A star's rotational light curve is a linear measurement of its surface. Paint spots
below and watch the light curve appear. Then press
“randomise the invisible part”: the surface will change completely
and the light curve will not move at all. That residual is the operator's
null space, and on a real survey cadence it is over 99% of the map.
Drag on the left-hand map to paint. Shift-drag makes a bright feature.
real epochs
distinct nights
map pixels
modes with SNR > 1
null fraction
your map: invisible power
Your surface, split by what the data can determine
1 · the surface (paint here)
Equirectangular map. The shaded band near the bottom is the
polar cap that is never visible at this inclination.
2 · what the data determines
The projection onto the operator's row space — everything a
light curve can ever constrain, at any signal-to-noise.
3 · what only a prior can supply
The null-space residual. Add any amount of this and the light
curve is unchanged. Every published spot map lives largely here.
The light curve
light curve of your surfaceafter randomising the invisible partper-epoch error bar
Real posteriors: swap the prior, keep the data
These are not simulated in the browser — they are posterior means
from the actual diffusion runs, under two deliberately different prior
hypotheses (a smooth isotropic field vs. dark localised spots) on identical
data. The data-constrained parts agree; the null-space parts do not.