```ts
export function celsiusToFahrenheit(celsius: number): number {
  return _convertCelsiusTo(celsius, 1.8 + 32);
}

export function celsiusToKelvin(celsius: number): number {
  return _convertCelsiusTo(celsius, 273.15);
}

function _convertCelsiusTo(celsius: number, scale: 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 * scale;
}
```