The total lunar eclipse of December 20–21, 2010 is a useful lesson in reading an eclipse prediction. Its coincidence with the December solstice made it memorable, but the observing task was the familiar one: identify the shadow phases, convert their times and check whether the Moon was above your horizon. Those same steps work for another lunar eclipse when you use that event's own circumstances.
Two shadows explain the sequence
A lunar eclipse occurs when the full Moon passes through Earth's shadow. The penumbra is the region where Earth blocks part of the Sun; the umbra is where Earth blocks the Sun's direct disk completely. A total eclipse has a period when the entire lunar disk lies inside the umbra. Earth's atmosphere still redirects some sunlight toward it, often producing copper or red colors.
NASA's eclipse explanation connects these stages to the Moon's tilted orbit. Full moons usually pass above or below the shadow. The solstice describes Earth's seasonal orientation; the eclipse requires a separate alignment near the crossing of the lunar orbital plane and Earth's orbital plane. A solstice alone does not produce an eclipse.
Read the December 2010 contacts
The following times come from NASA's 2010 eclipse circumstances. They are historical predictions in Universal Time (UT), rounded here to the nearest minute for an observing exercise. The Eastern Standard Time conversion subtracts five hours. These times apply to December 21, 2010.
| Contact | What begins or ends | UT | EST |
|---|---|---|---|
| P1 | First entry into the penumbra | 05:29 | 00:29 |
| U1 | Partial umbral eclipse begins | 06:33 | 01:33 |
| U2 | Totality begins | 07:41 | 02:41 |
| Greatest | Closest approach to the shadow axis | 08:17 | 03:17 |
| U3 | Totality ends | 08:53 | 03:53 |
| U4 | Partial umbral eclipse ends | 10:01 | 05:01 |
| P4 | Final exit from the penumbra | 11:05 | 06:05 |
Using the unrounded source times, totality lasted about 72 minutes, the U1–U4 interval about 3 hours 29 minutes, and the P1–P4 interval about 5 hours 35 minutes. A duration becomes useful only when its endpoints are named. The earliest and latest penumbral shading can be hard to notice even with a clear view.
Turn a global prediction into a local plan
- Choose the correct event. Start with NASA's lunar-eclipse resources and open the event's map and circumstances. Save the source and time standard.
- Convert the full sequence. Apply your location's UTC offset for that date, including daylight-saving rules. UT and UTC differences are immaterial to this minute-rounded historical exercise, but retain the stated standard in precise work.
- Check the horizon. Use a planetarium or location-specific ephemeris for Moon altitude, direction, moonrise and moonset. A contact time can occur while the Moon is below your horizon.
- Inspect the site. Buildings, trees, hills, twilight and cloud cover determine what your local view permits. Favor a clear view in the Moon's direction during the phases you want.
- Record what you actually see. Note time, phase, color, cloud and equipment together. Begin with naked-eye observations; binoculars reveal changes across the lunar face.
The lunar-eclipse planning note keeps predicted contacts separate from your observations. It includes the historical conversion example and blank fields for another event.
Make comparisons that preserve context
Photographic brightness depends on exposure as well as the eclipsed Moon. For a sequence, record shutter time, aperture and sensitivity; a camera in automatic mode may brighten totality and hide the actual change. Compare similar settings or clearly annotate adjustments.
Atmospheric conditions along the sunlight's path through Earth's limb influence eclipse color. Local haze and camera processing add further effects. Describe the observed color first, then use supporting atmospheric information before assigning a cause. For identifying the terrain beneath the changing illumination, use the lunar terrain guide.