```ts
/**
 * The temperature in degrees Fahrenheit.
 */
export function celsiusToFahrenheit(celsius: number): number {
  return validateCelsius(celsius) * 1.8 + 32;
}

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

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