A live tracker shows the ISS at 418 km, a Starlink satellite at 550 km, and a weather satellite at 35,786 km. Those numbers look simple, but knowing how to read orbital altitude turns them into a real-time picture of speed, visibility, coverage, and what you can expect to see from your backyard. Altitude is the satellite’s height above Earth, not its height above your local horizon – and that distinction is mission-critical.
| Orbit example | Typical orbital altitude (km) | Approx. period (minutes) | Approx. speed (km/h) |
|---|---|---|---|
| International Space Station | 370-420 km | 90-93 min | 27,600 km/h |
| Typical operational Starlink satellite | About 550 km | 96 min | 27,000 km/h |
| GPS navigation satellite | 20,200 km | 718 min | 14,000 km/h |
| Geostationary weather or communications satellite | 35,786 km | 1,436 min | 11,100 km/h |
What orbital altitude actually measures
Orbital altitude is normally reported in kilometers above a reference Earth surface, usually a mathematical model called an ellipsoid rather than the mountain, ocean, or city directly beneath the spacecraft. A tracker value of 400 km means the spacecraft is roughly 400 km above Earth’s reference surface at that instant.
That is very different from elevation, the angle between the satellite and your local horizon. Elevation is measured in degrees: 0 degrees is on the horizon and 90 degrees is directly overhead. An ISS tracker can report an orbital altitude near 400 km while the station is only 8 degrees above your horizon, partly hidden by buildings, trees, haze, and the thicker lower atmosphere.
For observing, elevation usually matters more than orbital altitude. For understanding the spacecraft’s mission and motion, altitude is the key number.
How to read orbital altitude on a tracker
Start by finding the unit. Most consumer trackers display kilometers, while some US-focused displays offer miles. One kilometer equals 0.621 miles, so an ISS altitude of 400 km is about 249 miles. Do not confuse that reading with distance from you. A spacecraft directly overhead at 400 km is roughly 400 km away, but the same spacecraft near the horizon can be more than 1,500 km away along your line of sight.
Next, check whether the value is labeled current altitude, perigee, apogee, or average altitude. Current altitude is the live or calculated value at one moment. Perigee is the lowest point of an orbit, while apogee is the highest. A satellite in a nearly circular orbit has similar perigee and apogee values. A satellite on a stretched, elliptical path can have dramatically different values.
A tracker may show an orbit such as 380 km x 420 km. Read that as approximately 380 km at perigee and 420 km at apogee. The object is not constantly changing engines or climbing on purpose. It is coasting through an ellipse, moving fastest near its low point and slowest near its high point.
Finally, read the data timestamp. Satellite trackers project positions from orbital elements, often with an epoch listed in UTC. If an element set is marked 2026-08-27 00:00 UTC, it describes the orbit at that reference time and is propagated forward from there. Fresh data improves predictions, especially for low-orbit spacecraft affected by atmospheric drag and occasional maneuvers.
The altitude labels that matter
Low Earth orbit, or LEO, generally extends from roughly 160 km to 2,000 km. This is the fast-moving zone for the ISS, Hubble Space Telescope, many Earth-observation missions, and large satellite constellations. Objects in LEO circle Earth in about 90 to 130 minutes, which is why they race across the sky during a visible pass.
Medium Earth orbit, or MEO, sits between about 2,000 km and 35,786 km. GPS satellites operate around 20,200 km, high enough to cover wide areas of Earth but far below geostationary orbit. They take almost 12 hours to complete an orbit.
Geostationary orbit, or GEO, is the special ring at 35,786 km above the equator. At that altitude, a satellite’s orbital period matches Earth’s sidereal rotation: 23 hours, 56 minutes, and 4 seconds. To an observer, it appears fixed over one longitude. That is why a dish antenna can point at one location in the southern sky instead of tracking a moving satellite.
Why a few kilometers can matter
At ISS altitude, Earth is not perfectly isolated from the spacecraft. The extreme upper atmosphere creates drag, gradually lowering the orbit. A change of 10 km is minor for a casual skywatcher, but it is meaningful to flight planners because denser air at lower altitudes increases drag. Periodic reboosts raise the station’s orbit to maintain safe operating margins.
Altitude also influences how long a satellite stays in view. Lower spacecraft move faster against the stars and typically cross the sky in 3 to 7 minutes. Higher spacecraft move more slowly, but distance makes them dimmer. That trade-off explains why a bright ISS pass at 400 km can be easy to spot, while a GPS satellite at 20,200 km is not a naked-eye target.
Brightness is never an altitude-only prediction. Satellite size, surface reflectivity, orientation, your local light pollution, the Moon, and whether the spacecraft remains sunlit all matter. A 550 km Starlink satellite can be visible shortly after sunset or before sunrise, while another at the same altitude may be too faint to notice because its attitude or illumination geometry is different.
Pair altitude with these live-tracker fields
Altitude becomes far more useful when read beside a few other fields. Look for ground speed, which confirms why a LEO object can cover roughly 27,000 km every hour. Check inclination, the angle of the orbital plane relative to Earth’s equator. The ISS inclination is 51.6 degrees, so it can pass over cities from about 51.6 degrees north latitude to 51.6 degrees south latitude, but never directly over Alaska’s North Slope or southern Patagonia.
Also check maximum elevation and pass time. For a practical viewing plan, a pass peaking above 30 degrees is often worth stepping outside for, while 60 degrees or more can be spectacular if the spacecraft is sunlit. Use the listed local time carefully: many mission and orbital data displays default to UTC, which is 4 hours ahead of Eastern Daylight Time and 7 hours ahead of Pacific Daylight Time.
The direction field tells you where to face. A pass beginning in the northwest, peaking at 68 degrees elevation, and ending in the southeast is an observation route, not just a collection of numbers. Give yourself a clear view in the starting direction about two minutes early.
A quick orbital-period reality check
If a tracker reports a circular-orbit altitude, you can make a useful sanity check. Orbital period grows with altitude. Near 400 km, an orbit takes about 92 minutes. Near 550 km, it takes about 96 minutes. At 35,786 km, it takes one sidereal day.
The physics behind that result is straightforward: gravity is weaker farther from Earth, so a satellite travels more slowly and covers a much larger orbital path. A spacecraft does not hover because it is high. It remains in orbit because its sideways speed continuously carries it around Earth as gravity pulls it inward.
That is also why altitude alone cannot tell you where the object will appear next. You need the full orbit, Earth’s rotation, and your location. A live tracker handles those calculations, then translates them into the fields you actually need: time, direction, elevation, range, and brightness estimate.
The next time a tracker flashes an altitude number, treat it as the start of the mission picture. Pair it with elevation and illumination, then step outside when the geometry lines up. SpaceInformer-style live data makes the orbit visible, but your horizon is where the pass becomes real.