## 1 Introduction

A bright daylight fireball appeared on September 12 at 12h49m48s UT, seen by millions of casual witnesses in north western Europe. The event took place over Northern Germany, just south of Denmark (φ = 54.5° N, λ = 9.2° E). The peak brightness was reached at an altitude of 42 km. The fireball had a velocity of 18.5 km/s and had a total impact energy of 0.48 kt (1).

Figure 1 – Map of satellite observed major fireballs.

## 2 Estimating the trajectory

The position differs significantly from an earlier released fireball trajectory based on the visual reports of casual witnesses. Like usually the quality of this kind of data did not allow to compute a reliable trajectory (see Figure 2). Only measurable photographic or video records allow to compute more reliable trajectories. There are a few video records which may help to determine the trajectory. Meanwhile an adjusted trajectory was computed and published by the American Meteor Society:  https://www.amsmeteors.org/2019/09/daytime-fireball-over-north-sea-on-sept-12th-2019/.

## 3 Trajectory and orbit

Dr. Marco Langbroek, expert in this matter, obtained an estimate for the radiant from the velocity vector and computed a heliocentric orbit for this fireball. The satellite data gives only a position for the point of maximal brightness (54.5 N, 9.2 E, 42 km) and a velocity vector. The begin- and endpoint of the fireball are unknown, but the entrance angle and direction are known. The solid line in Figure 4 represents the vector between 80 and 42 km elevation, the dotted line extrapolates this until 27 km elevation. Dr. Marco Langbroek published the following orbital elements:

• A. αg = 183°
• Declination δg = –19.6°
• Velocity vg = 14.8 km/s
• Perihelion distance q = 0.855 AU
• Semi-major axis a = 2.369 AU
• Eccentricity e = 0.639
• Inclination i = 6.96°
• Argument of perihelion ω = 307.838°
• Longitude of the ascending node Ω = 349.202°
• Length of perihelion Π = 297.1°
• Period 3.8 yr

The orbit is an Apollo type orbit, hence asteroidal (Tisserand 3.2), the fireball was caused by an about 2 meter diameter sized asteroidal fragment.

Figure 2 – Erroneous trajectory derived from casual visual witnesses (source: IMO).

Figure 3 – Trajectory computed by Dr. Marco Langbroek.

Figure 4 – Trajectory computed by Dr. Marco Langbroek.

(1) https://cneos.jpl.nasa.gov/fireballs/ (Center for Near Earth Object Studies (CNEOS)).