Astronomy & Celestial Mechanics
the sky, computed
Concept

Hot spot offset — where it appears

The angle by which the brightest point of a tidally locked planet lies away from the point under its star. Winds carry heated gas downstream before it can radiate, so the peak of its phase curve comes before eclipse. The offset compares radiative and wind timescales.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

One whole orbit. The system's total brightness through one orbit: the transit at phase 0, the slow rise and fall of the planet's illuminated hemisphere between, and the secondary eclipse at phase 0.5 where the planet's own light is removed. The transit is 1.05%; the secondary eclipse is 1800 ppm, about 6 times shallower.

The planet is seen when it disappears

Half an orbit after the transit the planet passes behind its star, and the light that vanishes is the planet's own. Subtracting two brightnesses taken hours apart isolates a body nothing has ever resolved.

exoplanets · Exoplanet atmospheres The same wind flattens the light curve and moves its peak. The planet's bolometric flux through one orbit, from transit at the left edge through eclipse in the middle and back to transit, for ratios of 0.1, 1, 10. The peak falls before eclipse by 3, 27, 72 degrees of orbit, and the fractional amplitude from maximum to minimum is 0.99, 0.92, 0.34.

A peak and an amplitude that should be one number

A hot Jupiter's light rises and falls round its orbit, and the top of that curve comes a little before the planet goes behind its star. The simplest account of why uses one ratio, how fast the air radiates against how fast the wind carries it, and that ratio sets the height of the curve and the place of its peak together. So two measurements have to lie on one line. They mostly do not, and the way they miss says what else is in the air.

exoplanets · Transits

Named alongside it

The objects these essays reach for when they reach for this one.

Phase curveSecondary eclipseAlbedoBrightness temperatureDay night contrastEmission spectrumHeat redistributionHot jupiterOccultationRadiative timescaleTidal locking

All concepts