Feuerkugel 21.9.2006 06:14 MESZ

[Mark Vornhusen]

Hallo,
hab erfahren, dass am 21.9. um 6:14 MESZ von zahlreichen Personen in Dänemark eine Feuerkugel gesehen wurde. Auf der Vechta-Mintron ist diese Feuerkugel vielleicht registriert worden. Jedenfalls gibt es im Nordosten eine verdächtige Strichspur. Die Spur ist nicht durchgehend, weil die Software nur ein Bild pro Sekunde grabbt und mit zunehmender Helligkeit die Kamera auf kürzere Belichtungszeiten als eine Sekunde geht.



Anton wird dazu sicherlich noch etwas schreiben. Es gibt auch eine Webcam-Aufnahme aus Dänemark. Mal sehen, ob das Bild aus Vechta dazu passt oder nicht.


Grüsse,
Mark

[Anton Norup Sorensen]

Thanks for the picture, Mark - could you try to derive some alt/az values from it?

Observations started coming in from our web-form during the morning of sep 21, and this made me check the webcam image archive, which produced the image below:

The image is a stack of 10 FPS recordings, where every other exposure is thrown away. Usually, the camera would have sent an automatic alert, but the brightness of the morning sky had lowered the detection threshold.
First detection: 06:13:37 CET DST Az: 238 Alt: 26.4 (corrected)
Leaving FOV: 06:13:44 CET DST Az: 178 Alt: 46.4

During the next days more than 120 reports were recieved. From these, the map below was made:

The red lines are azimuth angles for visual observations, and the green photographic.
End Az is drawn brighter than start Az.

It is unclear how far south the fireball is, but chances are good that it has been seen by many people in northern Germany.

[Mark Vornhusen]

Dear Anton,
I measured:
Start of first streak: Az: 30° Alt: 17°
End of last streak: Az: 38° , Alt:12°

There are 3 streaks visible. The different lengths and brightness of the streaks is puzzeling. Maybe it slowed down at the end or the exposure time of the camera has changed during the fireball. However the streaks become also shorter because of increasing distance to the camera.

The trail is interrupted because the software grabs only one image every second and the exposure time in twilight is shorter than one second.


Mark

[Anton Norup Sorensen]

I have added the data from the Vechta observation in the figure above.
It really looks like we have two photos of the fireball.
The geographic location used for the Vechta camera is for Vechta town centre:
Long: 8.289 E (8d17m20s) Lat: +52.731 (52d43m52s)

How to interpret the Vechta timestamp of 06:13:45?
Is this the time of e.g. the first or last exposure used in the image?
Can the clock of the webcam be considered precise to about 1 second?
The time is interesting because 06:13:45 is after the meteor disappeared
out of the FOV from Copenhagen, yet the azimuth suggests that what is
photographed is from the beginning of the fireball.
If the recored trails could have appeared 5 to 10 seconds before the timestamp,
things would make better sense.

[Mark Vornhusen]

The timestamp is the time when the sum-image was saved. I save a sum image every 20s. It consists of 20 frames (one frame every second, brightest pixels win, like on your webcam image). So the fireball could have taken place at any time between 06:13:25s and 06:13:45s. The system time of the computer is synchronized with a timeserver. However some seconds drift are possible.
The 3 streaks came from 3 different sum images, each 1s seperated. At night the camera itself goes into a frame integration mode. It delivers only one image every 2.5s. So when I sum every second, I have all objects on the sum image at night. At day the camera delivers 25fps. In this case I sum only every 25th frame and a daylight meteor with a duration of 5 seconds would appear as 5 separeted dots. When twilight starts the camera changes the integration time automatically to shorter times until 25fps is reached.

Mark

[Hartwig Luethen]

Anton, do you have longitude and latitude of your site?
Hartwig

[Hartwig Luethen]

Here is an analysis using UFO orbit for the fireball. The fit is quite good, but orbits cannot be generated due to the poor astrometry and velocity data. However the trajectory in the atmosphere looks quite nice:

Site 1 Kobenhavn
Site 2 Vechta

I could try to improve the fit by using better positions for both sites.


H1 Start = 93.4 km 10.2 deg / 54.81 deg
H1 End = 63.6 km 12.62 deg / 55.6 deg

H2 Start = 90.6 km 10.41 deg / 54.84 deg
H2 End = 78 km 11.40 deg / 54.99 deg


Here is the map UFO orbit provides:



Hartwig

[Anton Norup Sorensen]

Thanks for the analysis, Hartvig!
The last couple of nights I have tried to make something similar manually, or at least put some limits on the quantities. The UFO-orbit analysis looks very reasonable.

My site position is:
Lat 55.698°
Long 12.563°

BTW, I think there is a typing error in the latitude for H1 End above.

[Hartwig Luethen]

The new site coordinates shift the trajectory only slightly:

Site 1 Kobenhavn
Site 2 Vechta

H1 Start = 94.6km 10.16 deg / 54.81 deg
H1 End = 64.3 km 12.6 deg / 55.16 deg

H2 Start = 91 km 10.42 deg / 54.85 eg
H2 End = 78.3 km 11.42deg / 55 deg


Hartwig