script.js

const c = 299792; // velocidade da luz em km/s
const button = document.getElementById("calc");
const resultBox = document.getElementById("result");
const star = document.getElementById("star");

// fundo de estrelas
const starsBg = document.getElementById("stars");
for (let i = 0; i < 150; i++) {
    const s = document.createElement("span");
    s.style.left = Math.random() * 100 + "%";
    s.style.top = Math.random() * 100 + "%";
    s.style.animationDelay = Math.random() * 3 + "s";
    s.style.opacity = Math.random();
    starsBg.appendChild(s);
}

button.addEventListener("click", () => {
    const H0 = parseFloat(document.getElementById("hubble").value);
    const d = parseFloat(document.getElementById("distance").value);

    if (isNaN(H0) || isNaN(d)) {
        resultBox.textContent = "Por favor, insira valores válidos!";
        return;
    }

    const v = H0 * d;
    const z = v / c;

    resultBox.innerHTML = `
        Velocidade: ${v.toFixed(2)} km/s <br>
        Redshift: ${z.toFixed(5)}
    `;

    // cor redshift / blueshift
    let color;

    if (z < 0) {
        const intensity = Math.min(255, 255 * Math.abs(z) * 50 + 100);
        color = `rgb(${100 - Math.abs(z) * 200}, ${120 - Math.abs(z) * 100}, ${intensity})`;
    } else {
        const red = Math.min(255, 200 + z * 90000);
        const blue = Math.max(0, 255 - z * 100000);
        color = `rgb(${red}, ${150 - z * 20000}, ${blue})`;
    }

    star.style.background = `radial-gradient(circle at center, #fff, ${color})`;
    star.style.boxShadow = `0 0 ${40 + Math.abs(z) * 400}px ${color}`;
    star.style.animationDuration = `${2 - Math.min(Math.abs(z) * 8, 1.5)}s`;
});