```ts
/** Checks if the input value must be a finite number */
export function isFiniteNumber(value: any): boolean {
  return typeof value === "number" && !isNaN(Number(value));
}

/** The temperature in degrees Fahrenheit. */
export function celsiusToFahrenheit(celsius: number): number {
  isFiniteNumber(celsius);
  if (celsius < -273.15) {
    throw new Error("celsius must be at or above absolute zero");
  }
  return celsius * 1.8 + 32;
}

/** The temperature in kelvin. */
export function celsiusToKelvin(celsius: number): number {
  isFiniteNumber(celsius);
  if (celsius < -273.15) {
    throw new Error("celsius must be at or above absolute zero");
  }
  return celsius + 273.15;
}
```