StarCast · Night Sky Conditions
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What Is Seeing Conditions in Astronomy?

A cloudless night isn't always a sharp night. Atmospheric seeing determines how steady the air is above you. LightCast StarCast factors seeing into its night sky score for your location.

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Clear sky, blurry stars

Why Seeing Matters Even When There Are No Clouds

Cloud cover is the obvious obstacle for astrophotography. Seeing is the less obvious one. Atmospheric turbulence bends and distorts light as it passes through layers of air with different temperatures, producing the twinkling effect visible to the naked eye and blur in long exposures. You can have perfectly clear skies and still get soft, smeared stars if the atmosphere is unstable above you.

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Jet Stream Overhead
High-altitude jet stream activity is the most common cause of poor seeing. When the jet stream passes directly overhead, fast-moving air creates turbulence that blurs stars even at wide apertures. Nights when the jet stream is north or south of your location tend to have calmer, steadier air.
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Ground Heat After a Warm Day
Heat stored in the ground during the day radiates upward at night, creating convective mixing in the lowest layer of atmosphere. Nights that follow hot days often have poor low-altitude seeing for the first few hours after sunset until the ground cools.
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Humidity and Moisture Layers
High humidity and atmospheric moisture create temperature differentials between wet and dry air layers. Dry desert and high-elevation sites consistently outperform humid coastal locations for both seeing and transparency, which is why most major observatories are built in arid mountain regions.
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Elevation and Terrain
Shooting from higher elevation puts you above the densest, most turbulent part of the atmosphere. Mountain and plateau sites see a consistent improvement in both seeing and transparency over valley-floor positions. Even a few hundred feet of elevation gain makes a measurable difference.
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Seeing vs. transparency

Two Different Things That Both Affect Your Shot

Seeing and transparency are often confused. Seeing is atmospheric steadiness: it determines sharpness and star size in your images. Transparency is atmospheric clarity: it determines how faint an object you can detect. Both matter, and they don't always move together. A night after a cold front passes often has excellent transparency with poor seeing as the unsettled air stabilizes. StarCast scores both as part of its 0–100 night sky rating.

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StarCast Push Alerts
StarCast scores cloud cover, moon illumination, Bortle class, humidity, and atmospheric transparency together for any location. Push alerts notify you when a high-scoring night is forecast so you don't have to check manually every evening.
Common Questions
What is seeing in astronomy?
The steadiness of the atmosphere above your location. Turbulent air bends and distorts starlight, reducing sharpness in astrophotography even on perfectly clear nights. StarCast includes atmospheric seeing in its night sky score — available in the LightCast iOS app and at lightcastsuite.com/starcast.
What causes bad seeing?
Jet stream activity overhead, ground heat radiating after a warm day, high humidity, and rapid temperature changes between air layers. Cold, stable, dry nights at elevation consistently produce the best seeing conditions for astrophotography.
Does seeing affect Milky Way photography?
For wide-field Milky Way images, cloud cover, moon illumination, and light pollution matter more than seeing. For planetary imaging, star cluster detail, or any work requiring fine resolution, seeing is the primary image quality factor.
What is the difference between seeing and transparency?
Seeing is atmospheric steadiness, which affects sharpness. Transparency is atmospheric clarity, which affects how faint an object you can detect. Both are scored by StarCast as part of its 0–100 night sky rating for your location.
What is LightCast StarCast?
StarCast scores night sky conditions from 0 to 100 using cloud cover, moon illumination, Bortle class, humidity, atmospheric transparency, and seeing for any location. Push alerts notify you when conditions are worth the trip. Free on web at lightcastsuite.com/starcast, with push notifications in the LightCast iOS app. $2.99/month after a 7-day free trial.
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Know if tonight's air is steady enough to shoot.

Atmospheric seeing · Transparency · Cloud cover · Moon illumination
Bortle class · Push notifications · 0–100 night sky score

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