Use 600 lines/mm grating from Peter to record the region around the Oxygen line during re-entry. This is at 777nm. The formula for the angular offset A between zeroth and first-order spectrum at wavelength W is below. On-line grating angle calculator is here. 110nm FOV on PC164C chip width, est by PJ at SETI. 25.6 nm per degree on the sky
A = sin-1(600mm-1 x W(mm)).
A = sin-1(600 x 777.4x10-6) = 27.80 degrees for 777nm Oxygen, and 28.30 deg for 790nm optimum for getting both O I's and both N I triplets
A = 20.70 deg for Sodium D at 589nm
A = 23.2 deg for H-alpha at 656nm
For practice, consider using Mercury Vapor street lights or Low or High Pressure Sodium street lights...
LP Sodium, essentially a single line at 589.0nm of the Sodium D doublet |
Visual of spectrum of HP sodium lamp. The sharp line at the green/yellow boundary is the 589 nm Sodium D line, broadened by high pressure |
Leonid spectrum in near IR, with my setup's FOV indicated. Wavelengths of O I 845nm, middle of N I triplet at 825nm, O I at 777nm, and middle of N Itriplet at 745nm indicated. (from Jenniskens etal 2004) |
Spectrum of HP Sodium street lamp |
Star pairs at relevant angular offsets are below. Note that these pairs will be at different position angle on the sky and therefore will give different orientation to the direction of dispersion. You want the direction of dispersion to ideally be perpendicular to the vector between capsule and spacecraft.
Java Applet for Angle Between Two Stars (note 25.6 nm per degree on the sky, and 110 nm = width of FOV). On-line grating angle calculator
Oxygen I (777nm) Star Pairs
Antares: RA=16.49h Dec=-26.432 and Eta Centauri: RA=14.591666h Dec=-42.15777 gives sep=28.08deg
Sigma Sco: RA=16.353h Dec=-25.592777 and Eps Sagittarii RA=18.403h Dec=-34.38466 gives sep=27.92deg
Spica: RA=13.42h Dec=-11.161388 and Beta Librae: RA=15.28333 Dec=-9.38305 gives sep=27.55deg
Alpha Ser V=2.7 K2 RA=15.73777h Dec=6.425555 and delta Boo V=3.5 RA=15.258333 Dec=33.314722 gives sep=27.705deg
Alpha Ser V=2.7 K2 RA=15.73777h Dec=6.425555 and Omega1 Sco V=4 RA=16.113333h Dec=-20.6691666 gives sep=27.654deg
Alpha Ser V=2.7 K2 RA=15.73777h Dec=6.425555 and Alpha Oph RA=17.58222 Dec=12.56000 gives sep=27.95deg
Denebola V=2.2 A3 RA=11.817766 Dec=14.5719444 and Cor Caroli V=2.8 RA=12.933888 Dec=38.318333 gives sep=27.975deg
Saturn V=1.2 RA=11.94 Dec=2.9835 and Beta (foot) Corvus (V=2.7 G5) RA=12.57305 Dec=-23.39666 gives sep=27.96deg and Perp to Path
Arcturus V=0.2 RA=14.261111 Dec=19.1825 and Mu Vir V=3.9 F2 RA=14.717777 Dec=-5.658333 gives sep=25.74. Need 2.56 deg more. That's 9.3% more distance than the distance and dir from 109 Vir to Mu Vir
Sodium D lines at 589nm Angle=20.7 deg radius, 41.4deg diameter for C2A
Denebola V=2.2 A3 RA=11.817766 Dec=14.5719444 and Gamma Vir (Porrima) V=2.8 RA=12.6944433 Dec=-01.449444 gives sep=20.644deg
Alpha Ser V=2.7 K2 RA=15.73777h Dec=6.425555 and Alpha CorBor RA=15.57805 Dec=26.714722 gives sep=20.417 deg
H-Alpha line at 656nm, angle=23.2 deg radius or 46.4 deg diameter for C2A
Spica RA=13.42 Dec=-11.1613888 and Epsilon Virginis (her hand) V=3 RA=13.0363888 Dec=10.9591666 gives sep=22.85 deg
delta Oph V=3 RA=16.239166 Dec=-03.694444 and gamma Herculis V=3.7 RA=16.3652777 Dec=19.1530555 gives sep=22.92 deg
theta Leonis V=3.3 RA=11.237222 Dec=15.42944 and Omicron Leonis V=3.7 RA=9.685833 Dec=9.89222 gives sep= 23.353deg
Early Eve for proper 180 orientation of grating: recording cam at Procyon and tracking cam on Venus. Must get both angle diff and grating rotation on same pair, so essential that at least one of our stars be bright enough to produce a spectrum.
