Learn space: every question, answered with live data
Every space explainer, definition, live-data page and tracker on Cosmik, indexed in one place — so any answer is at most two clicks away.
This is the Cosmik encyclopedia: a single index of everything we explain about space, from what a star is to where Artemis II is right now. Every explainer, glossary definition, live-data page and tracker below is at most two clicks away — and the answers are backed by real-time positions and counts, not static text.
Questions & explainers
Plain-language answers to the big questions, each linking straight to the live 3D view.
- What is a star?A star is a giant sphere of plasma held together by gravity and powered by nuclear fusion. How stars ignite, live for millions to trillions of years, and die — explained simply.
- What is the Deep Space Network?The Deep Space Network (DSN) is NASA's system of giant radio antennas in California, Spain and Australia that communicates with every deep-space probe — including Voyager 1, 25 billion km away.
- What is an orbit?An orbit is a continuous fall around a planet: satellites move sideways so fast (7.7 km/s in LEO) that they keep missing the Earth. LEO, MEO, GEO and how trackers predict positions, explained.
- What is the ISS?The International Space Station is a football-field-sized laboratory orbiting 400 km up at 28,000 km/h, crewed continuously since November 2000. What it does and how to spot it with your eyes.
- What is a satellite constellation?A satellite constellation is a coordinated fleet working as one system: Starlink's 10,000+ satellites for internet, GPS's 31 for navigation. How they work and why they're transforming the sky.
- How do rocket launches work?Why launches have exact windows, why they scrub, and what happens from T-0 to orbit — the 8-minute journey from the pad to 28,000 km/h, explained simply.
- What happens when a satellite falls?Dead satellites don't stay up forever: atmospheric drag pulls them down until they re-enter at 28,000 km/h and mostly burn up as artificial meteors. When they fall and what survives.
- What is space debris?Over 36,000 tracked debris objects and an estimated 130 million fragments too small to track orbit Earth at bullet speeds. Where junk comes from, conjunction warnings, and Kessler syndrome.
- Why do satellites blink at night?Satellites don't carry visible lights — the blinking is sunlight glinting off a tumbling object. How to read the flashes, tell satellites from planes, and catch a flare.
- Can you see satellites during the day?With the naked eye, almost never — the sky outshines them. The exceptions (ISS in twilight, fresh Starlink trains, reentry fireballs) and when satellite-spotting actually works.
- How do satellites look in the sky?A satellite looks like a steady, non-blinking star gliding smoothly across the sky in 2–5 minutes. How to tell a satellite from a plane, a star or a meteor at a glance.
- Can you see satellites with a telescope?Yes, but satellites move fast — the trick is your naked eye finds them and the telescope reveals detail. How to catch the ISS, Starlink and more through a scope.
- Can you see the northern lights when it's cloudy?No — the aurora forms about 100 km up, far above the clouds, so an overcast sky blocks it completely. Why clouds hide it and what to do on a cloudy night.
- What is the Kp index?The Kp index is a 0–9 scale of how disturbed Earth's magnetic field is right now. What Kp means, how it maps to G-class storms, and how high it must be to see aurora.
Glossary
Every space term in one-line definitions. See the full space glossary, or jump straight to a term.
Orbits & orbital mechanics
- LEO (low Earth orbit) — Low Earth orbit (LEO) is the region of space from about 160 to 2,000 km above Earth's surface, where satellites circle the planet in roughly 90 minutes.
- MEO (medium Earth orbit) — Medium Earth orbit (MEO) is the band from about 2,000 km up to the geostationary altitude of 35,786 km, best known as the home of navigation satellites.
- GEO (geostationary Earth orbit) — Geostationary orbit (GEO) is the circular orbit 35,786 km above the equator where a satellite's period exactly matches Earth's rotation, so it appears fixed over one spot.
- HEO (highly elliptical orbit) — A highly elliptical orbit (HEO) is a stretched, egg-shaped orbit with a low perigee and a very high apogee, letting a satellite linger for hours over one hemisphere.
- Sun-synchronous orbit (SSO) — A sun-synchronous orbit (SSO) is a near-polar low Earth orbit tuned so the satellite passes over every location at the same local solar time on each visit.
- Geostationary satellite — A geostationary satellite orbits 35,786 km above the equator in step with Earth's rotation, so from the ground it appears to hang motionless in the sky.
- Apogee — Apogee is the point in an orbit around Earth where the satellite is farthest from the planet.
- Perigee — Perigee is the point in an orbit around Earth where the satellite is closest to the planet.
- Orbital inclination — Orbital inclination is the angle between a satellite's orbital plane and Earth's equator, measured in degrees.
- RAAN & the ascending node — The ascending node is where a satellite crosses the equator heading north; RAAN (right ascension of the ascending node) is the angle that fixes that crossing point in space.
