Satellite Visibility Calculator
Calculate when and where to look for ISS and satellite passes from your location. Enter values for instant results with step-by-step formulas.
Formula
T = 2 * pi * sqrt(a^3 / mu) | footprint = R_earth * arccos(R_earth * cos(elev) / (R_earth + h))
Where T is orbital period, a is semi-major axis (Earth radius + altitude), mu is Earth gravitational parameter (398600.4 km^3/s^2), footprint is the visibility radius on Earth surface, R_earth is 6371 km, h is orbital altitude, and elev is minimum elevation angle.
Worked Examples
Example 1: ISS Pass from New York City
Problem: Calculate visibility parameters for the ISS (408 km altitude, 51.6 degree inclination) from New York City (40.71 N, 74.01 W) with a 10-degree minimum elevation.
Solution: Orbital period = 2 * pi * sqrt((6371+408)^3 / 398600.4) = 5,554 seconds = 92.6 minutes\nOrbits per day = 86400 / 5554 = 15.6\nFootprint radius at 10 deg elevation = approximately 1,800 km\nMax latitude visible = 51.6 + footprint angle = well above 40.71 N, so ISS is visible\nPass duration = footprint diameter / ground speed = approximately 6.1 minutes\nEstimated visible passes per day = approximately 2-4 during twilight
Result: Orbital Period: 92.6 min | Passes/Day: ~3 | Pass Duration: ~6 min | Max Elevation: 90 degrees
Example 2: Low Earth Orbit Spy Satellite
Problem: A reconnaissance satellite orbits at 250 km altitude with 97-degree sun-synchronous inclination. Calculate visibility from London (51.5 N).
Solution: Orbital period = 2 * pi * sqrt((6371+250)^3 / 398600.4) = 5,330 seconds = 88.8 minutes\nOrbits per day = 86400 / 5330 = 16.2\nLower altitude means smaller footprint but faster passes\nAt 97 deg inclination, visible from all latitudes up to ~97 + footprint angle\nShorter pass duration due to lower altitude and faster ground speed\nDimmer than ISS due to much smaller size (magnitude 3-5)
Result: Orbital Period: 88.8 min | Passes/Day: ~4 | Pass Duration: ~4 min | Sun-synchronous: same local time daily
Frequently Asked Questions
How does the Satellite Visibility Calculator determine when I can see a satellite?
The calculator uses orbital mechanics principles to determine satellite visibility from your location. It considers the satellite orbital altitude, inclination angle, and your geographic coordinates to compute the ground track and footprint radius. A satellite is visible when it passes within your line of sight above the minimum elevation angle you specify. The calculator also factors in the geometry between the Earth radius, orbital radius, and observer position to determine pass duration and maximum elevation. Visibility requires the satellite to be in sunlight while the observer is in darkness or twilight, which is why most visible passes occur shortly after sunset or before sunrise.
What is orbital inclination and why does it matter for visibility?
Orbital inclination is the angle between the satellite orbital plane and the Earth equatorial plane, measured in degrees. The ISS has an inclination of 51.6 degrees, meaning it never passes directly over latitudes higher than 51.6 degrees north or south. This is critical for visibility because observers at latitudes beyond the inclination plus the visibility footprint angle will never see the satellite. Polar orbiting satellites with inclinations near 90 degrees can be seen from almost anywhere on Earth. Sun-synchronous satellites at about 98 degrees inclination pass over every point on Earth but always at the same local solar time, making them predictable targets for observation.
How accurate are satellite pass predictions from Satellite Visibility Calculator?
Satellite Visibility Calculator provides estimates based on orbital mechanics fundamentals including Kepler laws and geometric visibility constraints. The results give you approximate pass frequency, duration, and maximum elevation for planning purposes. For precise pass times accurate to the second, dedicated tracking services like Heavens-Above or NASA Spot the Station use regularly updated two-line element sets that account for atmospheric drag, orbital maneuvers, and other perturbations. Our calculator is best used for understanding general visibility patterns, comparing different satellite orbits, and learning how orbital parameters affect what you can see. Real satellite orbits decay over time due to atmospheric drag, requiring periodic reboosts, which means exact predictions are only accurate days in advance.
What is a satellite footprint and how does it relate to visibility?
A satellite footprint is the circular area on the Earth surface from which the satellite can be seen above a given minimum elevation angle at any instant. For a satellite at 408 kilometers altitude with a 10-degree minimum elevation, the footprint radius is roughly 1,800 kilometers. As the satellite moves along its orbit, this footprint sweeps a long swath across the Earth surface. If your location falls within this swath, you will experience a visible pass. The footprint size depends on altitude and minimum elevation angle. Higher satellites have larger footprints and can be seen from a wider area, but they appear dimmer because they are farther away. The footprint concept helps explain why two observers a few hundred kilometers apart may see the same pass at slightly different times and elevations.
How does latitude affect the number of satellite passes I can see?
Your latitude significantly impacts how many passes of a given satellite you can observe. For satellites with moderate inclinations like the ISS at 51.6 degrees, observers near the maximum latitude see fewer passes because the satellite ground track only clips the edge of their visibility zone. Observers at lower latitudes within the inclination range see more frequent passes with higher maximum elevations. Equatorial observers can see satellites of almost any inclination because all orbits cross the equator. Polar observers above 60 degrees latitude miss many satellites entirely but have excellent access to polar-orbiting satellites. The combination of your latitude, the satellite inclination, and the footprint size determines your total observable passes per day, which typically ranges from one to six for the ISS.
How are satellite orbits classified?
Low Earth Orbit (LEO) is 200-2,000 km altitude with 90-minute periods and is used for the ISS and imaging satellites. Medium Earth Orbit (MEO) at 2,000-35,786 km is used for GPS. Geostationary Orbit (GEO) at 35,786 km matches Earth's rotation for communication satellites. Sun-synchronous orbits pass over areas at the same local time.