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Asteroid Near-Earth

2004 ER21

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(2004 ER21)

Where is it now

Distance from Sun
0.751 AU
True anomaly
18.25°
Distance from Earth
0.489 AU
As of
20 October 2026

Two-body Kepler propagation — accurate to ~0.1% for major planets over decades, less so for highly-perturbed bodies. Use JPL Horizons for high precision.

Sun Earth — 0.996 AU from the Sun Earth 2004 ER21 — 0.751 AU from the Sun 2004 ER21
Seen from above the ecliptic, north up, to scale. Grid: Earth's orbit in blue. 2004 ER21 is 0.489 AU from Earth today (4.1 light-minutes).

In the sky

Right ascension
16h 54m 31s
Declination
-21° 55′ 13″
Constellation
Ophiuchus
Distance from Earth
0.48 AU
Elongation from the Sun
46.71° — near the Sun — look low at dusk or dawn

Favours the southern hemisphere; low or below the horizon from far north.

From your location

See how high it is right now, whether it is up after civil twilight, and when it rises and sets where you are.

How do I find my coordinates?

Google Maps on a computer

  1. Right-click the spot where you'll be observing.
  2. The first line of the menu is the coordinates, e.g. 51.50722, -0.12758 — click it and they're copied.
  3. Paste them above.

Google Maps on a phone

  1. Press and hold the spot to drop a pin.
  2. The coordinates appear in the search bar (or on the pin's card) — tap to copy, then paste above.

A full Google Maps link works too, but the short maps.app.goo.gl share links don't carry coordinates — copy the numbers instead. We round to about a kilometre; that's all the sky calculation needs.

Know your what3words address? Paste it, e.g. ///filled.count.soap. This is optional — the three words are sent to what3words to convert them, and we don't store the address or the result.

Your location stays in your browser and is sent only for this calculation. Using a what3words address is optional; if you do, the three words go to what3words to be converted and we don't record them. Set a location first, then you can save an email alert for this object. See our privacy policy.

Two-body approximation, good to about a degree for the planets — enough to find the constellation and know whether it is up.

Orbital elements

Semi-major axis
0.899 AU
Eccentricity
0.171
Inclination
7.95°
Orbital period
311.4 days
Perihelion
0.745 AU
Aphelion
1.053 AU
Longitude of ascending node
357.25°
Argument of periapsis
343.53°
Epoch · J2000
2461200.5
Orbit class · ATE
Aten
Earth MOID · 15.9 LD
0.0408 AU
Tisserand (Jupiter)
6.599

Orbit quality

Orbit poorly determined (uncertainty code 7).

Observations used
70
Data arc
10 days
First observed
15 March 2004
Last observed
25 March 2004
Residual RMS
0.51 ″
Solution · Otto Matic
14 April 2021

Visual & observation

Absolute magnitude (H)
24.4

Discovery & classification

Aten Near-Earth Object

Close approaches 30 on record

Flyby geometry
Ecliptic flyby of 2004 ER21 at 2027-01-20 05:26 UTC Top-down view of the ecliptic, Earth at the centre, for the 2027-01-20 05:26 UTC close approach of 2004 ER21. Catalogue miss distance 53.7 LD · 2.06 × 10⁷ km. The curve is the geocentric path from 2027-01-17 to 2027-01-23, with a mark at UTC midnights and an arrow for the direction of motion. The circle is the Moon’s mean orbit; the Moon is plotted at closest approach. A ray shows the Sun’s direction. The labelled distance is the full separation. The drawn radius is the part that lies in the ecliptic plane. At closest approach the object is north of the ecliptic. The path is a geocentric ecliptic ephemeris from JPL Horizons. The inset is a heliocentric view and is approximate. Sun 53.7 LD · 2.06 × 10⁷ km 2027-01-20 05:26 UTC Earth Moon Heliocentric, approximate

Top-down view of the ecliptic, Earth at the centre, for the 2027-01-20 05:26 UTC close approach of 2004 ER21. Catalogue miss distance 53.7 LD · 2.06 × 10⁷ km. The curve is the geocentric path from 2027-01-17 to 2027-01-23, with a mark at UTC midnights and an arrow for the direction of motion. The circle is the Moon’s mean orbit; the Moon is plotted at closest approach. A ray shows the Sun’s direction. The labelled distance is the full separation. The drawn radius is the part that lies in the ecliptic plane. At closest approach the object is north of the ecliptic. The path is a geocentric ecliptic ephemeris from JPL Horizons. The inset is a heliocentric view and is approximate.

JPL Horizons

When (UTC) Body Distance Lunar distances Relative speed
2027-01-20 05:26:00 Earth 0.1379 AU 53.7 LD 6.5 km/s
2027-07-14 03:27:00 Earth 0.2578 AU 100.3 LD 6.7 km/s
2031-01-10 13:42:00 Venus 0.0254 AU 9.9 LD 5.7 km/s
2033-02-27 17:45:00 Earth 0.0854 AU 33.2 LD 5.3 km/s
2051-04-08 19:29:00 Earth 0.1373 AU 53.4 LD 8.9 km/s
2056-01-22 07:52:00 Earth 0.4138 AU 161.0 LD 16.9 km/s
2056-09-09 22:26:00 Earth 0.2627 AU 102.2 LD 9 km/s
2057-04-07 04:39:00 Earth 0.2498 AU 97.2 LD 12.4 km/s
2061-10-23 01:44:00 Venus 0.0897 AU 34.9 LD 7.1 km/s
2062-01-17 10:52:00 Earth 0.2988 AU 116.3 LD 13.1 km/s

Next ten from today. 1 lunar distance = 384,400 km. Source: JPL close-approach data.

Sources