Follow-up imaging observations of the first detected interstellar comet 2I/Borisov are presented , which were carried out with the Schmidt-Teleskop-Kamera at the University Observatory Jena in 11 observing epochs in October and November 2019 .
The orbital solution of the comet , derived from the obtained astrometric measurements , confirms its highly eccentric ( e = 3.3570 \pm 0.0006 ) andinclined ( i = 44.0524 \pm 0.0004 ^ { \circ } ) orbit , that proves the interstellar origin of the comet .
According to our best-fitting orbital solution , comet 2I/Borisov reaches its perihelion on 2019 Dec 8 ( q = 2.0066 au ) and its closest encounter with Earth on 2019 Dec 28 ( \Delta _ { \text { min } } = 1.9368 au ) .
The distance corrected brightness of the nucleus of the comet clearly exhibits a linear correlation with its phase angle .
The slope of this correlation indicates the activity of the comet , which is also detected in deep imaging data , taken in 5 observing epochs , showing the coma and the tail of the comet .
During our observing campaign the coma of comet 2I/Borisov exhibits on average a diameter of ( 4.57 \pm 0.38 ) \cdot 10 ^ { 4 } km , and the length of the tail of the comet measures ( 1.52 \pm 0.12 ) \cdot 10 ^ { 5 } km , assuming an anti-solar orientation .