- Lagrange point — A Lagrange point is one of five positions in a two-body system, such as the Sun and Earth, where gravity and orbital motion balance so a spacecraft can hold station with little fuel.
- Orbital period — The orbital period is the time a satellite takes to complete one full orbit, set almost entirely by its altitude.
- Ground track — A ground track is the path traced on Earth's surface directly beneath a satellite as it orbits.
- Satellite constellation — A satellite constellation is a group of satellites working together as one system to give continuous or global coverage that a single satellite cannot.
Launch & reentry
- Delta-v (Δv) — Delta-v (Δv) is the change in velocity a spacecraft must produce to perform a manoeuvre — launching, changing orbit or landing — and it is the basic currency of orbital mechanics.
- Max-Q — Max-Q is the moment during a rocket launch when aerodynamic pressure on the vehicle is at its greatest, usually about a minute after liftoff.
- Atmospheric reentry — Atmospheric reentry is the return of a spacecraft or piece of debris into Earth's atmosphere, where friction and compression heat it to thousands of degrees.
Tracking & data
- GNSS (global navigation satellite system) — GNSS is the umbrella term for the satellite constellations that provide positioning, navigation and timing — GPS, Galileo, GLONASS and BeiDou.
- Ground sample distance (GSD) — Ground sample distance (GSD) is the real-world distance on the ground covered by one pixel of a satellite or aerial image — the core measure of spatial resolution.
- TLE (two-line element set) — A TLE (two-line element set) is a compact, standardized text format that encodes a satellite's orbit at a specific moment in two 69-character lines.
- SGP4 — SGP4 is the standard mathematical model that turns a satellite's TLE into a predicted position and velocity at any given time.
- Kessler syndrome — Kessler syndrome is a scenario in which collisions between orbiting objects create debris that triggers more collisions, cascading until parts of low Earth orbit become hazardous to use.
- Conjunction — In satellite tracking, a conjunction is a close approach between two orbiting objects — a predicted near-miss operators watch in case a collision-avoidance manoeuvre is needed.
Space weather
- Kp index — The Kp index is a 0–9 scale of global geomagnetic activity over three-hour periods, and it is the number aurora watchers check to judge tonight's odds.
- Geomagnetic storm — A geomagnetic storm is a temporary disturbance of Earth's magnetic field driven by bursts of solar wind and coronal mass ejections from the Sun.
Sky & observing
- Azimuth — Azimuth is the compass direction to an object in the sky, measured in degrees clockwise from true north — 0° is north, 90° east, 180° south, 270° west.
- Twilight (civil, nautical, astronomical) — Twilight is the period before sunrise and after sunset when the sky is partly lit by the Sun below the horizon, split into civil, nautical and astronomical stages.
- Aphelion (& perihelion) — Aphelion is the point in a body's orbit around the Sun where it is farthest from the Sun; perihelion is the closest point.
Live data, by question
- How many satellites are in orbit?A live count of active satellites and tracked objects, updated from the public catalogue.
- How many Starlink satellites are there?The current number of Starlink satellites in orbit, with launch and deorbit trends.
- How much space debris is there?How many tracked debris objects and estimated fragments orbit Earth right now.
- How much does it cost to launch to space?The falling cost of reaching orbit, per kilogram, across rockets and decades.
- Live satellite statisticsThe full CC-BY dataset: objects by orbit, country and constellation — free to cite and reuse.
Live trackers
- Where is Artemis II right now?Live distance from Earth and the Moon, mission phase and splashdown countdown for the Orion crew.
- Where is the James Webb Space Telescope?JWST's live distance from Earth at Lagrange point L2, and why you can't see it in the sky.
- Where is the Hubble Space Telescope?Track Hubble live in low Earth orbit and see when it passes over your city.
- Track Starlink liveSee every Starlink satellite on a live map, plus the 'Starlink train' after each launch.
- Track the ISS liveThe International Space Station's live position, ground track and next pass over you.
- Live satellite trackerSee thousands of satellites orbiting Earth in real time, computed live in your browser.
Identify & tonight
- What is that light in the sky?Identify a moving light overhead — satellite, ISS, planet, plane or Starlink train.
- Can I see the aurora tonight?Live northern-lights forecast for your city: tonight's Kp versus the Kp you need.
- What is the Moon doing tonight?Tonight's Moon phase, rise and set times, and how bright the sky will be.
- How active is the Sun right now?Live solar-flare, sunspot and solar-wind readings that drive space weather and auroras.
- When is the next meteor shower?Peak dates, hourly rates and the best viewing window for every major meteor shower.
- Where do rockets launch from?A map and directory of the world's active spaceports and their launch pads.
