Stacking

Stacking#

When you’re capturing something faint — like a kilonova at the edge of detectability — a single image often isn’t enough. It might be noisy, unclear, or even completely blank at first glance.

That’s where stacking comes in.

Stacking is the process of combining multiple exposures of the same target to create a single image with less noise and more signal.

Signal vs. Noise#

Let’s break it down:

  • The signal in your image — the light from stars, galaxies, or a kilonova — is real. It stays in the same place in every frame.

  • The noise — from your camera, electronics, or atmosphere — is random. It’s different in every frame.

When you stack images:

  • The signal adds up (gets stronger)

  • The noise averages out (gets weaker)

This improves the Signal-to-Noise Ratio (SNR), making faint objects stand out from the background.

Benefits of Stacking#

  • Makes faint transients (like kilonovae) visible

  • Reveals dim details in galaxies, supernova remnants, or jets

  • Reduces graininess (random noise)

  • Increases photometric accuracy (brightness measurements)

  • Helps confirm if a candidate source is real or just noise

With just one frame, a kilonova might look like random static. But after stacking 5, 10, or 20 frames, it may become unmistakable — a real source that wasn’t obvious before.

How Many Frames Should I Stack?#

There’s no magic number, but here are general guidelines:

Goal

Number of Frames

Bright target photometry

3–5

Faint transient detection

10–30

Deep-sky imaging

30–100+

The more you stack, the better your result — as long as your tracking is solid and the frames are well-aligned.

Tools for Stacking#

Most amateur-friendly tools support stacking automatically:

  • ASTAP: Fast, automatic star alignment and stacking

  • Prism: Scripted stacking during preprocessing

  • Siril: Powerful stacking and preprocessing workflow

  • DeepSkyStacker: Easy visual interface for stacking

Each has options for median, average, or sigma-clipping stacking, depending on your goals and number of frames.

More frames = more signal = better science.

Stacking is a key part of transforming raw, noisy exposures into meaningful data!

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