Observing Report - Auroral display from Earth encounter with coronal mass ejection (CME) 05/15/2005 7:00 UTC
Pictures were taken at between 07:00 and 09:00 UTC, 5/15/2005 ( 01:00-03:00 AM MDT, 5/15/2005 ) looking from azimuth 0°N to 70°E from N 40.8 Lat. Times are by UTC hour segment unless otherwise noted. See "Log," below for more details. The field-of-view in each image is approx. 30° by 15°.
Exposures made with 1600 ASA film, Pentax MV camera, 30-50 seconds. Reciprocity failure rebalanced with MS-Photoshop. Plate scale can be judged from file 010RP.JPG, above, which shows Vega and the constellation Lyra.
This session began during daylight with white light solar viewing of the purported source of the CME - sunspot 759 - downtown Salt Lake City at 00:00 UTC, 5/15/2005 (06:00pm MDT). Sunspot 759 is a large single spot with a symmetric penumbra. (Modified Zurich class Hhx). Spot 759 is located at about 10° solar latitude. << http://sohowww.nascom.nasa.gov/data/realtime/mdi_igr/512/ >>. It has a roughly circular umbra surrounded by a penumbra band of thickness similar in diameter to the umbra. A 12mm graduated reticule was used make a low-precision measurement of its diameter - about 33 arcsecs for the umbra and 17 arcsecs for one side of the encircling penumbral band, for a total spot size of 66 arcsecs (24,200 kilometers). Sun angular size and physical size at that time awas 1898 arcsec; 696,000, kilometers - implying a sunspot total physical diameter of about 24,200 km, 12,100 km for the umbra and 6,050 km for one side of the penumbra. (As an added bonus, a sundog was seen in a thin cloud bank at around 01:00 UTC (7:00pm MDT).)
At 01:00 AM UTC, I arrived at the observing point to find the auroral display had already begun. This display was principally a continuous faint homogenous Type C (green) skyglow along the northern horizon from W 20° to N 0° to E 70° between 0° and 30° altitude. Through the course of display, the homogenous glow would partially coalesce into faint discrete rayed arcs.
Unusually, Type C skyglow patches formed between 15° to the zenith (90°) in altitude. These lasted between 30-45 secs, with occassional patches lasting for 75 secs.
Type C green aurora are caused by highly excited oxygen at 100-200 km above the surface. Only one instance of faint Type D (red) streaking was seen at the far W 20° azimuth. During part of the display, homogenous Type C arcs started to form on the northern horizon. From the 5-10° angle between the north horizon and the base of these proto-arcs, it was estimated the main auroral band was about 1100 kilometers (685 miles) north of N 41° latitude on the U.S. Canadian border at N 46° latitude.
Brightness varied from International Brightness Codes I (IBC I equal in brightness to the Milky Way) to IBC II (brightness equal to a moonlight cumulus cloud). For comparison, the contrast between the Aquila dark clouds and the Milky Way disk was visible in the south-east sky. Cassiopeia was rising in the bright glow band along the northern horizon. The principal stars of the constellation figure (alf-del Cas) were visible with eps Cas (3.4v) representing a boundary between the visible and secondary invisible Cas stars like zet Cas (3.6v) and iot Cas (4.5v).
One diffuse skyglow patch formed directly over over Lyra. Alf Lyr (Vega, 0.0v) was clearly visible, while gam Lyr (3.2v) and bet Lyr (3.4v) were not.
Although fainter and more diffuse than prior aurora seen at this low-latitude site, the unique feature of this display was its total extended duration with multiple transitions. The display lasted about two and one-half hours. The display repeatedly faded in and out, as described in the following time-based log.
The brightest display was at 8:30-8:45 UTC, which corresponds to the peak magnetic field disturbance (K-index) of 9 reported by the NOAA Space Environment Center reported at 8:49 UTC. (SEC Alert ALTK09, K-index graphic << http://www.sec.noaa.gov/alerts/k-index.html >>.)
35 frames of 1600 ASA film were shot with a 35mm SLR tripod mounted camera. Homogenous faint aurora are a more difficult type of aurora to photograph. This was complicated by the reduced constrast between the display at this site caused by suburban light pollution and the 1st quarter Moon. The intermitent 30-45 second skyglow patch portion of the display was very difficult to photograph. For example, by the time the camera shot could be framed and a 20 second exposure started in the eastern sky, the skyglow patch would dissipate and another patch would form in the north western sky.
|UTC Time||Event type||Notes|
|07:00-07:45||Skyglow patch phase||In addition to the homogenous glow band at the horizon, skyglow patches randomnly formed between azimuth W 20° and E 70° between altitude 20° and the zenith. The skyglow patchs formed beginning at altitude 20° and progressively increased in altitude to the zenith.|
|07:30||North horizon NELM||The principal stars of the Cas (alf-del Cas) were visible with eps Cas (3.4v) representing a boundary between the visible and secondary invisible Cas stars like zet Cas (3.6v) and iot Cas (4.5v).|
|07:35||ZLM measured||5.2v per McBeath visual limiting magnitude area 6 - Hercules.|
|07:45||Skyglow patch over Lyra||alf Lyr (Vega, 0.0v) was clearly visible, while gam Lyr (3.2v) and bet Lyr (3.4v) were not.|
|07:40-08:30||Transition - patch phase ends||The skyglow patch display dissipates. The homogoneous northern glow band begins to intensify from IBC I to IBC 2 and forms proto discrete arcs with some faint rayed-arcs to an altitude of 20°. Some rayed-arcs display moving flame behavior - traveling from azimuth E 20° to E 50°.|
|08:15||Moon set||Moon set, approx.|
|08:30-08:45||Transition - increasing||Formation of faint proto discrete rayed arcs reaches maximum. Skyglow band and some rayed arcs vary from local horizon altitudes of 40° to 70°. Faint red Type D rays seen at azimuth W 20°.|
|08:45-08:50||Transition - fading||Northern skyglow band fades in size to 20° alitude and mag. 4v stars visible in Cas. Northern skyglow band at azimuth N 0° to E 40°. Remaining rayed arcs shift to east with maximal observed eastward arc at due east, azimuth E 90°.|
|08:58-09:05||Transition - increasing||A second lesser crescendo begins to build with faint skyglow and rays reaching altitude of 35°.|
|09:10-09:30||End of display||Northern skyglow band fades with last glow seen around 09:25.|
Kurt Allen Fisher
Salt Lake City, Utah