```ts
// solution.ts

/**
 * The temperature in Fahrenheit.
 */
export function celsiusToFahrenheit(celsius: number): number {
  validateCelsius(celsius);
  return celsius * 1.8 + 32;
}

/**
 * The temperature in kelvin.
 */
export function celsiusToKelvin(celsius: number}: number {
  validateCelsius(celsius);
  return celsius + 273.15;
}

// helper functions
function validateCelsius(value: number) {
  if (typeof value !== "number" || !Number.isFinite(value)) {
    throw new Error("value must be a finite number");
  }
  if (value < -273.15) {
    throw new Error("value must be at or above absolute zero");
  }
}
```