```ts

function isFiniteAndPositive(celsius: number): boolean {
  return typeof celsius === "number" && Number.isFinite(celsius) && celsius >= -273.15;
}

export function celsiusToFahrenheit(celsius: number): number {
  if (!isFiniteAndPositive(celsius)) {
    throw new Error("celsius must be a finite and positive number");
  }
  return celsius * 1.8 + 32;
}

export function celsiusToKelvin(celsius: number): number {
  if (!isFiniteAndPositive(celsius)) {
    throw new Error("celsius must be a finite and positive number");
  }
  return celsius + 273.15;
}
```