[Propagation+Space Weather] Today's SDO Image of the Sun at 304 Angstroms - 2015 Mar 20 20:30 UTC

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Today's Sun (artificially-colored in red) seen at the 304-angstrom wavelength (Extreme Ultraviolet, or EUV), as viewed by the Solar Dynamics Observatory (SDO), by the Atmospheric Imaging Assembly (AIA).

At this wavelength, at a wavelength not seen by the un-aided eye, we can see the Sun through the 30.4 nm (304 A) filter. This Extreme Ultraviolet (EUV) waveband is used to monitor the chromosphere and lower transition region. It is useful to see plasma and filament activity, including filamet eruptions and coronal mass ejections (CMEs).

The image is a "false color image', meaning that observed data are in a range outside of what human eyes can see, so the data are digitally recast into colors that emphasize physically important features. This view is created from data gathered by the Solar Dynamics Observatory (SDO) satellite that flies above Earth's atmosphere in an inclined geosynchronous orbit.

Emissions captured in this image come from helium (He), the second most abundant element in the solar atmosphere. Singly ionized Helium (He II) emits Extreme Ultraviolet (EUV) light when heated to temperatures of ~70,000 deg K. In the upper solar atmosphere the temperatures are so high that most chemical elements have lost many of their electrons. The remaining electron, which is still attached to the atom, emits EUV radiation in narrow wavebands or lines when it is in an excited state.

The 30.4 nm filter (also called channel or bandpass) is dominated by emissions from singly (once) ionized helium which has missing 1 electron--He II. The roman numeral descriptor is consistent with spectral notation: the level of ionization for a given roman numeral is one unit larger that the actual number of missing electrons. The temperatures associated with this level of ionization is range from 6 x 10^4 K to 8 x 10^4 K.

The bright regions in this image correspond to regions of closed magnetic field loops that trap the hot, emitting plasma. Large bright regions are often called active regions. The dark regions correspond to cooler temperatures and possibly to locations where magnetic field lines open into the heliosphere, and thus, do not trap hot plasma.

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