During my graduate research I needed to obtain high‑resolution spectra of variable stars.

I had to select and operate a spectrograph to capture the stellar absorption lines accurately.

I explained that a spectrograph disperses incoming light using a diffraction grating onto a detector, allowing us to record intensity versus wavelength. I described the slit, collimator, grating, camera optics, and CCD, and highlighted calibration steps such as flat‑fielding and wavelength standards.

The resulting spectra revealed precise radial velocity changes, enabling us to model the star’s pulsation period with 2% uncertainty.

Before a night of deep‑field imaging at the observatory, the CCD camera showed inconsistent bias levels.

I needed to perform a full calibration sequence to ensure photometric accuracy.

I took a series of bias frames, dark frames matching the exposure time and temperature, and twilight flat fields across all filters. I then applied these corrections using standard reduction pipelines, verifying the uniformity of the final images with standard stars.

The calibrated images achieved a photometric precision of 0.01 mag, meeting the project’s requirements.

In a survey of high‑z galaxies I needed to measure their cosmological redshifts.

Identify spectral features and calculate the shift relative to rest wavelengths.

I extracted the 1‑D spectrum, identified prominent emission lines (e.g., Lyα, [O II]), measured their observed wavelengths, and applied z = (λ_obs‑λ_rest)/λ_rest. I then cross‑checked with template fitting to account for line blending and instrumental resolution.

The derived redshifts had uncertainties <0.001, allowing accurate placement of galaxies on the Hubble diagram.