The Sun & Solar Activity

  The Sun as a star   Structure of the Sun   The Solar Cycle   Solar Activity   Solar Wind   Observing the Sun

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Observing Different Layers of the Sun

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Observing Different Layers of the Sun

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Observations: Overview

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 White light

 Filtered light

 X-Rays

 Magnetograms

 Dopplergram

Lick Telescope at the Lick Observatory, CA

Observations: Overview

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  White Light

Two different methods for observing - ground and space based

Essentially an intensity-gram that indicates temperature Courtesy of SOHO

Observations: Overview

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  White Light

Both ground and space based telescopes work on the same principles -- magnifying and focusing light onto a ‘recorder’.

http://www.synapticsystems.com/sky/scopes/telbasic.html

These images and more details on telescope basics:

Observations: Overview

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  White Light

Both ground and space based telescopes work on the same principles -- magnifying and focusing light onto a ‘recorder’.

Observations: Overview

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  White Light

Both ground and space based telescopes work on the same principles -- magnifying and focusing light onto a ‘recorder’.

Observations: Overview

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  White Light

The recorder can be the human eye, film, or most often a CCD that directly detects photon counts over a grid and reports it to a computer.

Hubble Space Telescope (essentially a giant light bucket)

Where CCDs for various instruments are attached

Observations: Overview

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  Observing Technique

A coronagraph essentially acts as an artificial eclipse, blocking out the main disk of the Sun and enabling observations of the corona and energetic but diffuse signatures of events such as flares and coronal mass ejections as they escape from the Sun.

Observations: Overview

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 Filtered light Works on the same principles as white light, except for a specific wavelength or bandwidth that is filtered out of the full spectrum. These can be outside the visible, for instance in the UV, EUV and IR. The various instruments on Hubble allow different wavelengths to be observed, from ~200 nm (UV) to 2400 nm (IR). Remembering that the visible spectrum lies between ~400-700nm.

Observations: Overview

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 Filtered light UV and EUV cannot be observed through the Earth’s atmosphere since those wavelengths are mostly absorbed/scattered -- only a fraction get through. Hence to study the Sun and other sources of UV light space based telescopes are needed (such as Hubble).

Observations: Overview

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  X-Rays Similar observation/telescopic techniques as white light and UV, but with more sophisticated filtering for these high energy photons. Can similarly filter different wavelengths just as with the lower energy end of the electromagnetic spectrum. Also, must be observed from space due to the Earth’s atmosphere blocking most of these wavelengths.

GOES 12 - Notice the Venus transit across the southern hemisphere blocking X-Rays from reaching the satellite at Earth.

Observations: Overview

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 Magnetograms

By measuring the strength of the Zeeman splitting for given known transitions (here Lyman α for hydrogen is shown, electron moves from n=2 to n=1), a measure of the magnetic field strength and orientation can be obtained.

Zeeman splitting

Solar Activity

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Strong B-field splits spectral lines according to strength

Observing Spectra - line splitting from the Zeeman effect

Observations: Overview

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 Magnetograms

By measuring the strength of the Zeeman splitting for given known transitions a measure of the magnetic field strength and orientation can be obtained and mapped… here black and white represent line of sight orientation, grey represents BLoS = 0.

Stanford Solar Center

Observations: Overview

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 Magnetograms

Sunspots are visible in magnetograms because they are essentially eruptions of magnetic field from the surface (where the field is wrapped along the surface with little to no component on the line of sight).

Line of Sight

Observations: light vs. magnetic field

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