Keys To Soho Daily Pictures

Soho is a cooperative European Space Agency (ESA)/NASA solar observation satellite. It's observing the Sun from an orbit which is located about the Lagrangian point L1. It's providing professional and amateur astronomers with data, of them daily pictures. These daily Soho images, found on the SOHO website, are taken through various instruments. They may help building a comprehensive view of the Sun, starting at the photosphere, this surface by which our star is seen in the visible wavelengths of the spectrum, up to the corona

LASCO layer: corona	C3 (30 million miles (45 million km))
	C2 (5.25 million miles (8.4 million km))
ETI layer: lower corona (or upper chromosphere)	EIT 284 (t 2.0-2.5 million ° K)
	EIT 195 (t 1.5 million ° K)
	EIT 171 (t 0.9-1 million ° K)
	EIT 304 (t 60,000-80,000° K)
MDI layer: photosphere (magnetogram, left; visible, right)
pictures courtesy SOHO daily pictures

The photosphere is shown by the "MDI continuum" and the "MDI magnetogram" pictures. MDI stands for "Michelson Doppler Imager". The orange picture is almost like the Sun is looking naked-eye, limb-darkening excepted. The usual photosphere activity is shown (sunspots, faculae), as the magnetogram is showing areas of magnetic activity (white indicates a north polarity as black a south one). Most of such areas are linked to sunspots seen in the visible. Some are not associated with any sunspot however. Such areas are useful too to either track a sunspot which decayed or to anticipate where one sunspot might develop. The temperature at the photosphere is 6,000° K

The "Extreme ultraviolet Imaging Telescope" (EIT) is providing four color images. The EIT is imaging the Sun in the extreme ultraviolet as each image pictures one layer of the inferior strates of the corona (or, which is about the same, all the pictures are about the upper chromosphere). The picture are ranging from the lowest, to the highest level, in this order (the higher a layer, the hotter it is):

• the orange picture (EIT 304 angstroms) matches a layer with a temperature of 60,000-80,000° K, comprising singly ionized helium
• the blue picture (EIT 171 angstroms) is a layer with a temperature of 0.9-1 million ° K and with the 8 to 9-time ionized iron
• the green picture (EIT 195 angstroms) is 1.5 million ° K and matches a layer with the 11-tims ionized iron
• the yellow picture at last (EIT 284 angstroms) is for a layer with a temperature of 2.0-2.5 million ° K and the 14-time ionized iron

The "Large Angle Spectrometric Coronagraphs" (LASCOs) are coronagraphs, that is an occulting disk which creates an artificial eclipse. Such a tool, available for ground-based instruments too, is allowing to see the features which are seen during a total solar eclipse. The LASCO pictures are showing the corona with the coronal streamers, those nearly radial bands. Occasionally, a Coronal Mass Ejection (CME) can be seen being expelled from the Sun and crossing the field of both coronagraphs. The LASCO C2 (red picture) is showing the inner corona up to 5.25 million miles (8.4 million km) as the LASCO C3 (blue picture) is encompassing 30 million miles (45 million km), that is about half the orbit of Mercury. The white circle on the LASCO images is the actual size of Sun's disk as the dark pole is the is the occulter disk's pole. The LASCO C3 images are allowing too to see the background stars as, celestial mechanics permitting, both inferior (Mercury and Venus) and superior (starting at Mars) planets may be seen at their conjunctions