The Aurora of April 6th, 2000

Date: 6.4.2000 Time: ~23:00 CEST Exposure: ~30s
Field of View: 93^o x 70^o Emulsion: Kodak Royal Gold 1000 Filter: none
Instrument: f=17mm 1/3.5 Place: Lichtenhagen Observer: T. Credner

Date:	6.4.2000	Time:	~23:00 CEST	Exposure:	~30s
Field of View:	93^o x 70^o	Emulsion:	Kodak Royal Gold 1000	Filter:	none
Instrument:	f=17mm 1/3.5	Place:	Lichtenhagen	Observer:	T. Credner

On April 4th, 2000, a coronal mass ejection was thrown off by the sun and reached Earth two days later. The resulting geomagnetic storm was accompanied by a great display of Northern Lights. The speed of the solar wind increased from a normal value of about 375 km/s to about 600 km/s, thus deforming the shield of the earths magnetosphere in a way that solar electrons could reach the atmosphere above moderate latitudes, for example central europe as can be seen in the image above. Excited oxygen atoms, strucked by solar electrons, account for most of the auroral glow. The often seen green light of wavelength 557.7 nm originates from atmospheric heights of about 110 km, whereas the red glow originates mainly between 200 and 400 km, but both colors come from excited oxygen.