```ts
// import { assert } from "assert";

/** The temperature in degrees Fahrenheit. */
export function celsiusToFahrenheit(celsius: number): number {
  const validate = _validateCelsius(celsius);
  return validate * 1.8 + 32;
}

/** The temperature in kelvin. */
export function celsiusToKelvin(celsius: number): number {
  const validate = _validateCelsius(celsius);
  return validate + 273.15;
}

function _validateCelsius(value: unknown): number {
  if (typeof value !== "number" || !Number.isFinite(value)) {
    throw new Error("celsius must be a finite number");
  }
  if (value < -273.15) {
    throw new Error("celsius must be at or above absolute zero");
  }
  return value;
}
```