I started following SpaceX recently.

I used to read the updates but now I am diving deeper to learn new things.

SpaceX is fascinating and I really like everything about it.

But I have question, I don't know if it's stupid but sorry if it is.

What do these images indicate? Is it the trajectory, and why is it like that? Is this just a representation or do they really form due to the launch? Also let me know any extra piece of information you have about this.

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  • $\begingroup$ related but different: How can Flightclub.io Camera Tools be used to simulate launch photography geometry? I'm pretty sure this is an actual photograph, or several stacked together, taken by a fixed camera over a few minutes. The rocket leaves a curved streak as it climbs in altitude and moves downrange. $\endgroup$
    – uhoh
    Mar 15, 2021 at 10:45
  • 2
    $\begingroup$ I once saw a SpaceX launch in Florida. It was night, and fire would've stood out like a sore thumb. It was surprising to find it looking nothing at all like the "messy", chaotic combustion from a traditional NASA ship launching. I was accustomed to the idea of a huge, massive amount of exhaust and fire coming out of things like Apollo ships and space shuttles. But this SpaceX launch looked so clean. In fact, any fire, heated metal, or other light source made the ship look almost angelic. It was different from your picture, but like your picture, it actually looked nice against the night sky. $\endgroup$ Mar 16, 2021 at 19:16

2 Answers 2


As already indicated this is a time lapse exposure of a night time launch highlighting the trajectory of the rocket. A human observer would see a point of light following this trajectory.

The trajectory looks like this due to the multiple factors that affect a rocket leaving the Earth for orbit and how they are balanced.

  1. In order to achieve orbit the rocket needs to be traveling at roughly 7800 m/s parallel to the Earths surface. Much less than this and the rocket will fall back to Earth. But greater than this and the rocket will out run the curvature of the Earth and continuously fall around it.

  2. At high speeds The atmosphere makes life increasingly difficult due to air resistance causing mechanical stress on the rocket and also friction causing energy loss to heat. So it is important to leave the atmosphere rapidly to minimise these effects.

  3. The Earth's gravity tends to force flying objects back to the ground. So its important to reach orbital velocity as quickly as possible to minimise these gravitational losses.

The trajectory seen in the photos is a compromise between these three factors. The rocket starts by heading directly up to escape the deeper layers of the atmosphere, but shortly after launch it slowly starts to incline over towards being parallel to Earths surface so that it can start building up orbital velocity.

The higher it goes the less air resistance there is and the more it can afford to lean. Eventually the rocket is travelling at an steep angle that provides maximum horizontal velocity increase, whilst still providing sufficient vertical component to counteract gravity.

So straight up to start with counteracting forces 2 and 3 then increasingly inclined balancing forces 1 and 3, hence the curved appearance of the trajectory.

The light in the exposure also dims towards the top as at this point the rocket is rapidly getting further from the launch site and is dimming due to distance. The lower part of the curve in the first photo is obviously a reflection in water.

  • $\begingroup$ Plus the top one has a reflection off of water to complicate things a bit... $\endgroup$
    – Jon Custer
    Mar 16, 2021 at 1:30
  • $\begingroup$ Note that even at liftoff, the optimum trajectory isn't exactly vertical. However, a rocket balanced on a launch pad needs to start vertically. A rail-launched rocket can lift off at the optimum angle: en.wikipedia.org/wiki/M-V#/media/… $\endgroup$
    – John Doty
    Mar 16, 2021 at 13:57
  • $\begingroup$ Yes but would suffer from major problems with air resistance $\endgroup$
    – Slarty
    Mar 16, 2021 at 16:28

These are Long-exposure photography. Slow the shutter speed and record the entire rocket launch in one shot. It is common method to record "streaks" of moving bright objects like vehicles on road, star and rockets.



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