Stargazing is the one outdoor pursuit where a single factor overwhelmingly decides the night, and the score reflects that: cloud cover is weighted more heavily than anything else. It does not matter how dark your site is or how good your telescope is if a blanket of cloud sits between you and the sky. Even thin, high cloud that is barely noticeable in daylight can wash out fainter stars and ruin the view of deep-sky objects. The score therefore rewards genuinely clear skies and falls steeply as cloud increases, because for astronomy, a clear sky is not merely preferable, it is the entire foundation of a good night.
Beyond raw cloud cover, two subtler factors shape the quality of a clear night, and the score accounts for them. Transparency describes how clean and dry the air is: humid, hazy air scatters light and dims faint objects even under an apparently cloudless sky, which is why the score favours lower humidity. Astronomers also talk about seeing, which is the steadiness of the atmosphere, since turbulent air makes stars twinkle and blurs fine detail through a telescope. Calm, stable conditions give the sharpest views, so the score treats a still night kindly. Together these mean that not all clear skies are equal, and a dry, calm, transparent night is worth far more than a humid, turbulent one.
One crucial ingredient for stargazing is not weather at all but the moon, and it deserves a mention the score cannot fully capture. A bright full moon floods the sky with light and washes out all but the brightest stars, making the nights around full moon poor for observing faint objects, while the dark nights around new moon are prized by astronomers. For the best deep-sky viewing, combine a high weather score here with a date near new moon. Our companion moon phase page shows exactly where in the cycle tonight falls, so the complete picture for a great night is a clear, dry, calm sky on this page paired with a dark, moonless sky from the lunar calendar.
When the score is high, a little preparation transforms the experience. Get away from city lights if you can, since light pollution rivals cloud as the enemy of a dark sky, and even a short drive to darker surroundings dramatically increases how much you can see. Give your eyes at least twenty minutes to adapt to the dark, avoiding white light, and let your telescope or binoculars cool to the outside temperature to avoid distorted views. Dress far more warmly than you think you need to, because standing still under a clear, calm sky, exactly the conditions the score rewards, gets cold quickly. With a high score, a dark moonless sky and a little patience, even modest equipment reveals a breathtaking amount.