Frequently Asked Questions

What does "distance to Mars" actually mean on this site?

It's the real, straight-line distance between Earth and Mars right now, worked out from each planet's actual position in its orbit at this moment — not a textbook average and not the record closest approach. Because Earth and Mars orbit the Sun at different speeds and different distances, that live number is constantly changing, sometimes by millions of kilometres in a single week. The calculator shows today's real figure; the Earth–Mars distance article explains why the swing is so large.

How often is the distance updated?

The positions are recalculated continuously from the underlying orbital model, so the number reflects the current moment rather than a value cached once a day. Planetary motion is smooth and gradual, so you won't see it jump — but check back tomorrow and the figure will have shifted, especially for planets whose orbits carry them quickly relative to Earth, like Mars or Venus.

Why does the site show a distance that looks different from what I read elsewhere?

Most published "distance to Mars" figures are the average distance or the closest-approach record — a single fixed number that gets repeated everywhere. This site calculates the current position of each body and reports the real, live distance, which is almost never the same as that average. See also: the difference between average and current distance further down this page.

What is light-time delay, and why does it matter?

Light-time delay is simply how long it takes light — or any radio signal, which travels at the same speed — to cross the distance between two points. It matters enormously for spacecraft, because it sets a hard physical floor on how fast a command can be sent and a response received. There's no way to engineer around it; the only way to reduce the delay is to reduce the distance. The full explainer covers why this forces Mars rovers to make many of their own driving decisions.

How long does a signal take to reach Mars?

Anywhere from about 3 minutes at closest approach to roughly 22 minutes when Mars is on the far side of the Sun. That means a full round-trip — command sent, response received — can take up to 44 minutes, which is why real-time joystick control of a Mars rover simply isn't possible.

Does light-time delay change over the course of a mission?

Yes, continuously. As Earth and Mars move along their orbits at different speeds, the delay grows and shrinks over a period of months, not days. Mission teams plan around this, scheduling more autonomous operation during the months when the delay is longest.

What is the closest Mars has ever been to Earth?

The closest possible approach is around 56 million kilometres. That specific configuration is rare, because it requires Mars to be near the closest point in its elliptical orbit (perihelion) at the exact same time Earth catches up to it — a coincidence of timing that happens only once every fifteen to seventeen years. Most oppositions land somewhere between 75 and 100 million kilometres instead. More detail in the Earth–Mars distance article.

How long would it take to travel to Mars?

Most robotic missions take 6 to 9 months one-way, using a fuel-efficient transfer orbit that follows a wide curved path rather than a straight line. Faster trajectories are possible but burn far more fuel, and slower ones save fuel at the cost of a longer flight. The travel-time article breaks down how the launch date and trajectory choice affect the total.

Why don't we launch to Mars whenever we want?

Launch windows open roughly every 26 months, when Earth and Mars are positioned so that an efficient transfer trajectory actually reaches Mars. Launching outside that window is still technically possible, but it costs dramatically more fuel — often more than any realistic rocket can carry. See how launch windows are chosen for the full reasoning.

Why does the Moon's distance from Earth change?

The Moon's orbit is an ellipse, not a perfect circle, so its distance from Earth swings between roughly 356,500 km at its closest and 406,700 km at its farthest over the course of about a month. The difference is large enough to be visible to the naked eye — a "supermoon" is simply a full moon that happens to coincide with the close end of that cycle. Full details in the Moon distance article.

What's the difference between perigee and apogee?

Perigee is the point in the Moon's monthly orbit where it comes closest to Earth; apogee is the point where it swings farthest away. Each happens roughly once per lunar month, and the two points aren't fixed in space — they slowly rotate over time, which is why "supermoons" don't happen on a perfectly regular schedule.

How far is Jupiter from Earth?

Jupiter's distance from Earth ranges from about 588 million kilometres at its closest to roughly 968 million kilometres at its farthest, since both planets' elliptical orbits add up in different ways depending on where each one currently sits. Even at closest approach, light takes over half an hour to make the trip. See the Jupiter distance article for the full range and how it's calculated.

How far is Voyager 1 from Earth right now, and is it still transmitting?

Voyager 1 is over 24 billion kilometres from Earth and counting — it's the most distant human-made object ever built, and its distance grows by roughly 61,000 km every hour as it continues outward. It is still transmitting data back to Earth, though its radio signal now takes close to a full day to arrive. The Voyager 1 article has the live figure and mission background.

Will Voyager 1 ever leave the solar system?

In one sense it already has: Voyager 1 crossed the heliopause and entered interstellar space in 2012, leaving the bubble of particles the Sun blows around itself. But it's still well within the Sun's gravitational influence, and won't clear the outer Oort Cloud — the true edge of the solar system — for roughly another 30,000 years.

How far away is the International Space Station?

The ISS orbits at roughly 400 to 420 kilometres above Earth's surface — closer than the distance between many major cities — while circling the entire planet about every 93 minutes, or roughly 16 times a day. Its altitude drifts slightly due to atmospheric drag and gets periodically boosted back up by docked spacecraft. Full details in the ISS distance article.

Why does the ISS look so much closer than the Moon?

Because it genuinely is — by a huge margin. The ISS sits about 400 km up, while the Moon orbits around 384,000 km away on average, making the Moon roughly a thousand times farther from Earth than the space station.

What data does this site use to calculate distances?

Positions come from the VSOP87 planetary orbital model, a well-established analytical method for computing where each major planet sits at a given moment in time. It's the same family of model widely used in planetarium software and astronomy education tools.

How accurate are these numbers?

Accurate to within a few percent of the true range — precise enough to understand scale, trends, and how dramatically distances swing over time, but not precise enough for spacecraft navigation or scientific publication. See the terms and conditions for the full accuracy note.

What's the difference between "average distance" and "current distance"?

Average distance is calculated by smoothing out every possible position over a long stretch of time — useful for comparing planets in general, but it tells you nothing about today. Current distance is where the planets actually are right now, which can sit far above or below that average depending on where each one happens to be in its orbit. A quoted "average" of 225 million km for Mars, for instance, is rarely close to the live number on any given day.

Which planet is closest to Earth on average?

Somewhat counterintuitively, it's Mercury — not Venus or Mars. Averaged over long periods and every possible orbital alignment, Mercury spends more time closer to Earth than either neighbour, even though Venus or Mars will each be nearer on any individual day. The closest-planet article walks through the math behind that result.