1. 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 = 10d=1000 pc m-M = 20d=10 5 pc m-M = 30d=10 7 pc

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

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

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

5. 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

6. 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

7. Galaxy Classifications Hubble’s Tuning Fork Sa Sb Sc Sd SBa SBb SBc SBd E0 E6 S0 Irregulars

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

9. cD galaxies Largest Brightest* Diffuse Multiple nuclei Few Mpc size Centers of clusters

10. Spirals S and SB Tightness of arms Size of bulge Sloppy arms

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

12. S0 - Lenticular Spiral-less spirals Disk, no structure Bars

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

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

15. Dwarf Galaxies Irregulars (dIrr) Ellipticals (dE) Spheroidals (dSph)

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

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