"Opposition longitude" (in degrees) is exactly opposite to the direction of the Sun through Earth's center. Asteroids in this region, near the ecliptic and outside Earth's orbit, are at their brightest as seen from Earth and thus most likely to be discovered and followed. Objects come and go, showing in the viewer only while inside ten LD or under active observation (and leave trails only when inside 20 LD).
Viewer frame rate seems smoothest at the "good" speed setting, but your experience may differ. Single-clicking anywhere on the skychart acts like hitting the [Run] button.
This Asteroid/Comet Connection (A/CC) animated illustration runs in HTML5 using data from NASA/JPL Horizons (see credits) and the Bright Star Catalog, with star colors per Mitchell Charity. We welcome feedback.
Object Details - skychart objects presented in reverse designation order, newest first
("designation assigned to" indicates unofficial discovery credit)
1. Ten lunar distances: One "lunar distance" (LD) is the average distance between Earth and Moon (about 384,400 km., the same as 238,855 miles or 9.59 times around Earth's equator). Ten lunar distances has no special astronomical importance but is a useful giant traveling "bubble" within which to organize this special reporting. The approach of a small Solar-System body becomes more interesting when it nears or comes closer than 2.41 LD, as it encounters our planet's gravitational sphere of influence (SOI). Earth's gravity can change the orbits of objects passing through its SOI. The Moon also has its own SOI, which changes as its distance from Earth varies, but never extends much more than 0.18 LD. (The simple illustration above, with Earth and Moon not to scale, shows the Earth SOI as a dotted vertical blue line.) The "Earth-Moon system" is generally defined as that region of space within a radius of one lunar distance from Earth, so an object can pass quite close to the Moon yet not be described as coming "inside" the E-M system.
2. Data credit: All data on this page derived from orbit solutions comes from the NASA JPL Solar System Dynamics (SSD) Group through its Horizons system. All information about optical observations comes from the IAU Minor Planet Center (MPC) and info about radar observations comes from JPL SSD. The MPC, NASA, and JPL are not associated with this page or A/CC, and responsibility for the interpretation of this information and its use here rests entirely with A/CC. Important note: Approach times presented here as to-the-minute may have unstated uncertainties of a few minutes, or many minutes or even hours for objects with old or very short observation spans, which is significant because the Earth moves through its own diameter in about seven minutes. Thus actual encounter distances may vary, occasionally by as much as ten lunar distances. See JPL's Close Approach Tables for nominal vs. minimum possible passage distances and times, and for their note about uncertainties.
3. Size estimates: Object diameters are rough approximations derived by standard formula from H, an object's "absolute magnitude" (brightness), where higher numbers represent dimmer (thus usually smaller) objects.
4. Skychart further notes: For illustrative purposes, the Sun and Moon are shown way out of proportion to the background sky, each depicted as five degrees in apparent diameter instead of about a half degree actual. All asteroids as tracked from Earth are single points of light without an apparent diameter.
5. Skychart known issues: