Not a relativistic jet, this image of the Andromeda Galaxy is a matter of luck. While the world is recovering from the pandemia, more airplane traces can be found in a single astronomical image. This time, a precise trajectory of a regular flight hit the core of Andromeda Galaxy, M31, while I was capturing data for a deep widefield image of M31. My goal was to capture the so-called Clouds of Andromeda, a recently discovered structure around M31 Galaxy.


I normally apply a rejection algorithm that subtracts the airplane traces, but this time I manually added the plane trace that was captured on a single "lucky" 300" luminance exposure captured the night of the 30th of September 2021.


A deep integration time around Andromeda (M31), using an Ha filter, shows an amazing structure that has been recently called the Clouds of Andromeda. As soon as I saw Rogelio's Bernal 2017 image of Andromeda I knew I wanted to get such a deep view of this area. As the time went by more images appeared, most of them showing a detailed view. This 2021 I acquired a new widefield astrophotography setup specially designed to do this project. It consists of a regular DSLR lens (a Sigma Art 85mm) and a new CMOS camera matched with a full set of filters.

As I started integrating the data in the Ha channel some really faint clouds appeared. But it was not until I got around 30h of data that it was possible to do a full processing of this image. I captured all the Ha data stopping the lens at f/2.8. But the star shapes were not good enough, so I combined the RGB image of the stars captured at f/4.0 (thanks Daniel for this great idea).


About the plane:


I studied the direction of the plane traces in order to know which plane crossed my image. The direction was from west to east,a little bit north from the zenit. Several internet users proposed different flights. I would like to thank a Twitter user, Joan, who pointed out that the plane was a Boeing 737 MAX 8-200 that was covering the route from Lisbon  to Milan (FR2086 flight). It crossed exactly at 20:43 UTC on the 30th of September 2021 above my home observatory in Prades (Tarragona, Catalonia - Spain).

Image details:

L: 35x300" f/2.8
RGB: (33;43;45) x 300″ f/2.8
Ha: 217x600" f/2.8
RGB: (12;10;12)x300" f/4


All images at 120Gain -15ºC bin2
Calibrated with 30 flats (part of the data), 30 darks, 30 dark-flats

Average darkness: 21 mag/arcsec2

Image resolution: 9.12”/pixel 

Data acquisition: September and October 2021.

Ha exposure: 36h10'

Total exposure: 52hTotal



Software: SGP, PHD2, APP, PIX, LR, PS, TPZ. 




Aleix Roig, October 2021.Prades (Tarragona, Catalonia – Spain).