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Public Universe
Asteroid Near-Earth

2021 BC

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(2021 BC)

Where is it now

Distance from Sun
0.82 AU
True anomaly
133.88°
Distance from Earth
0.688 AU
As of
15 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 — 0.997 AU from the Sun Earth 2021 BC — 0.82 AU from the Sun 2021 BC
Seen from above the ecliptic, north up, to scale. Grid: Earth's orbit in blue. 2021 BC is 0.688 AU from Earth today (5.7 light-minutes).

In the sky

Right ascension
10h 49m 07s
Declination
+31° 17′ 29″
Constellation
Leo Minor
Distance from Earth
0.69 AU
Elongation from the Sun
55.03° — near the Sun — look low at dusk or dawn

Favours the northern hemisphere; low or below the horizon from far south.

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
0.706 AU
Eccentricity
0.4347
Inclination
21.25°
Orbital period
216.7 days
Perihelion
0.399 AU
Aphelion
1.013 AU
Longitude of ascending node
300.48°
Argument of periapsis
346°
Epoch · J2000
2461200.5
Orbit class · ATE
Aten
Earth MOID · 2.1 LD
0.0055 AU
Tisserand (Jupiter)
7.988

Orbit quality

Orbit poorly determined (uncertainty code 7).

Observations used
59
Data arc
16 days
First observed
6 January 2021
Last observed
22 January 2021
Residual RMS
0.41 ″
Solution · Otto Matic
15 April 2021

Physical properties

Rotation period
0.33 hours

Visual & observation

Absolute magnitude (H)
24.3

Discovery & classification

Aten Near-Earth Object

Close approaches 143 on record

Flyby geometry
Ecliptic flyby of 2021 BC at 2027-01-20 12:18 UTC Top-down view of the ecliptic, Earth at the centre, for the 2027-01-20 12:18 UTC close approach of 2021 BC. Catalogue miss distance 131.8 LD · 5.07 × 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 south of the ecliptic. The path is a geocentric ecliptic ephemeris from JPL Horizons. The inset is a heliocentric view and is approximate. Sun 131.8 LD · 5.07 × 10⁷ km 2027-01-20 12:18 UTC Earth Moon Heliocentric, approximate

Top-down view of the ecliptic, Earth at the centre, for the 2027-01-20 12:18 UTC close approach of 2021 BC. Catalogue miss distance 131.8 LD · 5.07 × 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 south 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 12:18:00 Earth 0.3386 AU 131.8 LD 22.2 km/s
2030-12-30 06:39:00 Earth 0.3542 AU 137.8 LD 19.2 km/s
2033-10-07 14:28:00 Merc 0.0689 AU 26.8 LD 28.3 km/s
2033-10-07 14:28:00 Mercury 0.0689 AU 26.8 LD 28.3 km/s
2034-01-02 10:35:00 Earth 0.2131 AU 82.9 LD 14.3 km/s
2034-12-09 17:28:00 Merc 0.081 AU 31.5 LD 26.1 km/s
2034-12-09 17:28:00 Mercury 0.081 AU 31.5 LD 26.1 km/s
2037-01-14 04:27:00 Earth 0.0896 AU 34.9 LD 12.4 km/s
2040-01-23 20:49:00 Earth 0.0533 AU 20.7 LD 13.9 km/s
2042-08-29 20:01:00 Mercury 0.0561 AU 21.8 LD 26 km/s

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

Sources