```ts
// Validate input to ensure it's a finite number that is equal to or greater than absolute zero Celsius.
function validateTemperature(celsius: number): void {
  if (typeof celsius !== "number" || !Number.isFinite(celsius)) {
    throw new Error("celsius must be a finite number");
  }
  if (celsius < -273.15) {
    throw new Error(`celsius cannot be negative or above absolute zero (${-273.15})`);
  }
}

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

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