Astronomy
Observing basics
Celestial sphere, coordinates, telescopes, spectra.
Basics
Celestial sphere
Right ascension and declination are sky longitude and latitude (equatorial). Altitude and azimuth are local horizontal coordinates. Earth’s rotation makes stars rise east and set west. The ecliptic is the Sun’s path, tied to the seasons.
Telescopes
Collecting area scales as aperture squared. Diffraction-limited resolution ≈ 1.22 λ / D. Seeing limits ground optical work. Radio, IR, and X-rays need special windows or space. Spectra give elements and Doppler speed.
Moon and eclipses
Synodic month ≈ 29.5 days. Eclipses happen near the nodes, when Sun, Moon, and Earth nearly align. A total solar eclipse has a narrow lunar shadow; a lunar eclipse can cover the whole Moon in Earth’s shadow.
Formulas
Diffraction limit
Larger D and shorter λ resolve finer angles.
Symbols
-
Daperture diameter
Radial velocity (non-rel.)
Redshift means receding. Basis of the radial-velocity exoplanet method.
Symbols
-
Δλwavelength shift
Small-angle size
Links angular size, physical size, and distance.
Symbols
-
strue transverse size -
ddistance
Key table
| Polaris | near the north celestial pole now — altitude ≈ latitude |
|---|---|
| Light pollution | Cities drown faint nebulae and galaxies |
In this field
Solar system
Planets, Kepler, gravity, escape speed.
Stars
HR diagram, fusion, lifetimes, magnitude.
Galaxies and cosmology
Galaxies, Hubble, redshift, black holes.
Exoplanets and life
Detection, habitable zone, a SETI sketch.
The Sun and space weather
Solar structure, spots, flares and CMEs.
Moon, tides, and eclipses
Lunar phases, tides, and solar and lunar eclipses.
Magnitudes and spectra
Apparent and absolute magnitude, distance modulus, colour and spectral type, Wien’s law.
Galaxies and Hubble
Galaxy shapes, rotation curves, the Hubble–Lemaître law, and a standard-candle sketch.
Telescopes and light
Aperture, diffraction limit, collecting area, seeing versus space telescopes.
Stellar death
Red giants, supernovae, and sketches of white dwarfs, neutron stars, and black holes.