, 2013 2:30 pm

Ann wrote:
So is the corona orange in optical light?

Most people see the corona as fairly close to white (that has certainly been my experience). That's just a coincidence of the materials present, however. While the photosphere appears white because it's a near blackbody at about 5800 K, the corona isn't dense enough to act like a blackbody emitter, so we only see the sum of a lot of emission lines.

In this image, we barely see the corona at all. There isn't enough dynamic range. Much of the light very close to the limb is from prominences. And color cameras do a notoriously poor job of capturing color as the eye sees it when the source consists of emission lines (we see that all the time in the inaccurate color of astronomical images captured with color sensors, or in today's image, where the spectrum doesn't look continuous, but more like three nearly uniform red, green, and blue zones, with narrow transitions between them). So to whatever extent we are seeing actual corona in the zero-order image, its color is certainly distorted by the camera sensor in comparison with what our eyes see.

Bottom line: don't expect a camera to produce colors that look much like what you'll experience visually if emission sources are dominant. Most cameras are designed to accurately record continuum sources.

neufer · Post by **neufer** » Fri Nov 15, 2013 2:54 pm

Ann wrote:
So is the corona orange in optical light?

It can be provided the sun is low enough in the sky: http://apod.nasa.gov/apod/ap110115.html

geckzilla · Post by **geckzilla** » Fri Nov 15, 2013 3:08 pm

Chris Peterson wrote:
geckzilla wrote:I am pretty confused about filters and H-alpha and NII. When I look at Hubble images a lot of times H-alpha will come through the 658 filter and NII through the 656, yet both are called H-alpha filters. Sometimes they look very similar and other times they are quite different, which is really surprising to me considering how close they are. I can't figure out if light gets redshifted slightly or if the filters are just named slightly off or something else I haven't managed to think of.
The lines for [NII] and Ha are only 2nm apart. The camera has very narrow band filters which reasonably isolate the two, as well as a somewhat wider filter between the two that gets both lines. As you note, however, redshift is a factor (or in the case of Doppler shift, blueshift as well). It doesn't take much to shift either line into an adjacent filter. In many cases researchers must use some other information than just the filter to determine what is an [NII] emission area and what is an Ha emission area.

Ah, so it's not easy to make the determination or at least it requires one to be careful about it. What about local objects? I know for planetary nebulas both the filters are used a lot. I have no idea whether 2 nm is a lot or a little for nearby things.

Ann · Post by **Ann** » Fri Nov 15, 2013 3:11 pm

neufer wrote:
Ann wrote:
So is the corona orange in optical light?
It can be provided the sun is low enough in the sky: http://apod.nasa.gov/apod/ap110115.html

The entire disk of the Sun looks orange when the Sun is low enough in the sky.

Ann

Chris Peterson · Post by **Chris Peterson** » Fri Nov 15, 2013 3:29 pm

geckzilla wrote:Ah, so it's not easy to make the determination or at least it requires one to be careful about it. What about local objects? I know for planetary nebulas both the filters are used a lot. I have no idea whether 2 nm is a lot or a little for nearby things.

It takes a radial velocity of 1000 km/s to produce a 2 nm Doppler shift. Few local objects have such high velocities. Planetary nebulas typically have expansion velocities around 50 km/s or less. That produces a 0.1 nm shift- easily measured spectroscopically, but insignificant when considering ordinary narrow band filters.

neufer · Post by **neufer** » Fri Nov 15, 2013 3:41 pm

geckzilla wrote:
Chris Peterson wrote:
geckzilla wrote:
I am pretty confused about filters and H-alpha and NII. When I look at Hubble images a lot of times H-alpha will come through the 658 filter and NII through the 656, yet both are called H-alpha filters. Sometimes they look very similar and other times they are quite different, which is really surprising to me considering how close they are. I can't figure out if light gets redshifted slightly or if the filters are just named slightly off or something else I haven't managed to think of.
The lines for [NII] and Ha are only 2nm apart. The camera has very narrow band filters which reasonably isolate the two, as well as a somewhat wider filter between the two that gets both lines. As you note, however, redshift is a factor (or in the case of Doppler shift, blueshift as well). It doesn't take much to shift either line into an adjacent filter. In many cases researchers must use some other information than just the filter to determine what is an [NII] emission area and what is an Ha emission area.
Ah, so it's not easy to make the determination or at least it requires one to be careful about it. What about local objects? I know for planetary nebulas both the filters are used a lot. I have no idea whether 2 nm is a lot or a little for nearby things.

You wouldn't want a relative velocity greater than ~350 km/sec with a very narrow band (i.e., FWHM ~ 1.5 nm) filter.
Hence, most Milky Way objects would be OK.

http://www.sao.ru/hq/lsfvo/devices/scorpio-2/filters_eng.html wrote:
[b][color=#0000FF]The narrow band filters for observation with scanning FPI [/color][/b]
Code: Select all
name	 CWL(Å) FWHM  Tmax(%)
.......................................
FN655	 6559	97	92
.......................................
#76B	  6560	15	71
#77B	  6571	14	76
#78B	  6580	13	69 
Middle-band filters: The set of passband filters with band width 70-200 A is available for observations in the Н-alpha, [SII], [OIII] emission line and in the continuum. The majority of the filters were made by Asahi Spectra USA Inc., the FN674 filter was made by NIIPP (Moscow).

The narrow band filters for observation with scanning FPI : The sets of narrow-band (FWHM=12-25 A) filters are available for observations of galaxies in the [OIII], H-alpha, [NII], [SII] emission limes. You can use this IDL-program to choose the optimal filters for desired systemic velocities.

FloridaMike · Post by **FloridaMike** » Fri Nov 15, 2013 8:59 pm

This has to be the geekiest APOD ever.

geckzilla · Post by **geckzilla** » Fri Nov 15, 2013 9:16 pm

Nah. This one has aesthetic value. This other one was just a chart. It's probably a bit geekier.

Anthony Barreiro · Post by **Anthony Barreiro** » Fri Nov 15, 2013 9:46 pm

I had read that Helium was discovered in the spectrum of the Sun during a total solar eclipse, but I had never seen a picture before. That's pretty cool!

It's deeply troubling, however, that a 19th century scientist, who should have known better, would name a newly discovered chemical element after a god from some superstitious old religion with a geocentric cosmology! Perhaps we can rename this element something more accurate, like "has two protons and doesn't like to bond with other atoms." Although "like" is disturbingly anthropomorphic. What's a poor nomenclaturist to do?

wikipedia wrote:Helios was imagined as a handsome god crowned with the shining aureole of the Sun, who drove the chariot of the sun across the sky each day to earth-circling Oceanus and through the world-ocean returned to the East at night.

geckzilla · Post by **geckzilla** » Fri Nov 15, 2013 9:53 pm

Nobody thinks of that crusty old god anymore. Helios may as well be the god of birthday party balloons and high-pitched voices.

Starship Asterisk*

APOD: The Flash Spectrum of the Sun (2013 Nov 15)

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