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Asteroid Near-Earth Potentially hazardous

Zephyr

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12923 Zephyr (1999 GK4)

Where is it now

Distance from Sun
1.734 AU
True anomaly
253.06°
Distance from Earth
2.722 AU
As of
11 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.

Orbit of Mercury Orbit of Venus Orbit of Mars Sun Earth — 0.998 AU from the Sun Earth Zephyr — 1.734 AU from the Sun Zephyr
Seen from above the ecliptic, north up, to scale. Grid: Earth's orbit in blue. Zephyr is 2.722 AU from Earth today (22.6 light-minutes).

In the sky

Right ascension
13h 35m 55s
Declination
-07° 38′ 15″
Constellation
Virgo
Distance from Earth
2.72 AU
Elongation from the Sun
6.39° — too close to the Sun to observe

Visible from both hemispheres.

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
1.962 AU
Eccentricity
0.4931
Inclination
5.31°
Orbital period
2.75 years
Perihelion
0.994 AU
Aphelion
2.929 AU
Longitude of ascending node
168.07°
Argument of periapsis
147.23°
Epoch · J2000
2461200.5
Orbit class · APO
Apollo
Earth MOID · 7.6 LD
0.0196 AU
Tisserand (Jupiter)
3.716

Orbit quality

Orbit very well determined (uncertainty code 0).

Observations used
3,011
Data arc
70.99 years
First observed
21 April 1955
Last observed
18 April 2026
Residual RMS
0.41 ″
Solution · Otto Matic
27 June 2026

Physical properties

Mean radius
1.03 km
Rotation period
3.89 hours

Visual & observation

Geometric albedo
0.199
Absolute magnitude (H)
15.8
Spectral type (SMASS)
S:

Discovery & classification

Discovered by
LONEOS
Discovery date
11 April 1999
Discovery site
Anderson Mesa

The word zephyr derives from the name of the ancient Greek god of the west wind, Zephyros. The name was suggested by M. Smitherman.

Also known as 12923 · 1999 GK4

Apollo Near-Earth Object Named Potentially Hazardous Asteroid

Close approaches 2 on record

Flyby geometry
Ecliptic flyby of Zephyr at 2032-09-22 21:13 UTC Top-down view of the ecliptic, Earth at the centre, for the 2032-09-22 21:13 UTC close approach of Zephyr. Catalogue miss distance 72.4 LD · 2.78 × 10⁷ km. The curve is the geocentric path from 2032-09-19 to 2032-09-25, 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. The path is a geocentric ecliptic ephemeris from JPL Horizons. The inset is a heliocentric view and is approximate. Sun 72.4 LD · 2.78 × 10⁷ km 2032-09-22 21:13 UTC Earth Moon Heliocentric, approximate

Top-down view of the ecliptic, Earth at the centre, for the 2032-09-22 21:13 UTC close approach of Zephyr. Catalogue miss distance 72.4 LD · 2.78 × 10⁷ km. The curve is the geocentric path from 2032-09-19 to 2032-09-25, 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. 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
2032-09-22 21:13:00 Earth 0.186 AU 72.4 LD 13.8 km/s
2178-06-24 18:32:00 Earth 0.1959 AU 76.2 LD 13 km/s

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

Sources