Sky Clarity
๐ Forecast Location
What Does My Sky Clarity Grade Mean?
Every grade is a composite of three scores โ Transparency, Seeing, and Darkness. The right column shows exactly what targets are realistically within reach at each level.
- APristine Skies Go NowBest Targets Faint nebulae, distant galaxies, Milky Way dust lanes, zodiacal light. Ideal for all deep-sky astrophotography. Don't waste this night indoors.
- BExcellent Viewing Go ObserveBest Targets Open clusters, Andromeda Galaxy, bright nebulae. The sweet spot for wide-field binocular sessions and lunar photography on crescent nights.
- CFair Conditions Partial ViewBest Targets Bright planets like Jupiter and Saturn, the Moon's craters and mountain ranges. Deep-sky targets will be washed out entirely.
- DPoor Conditions Planets OnlyBest Targets Venus and Jupiter only. Save your telescope and use the time to plan your next session around the 2026 astronomy calendar.
- FTotal Washout Stay InsideBest Targets None. Observation is impossible. Clean your optics and check when the next new moon falls for your best upcoming window.
The Physics of Sky Clarity
For an astronomer, a "clear sky" isn't simply the absence of rain. It is a complex calculation of light scattering, air stability, moisture content, and lunar interference. Our tracker analyzes all four in real time โ cross-referencing live weather data against the moon phase today โ to tell you whether the sky is truly dark, or merely cloudless.
High humidity and aerosols scatter city light, creating a haze that erases deep-sky objects entirely. A forecast of 0% cloud cover can still produce a C-grade if humidity climbs above 80%.
Transparency is why dark sky parks exist โ even a cloudless suburban sky carries a permanent haze penalty that no overnight forecast can fix.
The Moon is the most powerful natural source of light pollution. During a Full Moon the sky is never truly dark regardless of weather. A Supermoon pushes up to 30% brighter still.
Crucially, we factor in the Moon's altitude โ a Full Moon sitting 5ยฐ above the horizon contributes almost no glare. A Full Moon at 60ยฐ overhead is a session-killer.
Seeing describes air stability, not transparency. Turbulent air causes stars to twinkle rapidly and telescope images to blur โ this is why stars shimmer more on cold nights despite the sky appearing perfectly clear.
A calm, mild night frequently outperforms a clear, freezing one for planetary detail and high-magnification work.
High humidity doesn't just haze the sky โ at the dew point it condenses directly onto telescope optics, fogging your eyepiece mid-session.
Humidity above 85% is a practical session-ender even when the sky looks passable. A dry night is always the superior choice for any serious observation.
The Bortle Scale & Your Permanent Sky Quality
Our grade measures tonight's conditions โ but your baseline sky quality is fixed by where you live. The Bortle Dark-Sky Scale ranks light pollution from 1 (total darkness) to 9 (inner-city glare). Think of the clarity grade as a nightly multiplier on top of your permanent Bortle baseline. A Grade A night in a Bortle 8 city will never match a Grade C night in a remote desert.
The practical implication: if you live in suburbs (Bortle 6โ7), even a Grade A score won't reveal the faint Milky Way structure that rural observers take for granted. For serious deep-sky work, a two-hour drive to dark skies on a Grade B night will outperform a Grade A from your backyard every time.
| Class | Location | Limiting Magnitude | What You Can See |
|---|---|---|---|
| 1โ2 | Remote wilderness | 7.6โ8.0 | Zodiacal light, airglow, M33 easily naked eye, shadow cast by Milky Way |
| 3โ4 | Rural / semi-rural | 6.6โ7.5 | Milky Way in full detail, most Messier objects visible without optical aid |
| 5โ6 | Suburban outskirts | 5.6โ6.5 | Milky Way faint, bright clusters and nebulae visible, most Messier objects need binoculars |
| 7โ8 | Suburbs / small city | 4.5โ5.5 | Only bright constellations, Orion Nebula just visible, Milky Way invisible |
| 9 | Inner city | <4.5 | Planets, Moon, and the brightest 50 stars only |
Matching Your Equipment to the Conditions
Your Bortle class sets the ceiling. Your sky grade sets the floor for tonight. The biggest mistake beginners make is dragging out a telescope on a Grade D night and blaming the equipment when nothing looks sharp. Use this table to make a go/no-go call before you spend an hour cooling down your optics in the cold.
| Equipment | Minimum Grade | Realistic Targets by Condition |
|---|---|---|
| Naked Eye No equipment needed | C or better | A Milky Way dust lanes, zodiacal light, faint meteors | B Andromeda Galaxy, star clusters | C Major constellations and bright planets only |
| Binoculars 7ร50 or 10ร50 recommended | B or better | AโB Open clusters, Andromeda core, faint nebulae, detailed lunar craters on crescent nights |
| Small Telescope 70โ130mm aperture | B deep sky ยท C planets | AโB Globular clusters, planetary nebulae, galaxy cores | C Jupiter's cloud bands and moons, Saturn's rings, Copernicus crater |
| Large Telescope 200mm+ aperture | A for faint targets | A Faint galaxy clusters, nebula detail, close double stars | B Bright Messier objects, planetary disc detail | C Lunar craters only |
| Astrophotography Camera + tracking mount | A only | Long exposures mercilessly expose every trace of light pollution and atmospheric turbulence. Only shoot on Grade A nights with humidity below 60%. |
Tools to Go Deeper
The most useful pages on this site for planning a complete stargazing session.
What's Your Sky Doing Right Now?
Enter your city in the tracker at the top of the page. Cloud cover, lunar illumination, seeing, and humidity โ combined into one instant grade.
โ Check My Sky Grade