You can find and follow near-Earth asteroids online without owning a telescope. Use NASA/JPL’s CNEOS tools according to the task: NEO Lookup for a known designation, NEO DB Query to filter the catalog, What’s Observable to plan objects from a location and date, Sky Search to identify known bodies in a sky field, Small-Body Database (SBDB) for orbit and physical data, and Horizons for time-specific predicted positions. Use Scout for unconfirmed, short-arc candidates and Sentry for confirmed near-Earth objects with possible impacts over roughly the next century.
Online tracking means reading an orbit and generating ephemerides. Physically observing an asteroid, or submitting your own astrometric measurements, is a separate activity with stricter equipment and reporting requirements.
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What counts as a near-Earth object?
NASA/JPL defines a near-Earth object (NEO) as an asteroid or comet whose orbit brings it within 120 million miles (195 million kilometers) of the Sun. That orbital definition includes many bodies that never come particularly close to Earth.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallA potentially hazardous asteroid (PHA) is a narrower category. NASA/JPL describes a PHA as an asteroid larger than about 460 feet (140 meters) whose orbit can come within 4.6 million miles (7.5 million kilometers) of Earth’s orbit. The designation describes size and orbital geometry, not a prediction that an impact will occur.
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Size estimates are not equally available for every object. A catalog may contain a diameter or albedo value for one asteroid and leave that field blank for another. An absent value means the property has not been measured or constrained sufficiently; it does not establish that the asteroid is small. Likewise, being a NEO or PHA does not by itself say whether the object is above your horizon tonight.
Choose the NASA tool that matches your question
| What you want to do | Tool | What you get | Key limitation |
|---|---|---|---|
| Look up an asteroid you already know | CNEOS NEO Lookup or SBDB Lookup | Orbital elements, physical parameters and related object information | The result is the best available solution from current observations, not perfect certainty about every future position. |
| Filter the known population | NEO DB Query or SBDB Query | Objects matching selected orbital or physical criteria | Results depend on the constraints you select and on what has been cataloged. |
| Find known objects in a particular patch of sky | Sky Search or Small-Body Identification | Known bodies expected in a specified field, time and location | This identifies cataloged objects; it is not a discovery survey. |
| Plan an observing night | What’s Observable or Small-Body Observability | Objects meeting the service’s observability criteria for a site and date | “Observable” does not guarantee an easy visual detection with consumer equipment. |
| Calculate a position for an exact time | Horizons | An ephemeris: predicted coordinates, distance and other quantities over chosen times | Predictions inherit the orbit solution and its uncertainty. |
| Inspect possible long-term impacts | Sentry | Potential future impact solutions for confirmed NEOs | A listing represents conditional possibilities allowed by current uncertainty, not an expected collision. |
| Check a newly reported candidate | Scout | Preliminary short-term assessment of unconfirmed candidates | Candidate designations are provisional, detections can be artifacts, and ratings are not rigorous probabilities. |
The most useful comparison is not which tool is “best,” but which question it answers. Lookup and database queries concern identity and population. What’s Observable and Sky Search concern the sky from a particular site and time. Horizons propagates an orbit into a time series. Scout and Sentry address different stages of uncertainty and risk.
How to find a known asteroid by designation
Use CNEOS NEO Lookup
- Open the CNEOS NEO Lookup page.
- Enter the asteroid’s designation or name exactly as published. A provisional designation, such as a year-letter-number format, is often more reliable than an informal nickname.
- Review the returned orbit, close-approach information and physical data. Note the observation arc and uncertainty indicators when shown.
- For a position at a particular time, continue to Horizons rather than treating the lookup page’s orbital elements as a sky chart.
If the lookup returns no match, check punctuation, spacing and whether the object is a comet or another small-body type. A newly reported candidate may not yet have a permanent or officially confirmed designation. Names can also change as an object receives a permanent number, so retain the identifier shown by the service when moving between tools.
