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 real Keplerian orbit from NASA/JPL elements, and animates the flybys so you can watch them sweep past Earth. 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 jumps the clock to that flyby and animates it past Earth.
• 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.

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).
• 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.

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 jumps to it and animates). 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. Dismiss it with × — it 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, /?object=99942 opens straight on Apophis. Browser back/forward moves through your selections.

14How 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.
• The orbits drawn on the map are a simplified two-body Keplerian propagation from a single set of osculating elements. They're accurate to the eye for a top-down inner-solar-system view, but they do not model the orbit-bending a close Earth pass imparts, nor longer-term planetary perturbations. So a rendered path — especially after a deep encounter like Apophis 2029 — is indicative, not predictive.
• Sizes are exact when measured, otherwise estimated from absolute magnitude and an assumed albedo — a several-fold range for dark vs. bright surfaces.

15Controls 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.

16Glossary

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 — what the map propagates.

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.

17Frequently 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.

18Data 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.
• Coastlines: Natural Earth via world-atlas.

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19Feedback

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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