Vega Through 600 Frames of Starlight

Tonight I pointed the Seestar S50 toward Vega and let it run for a while. Vega is one of those stars that almost feels too bright to photograph properly. It dominates the frame immediately, and after only a few exposures the sensor is already overwhelmed.

The final image came from roughly 600 separate exposures, each around 10 seconds long, so the total integration time ended up being

$$
T \approx 6000\text{s}.
$$

One thing that becomes noticeable during long integrations is how differently a camera experiences the night sky compared to our eyes. At first the image looks sparse and noisy, but as more frames accumulate, faint stars slowly begin to appear from the background. The process feels less like taking a photograph and more like gradually uncovering structure that was already there.

A useful approximation is that the signal-to-noise ratio improves roughly like

$$
\text{SNR} \propto \sqrt{N},
$$

where $N$ is the number of stacked frames. Increasing the exposure time therefore has diminishing returns, but the improvement is still surprisingly noticeable over long runs.

Vega itself remains heavily saturated throughout the integration. The bright halo around the star is not its actual physical size, since Vega’s angular diameter is only about

$$
\theta \approx 3 \text{ milliarcseconds}.
$$

Most of what appears in the center of the image comes from diffraction, atmospheric scattering, and the response of the sensor itself. In some sense the image is recording not only the star, but also the interaction between starlight and the instrument observing it.

What I found most interesting was the surrounding stellar field. Even under moderately light-polluted skies in Mülheim an der Ruhr, the stack eventually became dense with faint background stars that were almost invisible in the early exposures. There is something oddly satisfying about watching the image slowly converge as more photons arrive.

Vega (90 degrees rotated for thumbnail purpose)

I also tried to keep the processing relatively restrained. Long-exposure astronomy already produces enough interesting structure on its own, and excessive editing tends to hide some of the subtlety that makes these images enjoyable to look at in the first place.

Captured with:

Seestar S50
~600 × 10 second exposures
, Germany