Astronómia a fyzika Zeme
What you must know
Expect the basics of the solar system (planets, Kepler's laws, the Sun as an energy source), stars and stellar evolution, galaxies, and the scale of the universe. For Earth physics, know the seasons (caused by axial tilt, not distance), day and night, phases of the Moon, eclipses, and Earth's magnetic field. Kepler's third law (T² ∝ a³) and Newton's gravitation (F = GMm/r²) are frequent quantitative items.
Traps
- Claiming seasons are caused by Earth's varying distance from the Sun - they are caused by the ~23.5° axial tilt.
- Confusing solar and lunar eclipses (which body is in which shadow).
- Forgetting that Kepler's third law relates period squared to semi-major axis cubed.
- Mixing up a light-year (distance) with a year (time).
- Thinking the Moon always shows the same face because it does not rotate - it rotates once per orbit.
Worked example
Compare orbital periods of two planets with semi-major axes 1 AU and 4 AU. Kepler: T² ∝ a³, so T ∝ a^(3/2). For a = 4 AU, T ∝ 4^1.5 = 8, so the period is 8 Earth years. This proportionality is quicker than recomputing with GM.
Rule of thumb: light-year is a distance (~9.46 × 10¹² km). For any orbital question, write Kepler's third law and express the ratio T₂/T₁ = (a₂/a₁)^(3/2).