ASTEROID TRACKER · HELP

1What this is

Asteroid Tracker is a live, interactive view of the near-Earth asteroids passing by our planet — it shows where they are, the orbits they ride, and how close they come.

A near-Earth object (NEO) is an asteroid whose orbit brings it close to Earth's. This tool plots every catalogued close approach over a ±70-day window, places each object on its orbit from NASA/JPL, and animates the flybys on real JPL Horizons ephemerides so the passes sweep past Earth at their true miss distances. Alongside the heliocentric map you get a top-down close-approach geometry, estimated sizes and impact energies, JPL Sentry impact-risk flags, and recent atmospheric fireball detections.

2Quick start

• Look at the center map. The Sun is in the middle, Earth is the blue dot on its orbit, and each colored dot is an asteroid riding its real ellipse. Color = how close it passes.
• Pick an asteroid. Click a dot, or a row in the close-approach catalog on the left. The app snaps the clock to that object's closest approach, framing where it really passes Earth — press space to animate the flyby from there.
• Watch the dashboards on the right — the Earth-proximity inset shows the miss distance against the Moon's orbit; the detail card breaks down size, speed, orbit, and energy.
• Press space to play time forward, or drag the timeline at the bottom. Press N (or NOW) to snap back to real time.

3The heliocentric orbit map

The central canvas is a top-down view of the inner solar system, looking down on Earth's orbital plane.

• The Sun sits at the center. Earth is the blue dot, moving along its orbit (the ring). Earth's position is computed for whatever moment the clock shows.
• Each asteroid rides its real elliptical orbit, drawn from JPL's osculating elements. The dot marks where it is at the current moment; the faint ellipse is its full path.
• Dot color encodes the miss distance of its closest pass — red inside the Moon's orbit, cooling to teal far out:

• Dot size scales with the asteroid's estimated diameter, and PHAs get a pulsing red ring.
• The selected object is highlighted with a white ring and a brighter orbit.

Navigating

• Scroll / pinch to zoom, drag to pan. The ⤾ view button resets the framing.
• Hover a dot for a quick tooltip (size, speed, miss distance, date). Click it to select.
• ◯ orbits toggles the orbit paths, labels toggles on-map text, and ⊕ Earth-lock pins Earth to the center so you can scrub the timeline and watch asteroids sweep past a fixed Earth.
• ⧉ Isolate (in the transport bar) hides every asteroid except the selected one, so you can study a single orbit and its flyby without the rest of the field. Select a different object and the isolation follows it; toggle it off to bring everyone back.

4Time & playback

The tracker is a time machine: it can sit at the live moment, run forward to upcoming passes, or rewind to recent ones.

• The clock (top-left of the map) shows the displayed moment with a tag: LIVE (real time now), … AGO (the past), or +… FORECAST (the future).
• ▶ Play/pause animates time forward at the selected speed (also space).
• NOW snaps back to live real time (also N).
• ⏭ next skips to the next close approach after the displayed moment and plays through it (also ]). While playing, a colored ring shrinks onto Earth as the pass approaches, and a flash marks the instant of closest approach.
• Speed buttons set how fast time runs (simulated minutes-to-days per real second).
• The timeline at the bottom is a scrubber; dots mark each close approach. Selecting a far-future pass (e.g. Apophis in 2029) automatically reframes the timeline around it so the playhead stays on the bar.

5Close-approach catalog (left panel)

Every catalogued close approach in the window, from NASA/JPL CNEOS. The count next to the title shows how many are visible vs. total. The list is sorted by closest miss first — the asteroid that passes nearest Earth sits at the top.

Search

The search box filters the list by name or designation — type apophis to jump straight to 99942 Apophis 2004 MN4, or a number like 2024 to list that year's objects. Search looks across the whole catalog and ignores the distance filter, so you'll always find what you type; the count shows how many matched. Press Esc to clear.

Reading a row

Each row shows the object's name and its miss distance, the estimated diameter, the relative speed, and its orbit class code. The arrow tag shows the approach time (→ upcoming, grey for past). Badges flag special status:

Click a row to select it — the map snaps to its closest approach, framing the real geometry of the pass (press space to animate it). Use ↑/↓ to move through the list.

6Distance-class filters

The chips above the list filter both the catalog and the map by miss distance in lunar distances. Each class is color-matched to the map, and the chip shows how many objects fall in it. Click a chip to show or hide that class.

