```ts
/**
 * Validates whether the given value is a finite number and greater than or equal to absolute zero.
 * @param value The value to validate.
 * @throws Error if the value is not a finite number or less than absolute zero.
 */
function validateCelsiusTemperature(value: number): void {
  if (typeof value !== "number" || !Number.isFinite(value)) {
    throw new Error("celsius must be a finite number");
  }
  if (value < -273.15) {
    throw new Error("celsius must be at or above absolute zero");
  }
}

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

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