Experiments you can run yourself.
Planetary orbits are elliptical (the Sun at a focus), a planet speeds up at perihelion (second law), and the ratio T²/a³ is constant for the whole system (third law).
The first cosmic velocity v_I=√(GM/R) keeps a body in a circular orbit; the second (escape) velocity v_II=√(2GM/R)=v_I·√2 lets it leave the gravitational field.
For a circular orbit v=√(GM/r), T=2π√(r³/GM). The higher the orbit, the lower the speed and the longer the period. A geostationary orbit has T=24 h.
The H-R diagram plots the temperature and luminosity of stars. Main-sequence stars lie on a single line; more massive ones are brighter and hotter, but live shorter lives.
A star's colour reveals its temperature: hotter stars are blue (Wien's law λ_max=b/T). Luminosity grows as L=4πR²σT⁴ (the Stefan-Boltzmann law).
A nearby star appears to shift against the distant stars over the course of a year. The distance is d=1/p (d in parsecs, p — parallax in arcseconds).
A source's motion changes the observed wavelength of light: Δλ/λ=v/c. Receding → shift toward red (redshift), approaching → toward blue (blueshift).
The farther a galaxy, the faster it recedes: v=H₀·d. The ratio v/d = H₀ is constant — evidence that the Universe is expanding.
A black hole's event horizon has radius R_s=2GM/c². It grows linearly with mass. Nothing escapes from beneath the horizon — not even light (escape velocity > c).
The tidal force (the difference in pull between the near and far sides) grows ∝ 1/r³. Below the Roche limit it tears a moon apart — hence planetary rings.
Apparent brightness falls off with the square of distance: I=L/(4πd²). Twice as far → 4× fainter. That is why a luminous star can look faint from far away.
A heavier planet makes its star "wobble" more strongly — this is how the first exoplanets were detected (Nobel 2019).
Stars orbit an invisible object of millions of solar masses — it is Sgr A* (Nobel 2020).
Distant supernovae show that the expansion is accelerating — dark energy (Nobel Prize 2011).
The regular radio pulses come from a rotating neutron star (Nobel Prize 1974).
Reference card: uniform radiation at a temperature of ~2.7 K as evidence of the Universe's hot beginning (Nobel 1978).
How much would you weigh on the Moon, Mars or Jupiter? See the difference between mass and weight: mass is constant, weight depends on the body's g.
Where do the Moon's phases come from? See that half of the Moon is always lit — only the angle at which we view it from Earth changes.
Why doesn't an eclipse happen every month? See that it takes both alignment (new/full moon) AND the Moon being close to an orbital node.