7Selected asteroid card (right panel)

When you select an asteroid, this card breaks it down:

• Verdict — how close the pass is, in lunar distances, color-coded by closeness.
• Diameter & comparison — measured or estimated size, with a familiar real-world reference.
• Absolute magnitude (H) and orbit class (Aten, Apollo, Amor…).
• Earth MOID and the orbital elements (semi-major axis, eccentricity, period).
• Close approach — the date, miss distance, relative speed, and a hypothetical impact energy (these objects miss).
• Sentry box — if the object is on the impact-risk list: the odds, time window, and Palermo scale.
• A link to the object's JPL Small-Body Database entry.

8Inbound close-pass warning

When an asteroid is genuinely en route to a close pass, a pulsing banner appears over the map. It fires only for meaningful passes — within 5 lunar distances and within the next ~400 days — and shows the strongest (closest, largest), then soonest.

The banner carries a severity chip, the object's name, the miss distance in LD, and a countdown. Its color and pulse rate scale with severity. Click the banner to load that asteroid (it selects and frames the pass, like a list click) — clicking does not dismiss it. To dismiss, use the ×; it then stays hidden until a different object becomes the top threat.

9Earth-proximity inset (right panel)

A top-down map of Earth's immediate neighborhood that answers "how close, and inside or outside the Moon?" at a glance.

• Earth sits at the center; the solid ring is the Moon's orbit (1 lunar distance), with dashed reference rings at larger distances that scale to fit the selected pass.
• The Moon is marked on its ring at the displayed moment.
• The selected asteroid sweeps past on a straight flyby track, with the closest-approach point marked at its real miss distance. Passes inside the Moon's ring are flagged in red.

10Recent fireballs (left panel)

Atmospheric impact (bolide) detections from CNEOS over recent months, newest first. These are small objects that did enter the atmosphere and burn up — a real-world counterpart to the flybys above.

• Each row shows the date, the location (if reported), and the impact energy in kilotons of TNT.
• Energy is color-graded: C small, M moderate, X large.

11Approach charts

• Close-approach scatter — each catalogued pass plotted by time (x) against miss distance in LD (y, log scale), dot size by diameter and color by closeness. A dashed line marks the Moon at 1 LD; a vertical line marks now.
• Miss-distance histogram — how the visible objects distribute across the distance classes (<1, 1–5, 5–20, 20–50, 50+ LD).

Both charts respect the distance filters, so hiding a class updates them too.

12Sub-lunar watchlist

The live feed only covers a ±70-day window, so a famous pass years away — like Apophis on 13 April 2029 — wouldn't otherwise appear. To fix that, the tracker also loads every known sub-lunar (< 1 LD) approach out to 2100, regardless of date, and merges them in.

• These objects carry a TRACKED badge and headline their closest pass (the reason they're worth watching).
• Because they're < 1 LD, they sort to the very top of the catalog and appear in the <1 distance filter.
• Selecting one reframes the timeline to its pass and animates the real flyby — for Apophis, the 0.1 LD encounter in 2029, inside the geostationary ring.

13Sharing & deep links

The URL always reflects the selected object. Selecting an asteroid adds ?object=<designation> to the address bar, and opening that link selects the object directly — exactly like clicking it in the list, including the jump to its flyby. For example, /live?object=99942 opens straight on Apophis. Browser back/forward moves through your selections. Add &view=flyby to also isolate the object and zoom into the lunar-distance framing of its pass — /live?object=99942&view=flyby is the full cinematic view.

14Will I see it? — the sky view

Every asteroid profile page (/asteroid/<designation>, or the ☀ Will I see it? button on the selected-asteroid card) turns the flyby into your sky. Type a city or lat, lon, or press ◎ my location, and the page asks JPL Horizons for the object's position and brightness from that spot every 20 minutes across the pass ±2 days, plus the Moon.

• The dome is an all-sky chart: zenith at the centre, horizon at the rim, north up and east on the left (the way a star map reads when held overhead). The bright arc is the object's path during the best dark session, ticked in local hours; fainter arcs are other nights and the daytime portions. The white marker is the best moment; the grey disc is the Moon.
• The verdict is one of Naked eye (≤ mag 6 from a dark site), Binoculars (≤ 9.5), Small telescope (≤ 13), Large amateur telescope (≤ 16.5), Professional telescopes only, or Not observable from here — with when, where to look (compass direction and altitude), the observing window, the Moon's phase, and other nights that also work.
• The strip below shows altitude (blue area) and brightness (amber line) across the whole window, with daylight and twilight shaded, so you can see at a glance which nights it is up after dark.

Brightness is Horizons' predicted apparent magnitude for your site, with a rough allowance for atmospheric dimming near the horizon. City skies cut the naked-eye limit to roughly mag 4; haze, twilight and moonlight all make targets harder. "Dark" means the Sun more than 12° below the horizon; the object must be at least 10° up. Nothing here is a guarantee — it is where and when to try.

