*3759.87 O III* Visible in O stars *3819.61 He I* Strongest in B stars with maximum around B2 *3933.68 Ca II (K line)* First visible around A0. Progressively stronger A1 -> A9 K line = H line(blend) at ~F0 Strongest from G8-K2. *3964.73 He I* Visible in O6-B9, but strongest around B0-B2 *3968.49 Ca II (H line)* Appears blended with adjacent H epsilon until mid F H line(blend) = K line at ~F0 Strongest from G8-K2. *3970.07 H I (H Epsilon)* Hydrogen Balmer Series Reaches Maximum Strength at A0 Can be confused with adjacent Ca II H line, which is strong in cooler stars. *4026.19 He I* Strongest in B stars with maximum around B2 *4030.76 Mn I* Compare to 4130 Si II line for discrimination in F stars *4045.82 Fe I* Visible in F0 and cooler stars. Strongest in K2-K5 Comparison with H I 4101 line gives an indication of spectral type in G stars. They are about equal at G8 *4068.00 C III* Strongest in O stars between O6 and O9 *4073.00 O II* Visible in O9-B2 *4088.85 Si IV* Strongest in O stars between O6 and O9 *4097.33 N III* Visible in B0-B2 *4100.04 He II* Strongest in O stars *4101.75 H I (H Delta)* Hydrogen Balmer Series Reaches Maximum Strength at A0 *4120.82 He I* Strongest in B stars with maximum around B2 Ratio of this line to nearby Si II 4130 provides fine discrimination in this range. Si just visible at B3 *4130.89 Si II* Visible from B2 to A5 Ratio of this line to nearby He I 4121 provides fine discrimination in this range. Just visible at B3. Ratio of this line to nearby He 4144 provides fine discrimination in this range, with maximum of the Si line at B5-B8 Ratio of this line to Mn 4030 line provides discrimination in the F stars. *4143.76 He I* Strongest in B stars with maximum around B2 Ratio of this line to nearby Si 4130. provides fine discrimination in this range, with maximum of the Si line at B5-B8 *4143.88 Fe I* Appear in F0 and cooler stars Strongest in K2-K5 Ratio of this line to H I delta at 4101 is a discriminant They are about equal at G8 *4226.74 Ca I* First a visible around F0. Strenghtens to cooler K and M stars, where it is prominent. In F stars, where the H I (Balmer) lines do not change in strength much, Ca I helps discriminate. Commpare to nearby H I 4340 line; Ca I strengthens as one goes from F0 to F9 In G stars, relative strength of this line to the H 4101 line can be used to determine precise spectral type *4267. C II* Visible from B0-B8, but strongest at B4 *4300.00 CH & Metals (G Band)* First visible around F5 in main sequence stars, and G0 in supergiants. It becomes prominent in cooler stars, G, K, M. *4317.14 O II* Visible in O9-B2 *4340.48 H I (H Gamma)* Hydrogen Balmer Series Reaches Maximum Strength at A0 *4383.56 Fe I* Strongest in K2-K5 *4387.93 He I* Strongest in B stars with maximum around B2 *4471.48 He I* Strongest in B stars with maximum around B2 HeII 4541/HeI 4471 strength is a useful indicator of type between O3-O9 *4471.68 He I* Strongest in B stars with maximum around B2 Ratio of this line to nearby Mg II 4481 provides discrimination around B8-B9 *4481.20 Mg II* Evident in B2-A5; Strongest at A1. Ratio of this line to nearby He I 4471 provides discrimination around B8-B9 *4541.00 He II* Strongest in O stars *4552.62 Si III* Strongest in types B0-B2