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Use SBDB when you need the underlying orbit record
The Small-Body Database stores orbital and physical parameters for cataloged small bodies. It is useful when you need elements, solution dates, observational history or a machine-readable record rather than a simple summary. Treat the listed orbit as a fitted solution based on available observations; future positions become less certain as you project farther from the observation span.
SBDB is also a useful checkpoint when two pages appear to disagree. Confirm that both pages refer to the same designation, solution epoch and object type. An orbit is a model fitted to measurements, not a permanent track painted onto the sky. New observations can change the fitted parameters and therefore alter later ephemerides.
Search the catalog instead of starting with a name
Filter with NEO DB Query
NEO DB Query is appropriate when your question sounds like “Which known near-Earth asteroids are larger than a given size?” or “Which objects have a particular orbital inclination or eccentricity?” Select the available orbital and physical constraints, run the query and inspect the matching records. Tightening several filters can produce an empty result even when each individual condition is common.
Use broad criteria first, then narrow the list. For example, begin with the NEO population and one orbital condition, review the count, and add a physical constraint only after confirming that the desired field is populated. Save the exact constraints with the result so another person can reproduce the search.
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Understand what a catalog filter does not tell you
- A database result is limited to known and cataloged objects that satisfy the selected fields.
- Missing diameter, albedo or other physical values do not prove the object is small; the parameter may simply be unmeasured.
- Population searches do not replace an ephemeris calculation when you need a position for a particular night.
- A filter hit does not establish that an asteroid is currently close to Earth, bright enough to image or visible from your site.
Find asteroids in a specific part of the sky
Use Sky Search or Small-Body Identification
- Enter the observing date and time, your geographic location or observing site, and the sky region or field of view.
- Run the search to obtain known objects expected in that region at that time.
- Compare the returned positions with your image or planned pointing. Use Horizons if you need a denser time series or additional coordinate systems.
Record whether the input coordinates describe the center and size of your field or the corners, and keep the time standard with the result. A few minutes can matter for a close, fast-moving object. If you are matching an image, use the image midpoint and an accurate field of view rather than an approximate pointing.
The result is a cross-match against known bodies. A faint moving point absent from the list may be an uncataloged object, an image artifact or a known object whose input time, coordinates or field size were entered incorrectly. The service is not a replacement for a wide-field discovery survey. Identification tools answer “which known objects should be here?” They do not certify that every moving point in an image is an asteroid.
Plan an observing night with What’s Observable
- Choose the observing location or site.
- Set the date and the night interval you intend to use.
- Run What’s Observable (also called Small-Body Observability in related interfaces).
- Sort or inspect the returned objects using the available altitude, brightness, elongation and timing fields.
- For a selected target, generate a Horizons ephemeris at intervals short enough to account for its apparent motion.
Use the list as a planning screen, not a promise. “Observable” is a software criterion, and practical detection depends on apparent brightness, Moon and twilight, transparency, light pollution, tracking accuracy, exposure strategy, detector sensitivity and the object’s rate of motion. NASA’s public pages do not guarantee that a consumer telescope can show a particular target.
An object can satisfy the service’s criteria yet be a poor first target because it is low in the sky, moving quickly, near the Moon or fainter than your camera’s useful limit. Conversely, a target that is technically listed may become easier after twilight ends or when it reaches a higher altitude. Check the full night rather than assuming the object is equally favorable at every listed time.
Generate a trackable path with Horizons
Horizons turns an orbit solution into an ephemeris: a table of predicted positions and related quantities for selected times and an observing site. It is the appropriate tool when “track” means knowing where the asteroid should be at 21:00, 21:05 and 21:10 UTC.
- Choose the target by its official designation or database identifier.
- Select an observer location. A geocentric result and a specific observatory can differ, especially for a close approach.
- Set the date and time span, time step and output format.
- Select coordinates appropriate to your use, such as right ascension and declination for a telescope mount or altitude and azimuth for a local sky view.
