← INDEX — FIG. 00 — SUNLIGHT, TAKEN APART 1966 SOLAR ATLAS · 380–700 nm

SPECTRUM
SPECTROSCOPY: WHAT STARLIGHT SAYS

Spreading starlight into a rainbow and reading its dark lines.

BEGIN — CHAPTER 01 →

CH.01 / 10 — CAMBRIDGE, 1666

White light is a mixture

Newton's prism, 1666 [1].

Experimentum crucis [1].

NEWTON'S OWN NUMBERS

length of the band 2° 49′ ÷ width of the Sun 31′ = 169′ ÷ 31′ ≈ 5.5

Band ÷ Sun ≈ 5.5.

CH.02 / 10 — MUNICH, 1814–17

Hundreds of gaps in the rainbow

About 574 lines between B and H [2].

Lamp line at D; Sirius stripes [2].

FOUR OF FRAUNHOFER'S LETTERS, IDENTIFIED LATER

C 656.3 nm hydrogen · D 589.0 + 589.6 nm sodium · F 486.1 nm hydrogen · H 396.8 nm ionized calcium (with K, 393.4 nm)

Identified later [4][5][8].

CH.03 / 10 — HEIDELBERG, 1859–60

Every element writes its own lines

Kirchhoff and Bunsen, 1860 [3][4].

The D lines got darker [4].

HOW STRONG IS A DARK LINE? — EQUIVALENT WIDTH

W = width of a perfectly black, sharp-edged line that removes the same light · 1 mÅ = 0.0001 nm

Atlas definition [5].

Atlas [5]; NIST lines [6].

CH.04 / 10 — GUNTUR · LONDON, 1868 — LONDON, 1895

An element found in the Sun first

Janssen and Lockyer, 1868 [8].

Helium on Earth, 1895 [8][9][10][11].

CLOSE TO D, BUT NOT D

D₂ 588.995 nm − D₃ 587.562 nm = 1.433 nm · D₁ − D₂ = 589.592 − 588.995 = 0.597 nm

D₃ vs D [6][8].

CH.05 / 10 — BASEL 1885 · LUND 1890

Hydrogen's ladder

Balmer's formula [12][13].

Rydberg 1890 [14]; Bohr [16].

THE RYDBERG FORMULA

1/λ = R_H (1/n₁² − 1/n₂²) · R_H = R∞ / (1 + mₑ/mₚ) = 109,677.58 cm⁻¹

CODATA [15]; air conversion [7].

UPPER LEVEL—

NIST [6][7]; Balmer [13].

CH.06 / 10 — HARVARD COLLEGE OBSERVATORY, 1881–1924

A quarter of a million stars, sorted by eye

Fleming: 10,351 stars [17].

Cannon: 225,300 stars [18][19][20].

Antonia Maury, 1897 [31][32].

HD counts [19]; temperatures [20].

CH.07 / 10 — CECILIA PAYNE, 1925

Mostly hydrogen

Temperature, not composition [21][22].

Almost certainly not real [21][22][23].

WHY BALMER LINES PEAK: BOLTZMANN × SAHA

Boltzmann × Saha

Boltzmann × Saha [6][25].

SURFACE TEMPERATURE—

ELECTRON PRESSURE—

Temperatures [20][30].

Payne [21]; Asplund [24].

CH.08 / 10 — HAUTE-PROVENCE, 1994–95

A star that wobbles at 59 m/s

ELODIE, 13 m/s [27].

51 Peg b [26][27][28].

HOW BIG A WOBBLE?

K = (2πG/P)^(1/3) · m sin i / (M★ + m)^(2/3) · Δλ = λ · K / c

K formula [26][27].

PLANET MASS (× sin i)—

ORBITAL PERIOD—

STAR MASS—

NASA [29][30]; IAUC [26]; Nobel [27].

CH.09 / 10 — LEGACY

From a prism to the edge of the universe

Redshift links: UNFOLD, BURST, DARK.

Blackbody link: GLOW.

A narrow slit, a prism and a lot of patience.

CH.10 / 10 — REFERENCES

SPECTRUMSPECTROSCOPY: WHAT STARLIGHT SAYS