15Uncertainty & the blind spot

Most orbit visualisers draw a crisp line. The honest picture is a corridor, so the tracker shows how sure the numbers are — and where surveys cannot look.

• 3σ corridor. JPL publishes a minimum and maximum distance for every close approach. The Earth-view inset draws that band around the pass (and captions it when it is too narrow to draw); the selected-asteroid card lists it as Miss corridor, with the timing uncertainty; the profile page plots it on a log scale from Earth's surface to 100 LD, and shows it under every row of the encounter table.
• Orbit quality. The condition code (0 = tightly pinned … 9 = barely constrained), the observation arc and the number of measurements in the fit. A short arc means the corridor will move as observations accumulate.
• First seen. The date of the first observation, compared with the pass. FOUND AFTER PASS marks an object whose first observation came after closest approach — nobody saw it coming. NEW marks objects first observed within the last two weeks.
• The daylight blind spot (☼ glare, key G). Ground-based surveys can only search the night sky, so anything within about 60° of the Sun as seen from Earth is invisible to them. The map draws that wedge from Earth toward the Sun; markers inside it go hollow, and the hover tooltip says so. FROM THE SUN flags objects that arrive out of that wedge (elongation under 60° five days before the pass) — the Chelyabinsk geometry.
• Sentry virtual impactors. For objects on JPL's risk list, the profile page draws every virtual impactor on a timeline — each is an orbit still consistent with all observations that would hit on that date. They vanish as measurements rule them out, which is how objects leave the list.

16Discovery feed (right panel)

The Discovery feed card streams the Minor Planet Center's NEO Confirmation Page — objects spotted in the last hours or days that no one has confirmed yet. Each has only a temporary designation, a sky position, a brightness and a handful of observations. The all-sky chart plots them against the ecliptic, the Sun and its glare zone, and the opposition point where surveys look hardest; dots found today pulse green. The list shows the newest, with a rough size from brightness and the MPC's NEO score. Below it, Confirmed & catalogued this week closes the loop: objects first observed within the last ten days that already have a catalogued close approach — click one to select it on the map. The feed refreshes every ten minutes.

17Flyby calendar & sharing

Subscribe to webcal://www.asteroidtracker.ai/api/calendar?ld=5 (link in the About card) and every pass within 5 lunar distances over the next year — plus every sub-lunar pass to 2100 — lands on your calendar with an alarm an hour before. Change ld for a tighter or looser list (?ld=1 for sub-lunar only), add &days=730 for a two-year horizon, or ?des=99942 for one object's passes. 📅 Calendar on the selected-asteroid card downloads that object's flybys as an .ics file.

↗ Share hands the asteroid's profile link to your device's share sheet (or copies it). Profile links carry their own preview image — the actual encounter geometry, miss distance and date — so a shared link shows the pass, not a generic banner.

18How accurate is it?

Two things are worth separating: the numbers and the drawn orbits.

• Miss distances, dates, and speeds come straight from JPL's CNEOS close-approach catalog, which uses full numerical integration with planetary perturbations. Those figures are authoritative.
• Positions near close approaches are JPL's own ephemeris. The server samples JPL Horizons state vectors (full N-body integration) for ±3 days around every approach within 20 LD — plus Earth and Moon — and the map interpolates those samples for the asteroid markers, flyby tracks, and the Earth-view inset. There, the drawn geometry matches the catalog by construction: Apophis really does thread the geostationary ring at 0.10 LD.
• Away from the passes, the faint orbit ellipses are a simplified two-body Keplerian propagation from osculating elements — a good orbit shape for context, but not a precise clock, so markers far outside their Horizons window can drift from their true position (Earth itself rides a real elliptical orbit).
• Sizes are exact when measured, otherwise estimated from absolute magnitude and an assumed albedo — a several-fold range for dark vs. bright surfaces.

19Controls reference

Keyboard

Mouse

Map tools

• ◯ orbits — show/hide the orbit paths.
• ⊕ Earth-lock — pin Earth to the center to watch flybys past a fixed Earth.
• labels — toggle on-map text.
• ⤾ view — reset zoom and pan.
• ⧉ Isolate — show only the selected asteroid on the map, hiding all others (in the transport bar).

20Glossary

NEO

Near-Earth object — an asteroid or comet whose orbit comes within 1.3 AU of the Sun.

PHA

Potentially Hazardous Asteroid — a NEO larger than ~140 m whose orbit passes within 0.05 AU (~19.5 LD) of Earth's orbit. About size and proximity, not an expected impact.