- Include range, rate of motion, magnitude estimates and uncertainty-related fields when available.
- Generate the ephemeris and save the output with its time scale and coordinate settings.
Use the same time standard, epoch and location when transferring coordinates to planetarium or mount software. For a fast-moving close approach, a coarse one-hour table can miss useful detail; request shorter intervals and regenerate the table if the observing site or time changes.
Right ascension and declination are convenient for equatorial mounts, while altitude and azimuth are intuitive for a local horizon view. Neither coordinate choice improves the underlying orbit. The range and rate fields help explain why a target may move noticeably between exposures, and an estimated magnitude remains an estimate rather than a guarantee of camera or visual detectability.
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How NASA turns observations into an orbit
Wide-field survey telescopes image large areas and report measured positions of moving objects. The Minor Planet Center (MPC) is the public archive for small-body astrometric observations. Follow-up observers add positions on later nights, extending the observation arc.
CNEOS uses MPC observations to calculate orbit solutions. Its process includes complete astrometric data sets, data weighting and debiasing, perturbation models and numerical methods. The resulting orbit and uncertainty information is archived through SBDB. As more high-quality positions arrive, the range of allowed orbits normally narrows, although unusual observations or systematic errors can require a revised solution.
The observation arc matters. A few positions collected over a short interval can fit multiple plausible trajectories, while measurements separated across nights or apparitions usually constrain the orbit better. That is why a new candidate can have a broad range of predicted positions and why an older object’s ephemeris can still be revised after additional astrometry.
In everyday use, “tracking” usually means following this published orbit and requesting updated ephemerides. In the professional and amateur-observer system, tracking can also mean collecting repeated astrometric measurements. A casual visual sighting is not automatically a usable measurement; observers who want to contribute should follow MPC observing, calibration and reporting standards. The public tools let you investigate an object without making any observation yourself.
Scout and Sentry answer different risk questions
Scout: unconfirmed candidates
Scout monitors objects listed on the MPC NEO Confirmation Page before they are confirmed. Their provisional designations are unofficial, and some detections may be artifacts. Scout provides a short-term assessment intended to help observers decide which candidates deserve follow-up.
Scout’s indicators are especially sensitive to a short observation arc. They are screening signals, not rigorous probability assessments. A high-interest indicator means that follow-up may be valuable, not that an impact is predicted. Once a candidate is confirmed and receives a reliable orbit, it leaves the confirmation page and long-term monitoring shifts to Sentry.
Sentry: confirmed objects and long horizons
Sentry continuously searches the current catalog of confirmed NEOs for possible future Earth impacts over approximately the next 100 years. A risk-page entry can occur because the available observations still allow several orbital solutions, with some mathematically intersecting Earth.
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That entry is conditional. Additional observations can eliminate the impact-compatible solutions and remove the object from the list. Therefore, a Sentry listing means “this possibility remains in the current uncertainty range,” not “an impact is expected.” Treat the page as a live monitoring result whose contents can change when the orbit is improved.
NASA/JPL’s Asteroid Watch page currently states that there is no known significant impact threat for the next hundred years or more. Because that status can change as observations improve, consult the live page for the current statement rather than treating it as permanent.
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The JPL SSD/CNEOS API exposes machine-readable services for Horizons, close approaches, object identification, observability, SBDB, Scout and Sentry. An API workflow is useful for scripts, dashboards or repeated date scans:
- Query an object or catalog endpoint and store the identifier returned by the service.
- Request an ephemeris for explicit start time, stop time, step size and observer location.
- Record the query date and returned uncertainty or solution metadata with your results.
- Handle empty results, rate limits and changed designations instead of assuming every request succeeds.
- Validate units, time scales and coordinate conventions before plotting or sending positions to another program.
If you are not comfortable with JSON and parameterized requests, the human-facing CNEOS pages are the simpler route and expose the same conceptual workflow. An API response is not automatically more accurate than the web page; it is simply easier to process repeatedly and consistently.
