```ts
/** The temperature in degrees Fahrenheit. */
export function celsiusToFahrenheit(celsius: number): number {
  if (!isFiniteNumber(celsius)) {
    throw new Error("celsius must be a finite number");
  }
  return celsius * 1.8 + 32;
}

/** The temperature in kelvin. */
export function celsiusToKelvin(celsius: number): number {
  if (!isFiniteNumber(celsius)) {
    throw new Error("celsius must be a finite number");
  }
  return celsius + 273.15;
}

/**
 * Helper function to validate the input is a finite number.
 */
function isFiniteNumber(input: number): boolean {
  return typeof input === "number" && Number.isFinite(input) && input >= -273.15;
}
```