Lunar distance (LD)

The average Earth–Moon distance, ~384,400 km (0.00257 AU). Every miss distance here is quoted in LD.

Astronomical unit (AU)

The Sun–Earth distance, ~149.6 million km (~389 LD).

Close approach

The moment an object passes nearest Earth, with a catalogued miss distance and relative speed.

Absolute magnitude (H)

An asteroid's intrinsic brightness — a proxy for size once an albedo is assumed. Lower H = brighter/bigger.

Albedo

Surface reflectivity. A dark (low-albedo) rock must be larger than a bright one to shine equally, which is why sizes from H are a range.

Earth MOID

Minimum Orbit Intersection Distance — the closest the two orbits ever come, independent of where the bodies are. Small MOID is the PHA criterion.

Orbit class

Aten and Apollo asteroids cross Earth's orbit (Atens stay mostly inside it, Apollos mostly outside); Amors approach but stay outside; Atiras stay entirely inside.

Keplerian elements

The six numbers (a, e, i, Ω, ω, M) that define an elliptical orbit and the body's position on it — used for the faint backdrop orbits; positions near close approaches come from JPL Horizons ephemerides.

Sentry

JPL's automated system that continuously scans for any object with a non-zero impact probability over the next ~100 years.

Palermo scale

A measure of an impact risk's significance relative to the random background hazard. Negative values are below background; ≥ 0 merits attention.

Bolide / fireball

A very bright meteor — a small object burning up in the atmosphere, logged by CNEOS with its energy.

21Frequently asked questions

What is a near-Earth object (NEO)?

A near-Earth object is an asteroid or comet whose orbit brings it close to Earth's — within 1.3 astronomical units of the Sun. Most are small and harmless, but a fraction pass closer to Earth than the Moon. Asteroid Tracker plots every catalogued close approach and animates the flyby on each object's real orbit.

How close is one lunar distance (LD)?

One lunar distance is the average Earth–Moon distance, about 384,400 km (0.00257 AU). The tracker measures every miss distance in LD: a pass inside 1 LD is closer than the Moon. For scale, geostationary satellites orbit at about 0.1 LD — which is roughly how close Apophis comes in 2029.

Will an asteroid hit Earth?

None of the objects shown is on an impact course — they are catalogued close approaches that miss. JPL's Sentry system continuously monitors for any object with a non-zero impact probability over the next century; when an object is on that list the tracker flags it and shows the odds, time window, and Palermo scale. Treat everything as indicative, not operational guidance.

What is a Potentially Hazardous Asteroid (PHA)?

A PHA is a near-Earth asteroid larger than about 140 m whose orbit passes within 0.05 AU (about 19.5 lunar distances) of Earth's orbit. The "potentially hazardous" label is about size and orbital proximity over the long term — it does not mean an impact is expected.

How are asteroid sizes estimated?

When a measured diameter exists (from radar or thermal observations) the tracker uses it. Otherwise it estimates size from the asteroid's absolute magnitude H and an assumed reflectivity (albedo). Because dark and bright rocks of the same brightness differ several-fold in size, these estimates are shown as a range, not a precise figure.

What is asteroid 99942 Apophis?

Apophis is a ~340 m asteroid that will pass about 0.1 lunar distance from Earth — inside the geostationary satellite ring — on 13 April 2029, the closest predicted approach of an object its size in modern times. It poses no impact threat: the 2029, 2036, and 2068 risks were ruled out and it was removed from Sentry in 2021. Open it directly at /?object=99942.

Is Asteroid Tracker real-time, and where does the data come from?

Yes. Close approaches come from NASA/JPL's CNEOS Close-Approach Data API, orbital elements and sizes from the Small-Body Database, impact-risk flags from Sentry, and bolide detections from the Fireballs API. It is free to use, with no account required.

For authoritative data, see NASA/JPL CNEOS.

22Data sources & credits

• Close approaches: NASA/JPL CNEOS Close-Approach Data (CAD).
• Orbits & physical parameters: JPL Small-Body Database (SBDB).
• Impact-risk flags: JPL Sentry.
• Fireballs: CNEOS Fireball detections.
• Ephemerides & sky positions: JPL Horizons (heliocentric tracks near every pass; observer tables for the sky view).
• Unconfirmed discoveries: the Minor Planet Center's NEO Confirmation Page.
• Coastlines: Natural Earth via world-atlas.

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23Feedback

This is a one-person project and I'd genuinely like to hear from you — what's useful, what's confusing, a bug, or a feature you'd want. If you teach with it, please say so — I want to make it work better in the classroom.

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