```typescript
/** The temperature in degrees Fahrenheit. */
export function celsiusToFahrenheit(celsius: number): number {
  return validateTemperature(celsius, (t) => t * 1.8 + 32);
}

/** The temperature in kelvin. */
export function celsiusToKelvin(celsius: number): number {
  return validateTemperature(celsius, (t) => t + 273.15);
}

function validateTemperature(celsius: number, conversionFunction: (t: number) => number): number {
  if (typeof celsius !== "number" || !Number.isFinite(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 conversionFunction(celsius);
}
```