Measurements Magnitudes Apparent magnitude m Absolute magnitude M

Measurements • Magnitudes – Apparent magnitude (m) – Absolute magnitude (M) Distance modulus formula m-M = -5 +5 log (d) d in pc m-M == distance as given by magnitudes m-M = 10 d=1000 pc m-M = 20 d=105 pc m-M = 30 d=107 pc

M related to luminosity Typically luminosity not often quoted. Filters Johnson UBVRIJHKL Mv = Abs. V magnitude V = App. V magnitude B = App. B magnitude Colors B-V, U-B, etc Temperature Dust

• Spectra – Radio – Microwave – IR – Visible – UV – X-ray – Gamma-ray • Environment • Non-thermal – Synchrotron • Spectral Features – Absorption – Emission – Continuous

Velocity - Redshift Low Velocity - Doppler shift formula z is the Redshift (usually) z used as a distance indicator High Velocity – Relativistic Redshift formula

Scales of Distance AU = Astronomical Unit = 150 million km Parsec (pc) = 206, 265 AU = 19 trillion miles Lightyear = 0. 307 pc =5. 9 trillion miles 1 pc = 3. 26 lightyears

Milky Way – 100, 000 ltyr, 30, 000 pc 100 kilolightyears, 30 kiloparsecs (kpc) Largest galaxies = 10 x MW Smallest = 100 pc Sun – MW center = 7. 5 kpc Local Group = 3 million light years = 1 Mpc

Galaxy Classifications • Hubble’s Tuning Fork E 0 E 6 Irregulars Sa Sb Sc Sd SBa SBb SBc SBd S 0

Ellipticals • E# # = 10 (a-b)/a • No systematic rotation axis • Random star motion a b

c. D galaxies • Largest • Brightest* • Diffuse • Multiple nuclei • Few Mpc size • Centers of clusters

Spirals • • S and SB Tightness of arms Size of bulge Sloppy arms

Barred Spirals • • Why? Not always visible Secondary/tertiary 25% - 65% of spirals(!)

S 0 - Lenticular • Spiral-less spirals • Disk, no structure • Bars

Irregulars • Irr I – OB Stars – H II regions – Population I • Irr II – Just plain weird

Sm & Im Irregulars • • Magellanic cloud like Sm – spiral like SBm – barred spiral Im - small

Dwarf Galaxies • Irregulars (d. Irr) • Ellipticals (d. E) • Spheroidals (d. Sph)

Gerard de Vaucouleurs • Sm, Im • Degrees of Bar-ness A-B • Degrees of Ring-ness s-r

Other measurements • Sizes – poorly known • Luminosity Classification I – V Wavelength dependent Galaxy type, structure, content, history – all interrelated – how?