```ts
/** Checks if value is finite number */
const isFiniteNumber = (value: number): boolean => {
  return typeof value === "number" && !isNaN(value) && Number.isFinite(value);
};

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

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