```ts
import { Number } from "https://deno.land/std@0.108.0/types/mod.ts";

function validateTemperatureValue(value: number): void {
  if (typeof value !== "number" || !Number.isFinite(value)) {
    throw new Error("must be a finite number");
  }
}

/** The temperature in degrees Fahrenheit. */
export function celsiusToFahrenheit(celsius: number): number {
  validateTemperatureValue(celsius);
  if (celsius < -273.15) {
    throw new Error("at or above absolute zero");
  }
  return celsius * 1.8 + 32;
}

/** The temperature in kelvin. */
export function celsiusToKelvin(celsius: number): number {
  validateTemperatureValue(celsius);
  if (celsius < -273.15) {
    throw new Error("at or above absolute zero");
  }
  return celsius + 273.15;
}
```