Troubleshoot common problems
“The asteroid is not visible where the chart says”
- Verify the date, time scale and geographic coordinates.
- Check whether the target is below the horizon, in twilight or too close to the Moon.
- Compare the predicted magnitude with your camera or telescope’s practical limit.
- For a rapidly moving object, regenerate Horizons output with shorter time steps.
- Confirm that the mount or planetarium program is using the same coordinate frame and epoch as the ephemeris.
“The tool shows no objects”
- Widen the field of view or date range.
- Relax one filter at a time in NEO DB Query.
- Confirm that the object is a known, confirmed body rather than a Scout candidate.
- Check that the selected observatory site is in the intended hemisphere and longitude.
- Make sure the requested altitude, brightness or elongation limits are not excluding every result.
“A risk score looks alarming”
Read the object’s observation arc, uncertainty and possible-impact dates, then check whether the entry changes after new observations. Do not interpret a conditional Sentry solution or a preliminary Scout rating as a forecast of a collision. Look for the distinction between a possible orbit and the most likely orbit; the existence of the former is why monitoring pages can list an object at all.
What you need—and what you do not
Searching catalogs, reading orbit solutions, generating Horizons ephemerides and viewing Sentry or Scout pages require only an internet connection. A telescope is optional. Actual observation requires a suitable site, equipment matched to the target’s brightness and motion, accurate timing and careful image reduction. Submitting measurements requires compliance with MPC standards; an uncalibrated snapshot is not enough to refine an official orbit.
The Tool Desk
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For most readers, the reliable sequence is: identify or filter an object, check its observability, generate a site-specific ephemeris, and then interpret any Scout or Sentry result in the context of uncertainty. You can complete that entire sequence online before deciding whether an observing attempt is worthwhile.
Frequently Asked Questions
How do I find an asteroid using NASA’s website?
Start with CNEOS NEO Lookup if you know the designation. Use NEO DB Query to search by orbital or physical properties, Sky Search to identify known objects in a specified field, and What’s Observable to find candidates for a location and date.
How can I track a near-Earth asteroid’s path?
Look up the object in SBDB, then use Horizons to generate an ephemeris for your observing site, date, time step and preferred coordinates. Save the time scale, location and settings with the output.
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What’s Observable, also presented as Small-Body Observability in related interfaces, lists objects meeting its criteria for a selected site and night. Check altitude, brightness, twilight, Moon position and equipment limits before attempting an observation.
What is the difference between Scout and Sentry?
Scout evaluates unconfirmed candidates on the MPC NEO Confirmation Page over a short horizon. Sentry monitors confirmed NEOs for possible impacts over approximately the next 100 years. Scout ratings are preliminary; Sentry entries are conditional on orbital uncertainty.
Does a Sentry risk listing mean an asteroid will hit Earth?
No. It means that some orbits still allowed by current observations intersect Earth. Further observations can narrow the uncertainty and remove the object from the list; a listing is not a prediction that impact is expected.
Can I use these tools without a telescope?
Yes. Catalog searches, orbit inspection, ephemeris generation and risk-page checks require only internet access. A telescope is optional and does not guarantee that a particular asteroid will be detectable.
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Can a faint moving point missing from Sky Search be a new asteroid?
Possibly, but it could also be an image artifact, an input error or a known object outside the requested field or time. Sky Search cross-matches known bodies; it is not a discovery survey. Formal reporting requires calibrated astrometry and MPC procedures.
The Bottom Line
Use CNEOS NEO Lookup or SBDB to identify an object, NEO DB Query to filter the catalog, What’s Observable to plan a site and night, Sky Search to match known bodies to a field, and Horizons to calculate positions at exact times. Use Scout only for preliminary unconfirmed candidates and Sentry for conditional long-term impact monitoring. The tools are free to use online; observing and submitting measurements are optional activities with additional practical and reporting requirements.
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