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I was just outside between 6:10 - 6:12 a.m. this morning (Sep.11/2021) and between this time saw the strangest anomaly in the sky.

It was still completely dark outside, the stars were extremely clear and I was staring into the sky watching them when I noticed what seemed to be a bright star move up & then down (back to its fixed point) and then, a few seconds later it repeated this motion, always going back to the same fixed point in the sky. A few seconds after that, it slowly started traveling in a smooth straight line (in correlation to the other stars that were in the sky). It was moving from south to north. It travelled for approximately a minute before it slowly faded away. I timed it´s brightest point to its darkest (completely gone) from 8-9 seconds.

There were no lights, no sound, & to high of an altitude to be a plane. I thought, maybe a satellite??? but still puzzled over the fact that it was originally fixed in the sky, & then its motion of moving up and down twice before finally travelling in a linear motion - and also strange, the time it took to fade.

Any explanation of what this could be??
(DD) 38.84561, 0.00037

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    $\begingroup$ If you've ever seen the ISS pass over, you'll notice that when it's low in the sky it hardly appears to be moving at all, but when it's overhead it appears to move very quickly. However, orbiting objects don't reverse direction, so it's more likely to have been something terrestrial, like a drone. Try using Stellarium to see if there were any known satellites in that part of the sky visible from your location this morning. $\endgroup$
    – Aaron F
    Sep 11 at 16:30
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    $\begingroup$ Welcome to Astronomy SE! What is "(DD) 38.84561, 0.00037"? If those are coordinates, which system and which number is which coordinate? Thanks! $\endgroup$
    – uhoh
    Sep 12 at 0:06
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    $\begingroup$ It could have been even the reflection of an airplane that changed bearing. To high altitude to be a plane does not make much an argument, in that context. $\endgroup$
    – Alchimista
    Sep 13 at 9:07
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tl;dr, Like Aaron F mentioned in the comments, this is likely a drone.

Let’s consider why it probably isn’t anything else.

The nearest star to us, Proxima Centauri, is located 1.3 parsecs away from us. To move in such a fashion for an object that far away would require movements faster than the speed of light, which of course is not possible, and thus it cannot be a star.

Satellites, as a general rule, follow orbits for the majority of their lives, with exceptions of course being at the start and end of their lives. It is no small feat to get a satellite approved to go into space, as the country that sends it becomes liable for its behavior and possible affects on property belonging to other countries or private industries. This kind of ragged movements wouldn’t be helpful to get into any specific orbit (since there would be no point in returning to a specific point repeatedly) and while things do go wrong with the process of getting a satellite into its orbit, this behavior is inconsistent with the kind of actions that could or would be taken. As for the end of a satellites life, A similar story can be seen for getting it into a decommissioning orbit.

Other naturally occurring objects are subject to normal gravitational laws, and while there are some interesting naturally occurring effects that arise from the fact that there’s several gravitational forces affecting orbiting bodies (like Lagrange points) the time scales for movements because of those doesn’t line up, nor does the objects final motion.

Finally, there is the idea of a drone. Drones can be very small and quiet, and a close small drone and a far large drone can have the same angular size. The closer the object, the lower the speed necessary to make these movements and appear as they did to you. It also would explain why it faded away, as the light produced from on a drone would be considerably weaker than the light reflected on a satellite from the sun, and especially if the drone was nearby traveling away from you, this would be a consistent scenario.

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Given the time of observation and the fact that the object was "still" than appeared to change direction and finally faded I would say that it was an airplane reflecting the rising sun. This is a common observation about sunrise and sunset. (Like ISS passes. The same principle at work).

edit What seemed the answer, or at least a very reasonable one, it is probably not related to the question posed. A comment made me realise that the (perhaps apparent) behaviour of the light (reflected?) source was more complicated than what I have intended.

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  • $\begingroup$ "...what seemed to be a bright star move up & then down (back to its fixed point) and then, a few seconds later it repeated this motion, always going back to the same fixed point in the sky." $\endgroup$
    – uhoh
    Sep 15 at 21:21
  • $\begingroup$ @uhoh a liner changing bearing can appear to do so. Not to mention a military vehicle. Tough I did not notice the reiteration. I will amend my answer. $\endgroup$
    – Alchimista
    Sep 15 at 22:26

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