Can humans detect alien megastructures?

Yes — humans can detect candidate alien megastructures, but we generally cannot confirm one is artificial from a single observation.

The main idea is to look for technosignatures, especially:

1. Excess infrared emission
   A very large structure that captures starlight would likely reradiate some of that energy as heat, which could appear as unusual infrared light. Infrared surveys and telescopes such as WISE and JWST can help look for stars or systems with abnormal infrared output, though such signals can also have natural explanations.

2. Unusual dimming patterns
   If a large artificial structure passed in front of a star, it could produce irregular or asymmetric dips in brightness rather than the smooth dip expected from a planet. Transit surveys such as Kepler and TESS can find these kinds of anomalies.

A famous example is Boyajian’s Star, which showed very unusual dimming events, including dips reported as large as about 22%. It attracted interest as a possible technosignature, but the leading explanations today involve dust and other natural causes rather than a megastructure.

The main limitation is that natural phenomena can mimic these signals — for example dust clouds, comets, debris disks, or unusual stellar variability. So far, no observed anomaly has been confirmed as an alien megastructure.

So the short answer is: yes, humans can detect suspicious signals that might indicate megastructures, but proving an artificial origin is much harder.