```typescript
/** Checks if Celsius must be a finite number */
function validateCelsius(number: any): boolean {
  return typeof number === "number" && !isNaN(number);
}

export function celsiusToFahrenheit(celsius: number): number {
  validateCelsius(celsius);
  if (celsius < -273.15) {
    throw new Error("celsius must be at or above absolute zero");
  }
  return celsius * 1.8 + 32;
}

export function celsiusToKelvin(celsius: number): number {
  validateCelsius(celsius);
  if (celsius < -273.15) {
    throw new Error("celsius must be at or above absolute zero");
  }
  return celsius + 273.15;
}
```