A lunar eclipse provides interesting viewing for everyone, from experienced observers to first-timers. Here at the Farmers’ Almanac, we are inviting our readers to make and share their observations of January’s “Blood Wolf Moon” total lunar eclipse, coming to your night sky January 20-21, 2019. See the timetable of this eclipse here.
Notice Anything Unusual?
No matter whether you plan to watch this lunar show for pleasure, or plan to make some planned observations, you should be on alert for any unusual happenings. In rare cases, the Earth’s shadow projected on the Moon can have a zigzag shape, or there can be an abnormal pattern of darkness inside the umbra. If skies are clear, this should be a very extensively observed lunar eclipse because of the favorable combination of a holiday weekend night (Monday is Martin Luther King, Jr. Day), and the fact that the eclipse is visible from coast to coast.
Coloration and Darkness
There is a wide range in the brightness of the Moon from one eclipse to another. Part of this difference comes from the Moon sometimes passing through the darkest part of the Earth’s shadow, at other times through the lighter outer umbra. But there is evidence of actual differences in the shadow from year to year, and thus a careful description of the colors seen on the totally eclipsed Moon and their changes is very valuable, especially by people with art experience.
Use The “Danjon Number” To Measure Eclipse Brightness
The hues depend on the optical equipment used, usually appearing more vivid with the naked eye than through telescopes. In the early 20th century the French astronomer André Danjon, introduced the following five-point scale of lunar luminosity (“L”) to classify eclipses:
L = 0: Very dark eclipse, the Moon is almost invisible, especially in mid-totality.
L = 1: Dark eclipse, the Moon has a gray or brownish coloration, details distinguishable only with difficulty.
L = 2: Deep red or rust-colored eclipse, with a very dark central part in the shadow, and outer edge of the umbra relatively bright.
L = 3: Brick red eclipse, usually with a bright or yellow rim to the shadow.
L = 4: Very bright copper-red or orange eclipse, with a bluish very bright shadow rim.
Estimates of this “Danjon number” form a long-standing record of lunar eclipse brightnesses so they are well worth continuing even in this age when brightness can be measured more precisely by photoelectric photometry. Visual estimates made by large numbers of people at the same time as photometric measures serve to calibrate decades of past observations.
You Be The Judge
To judge the Danjon number you can use your naked eye, binoculars, or a small telescope at low power. A fractional estimate, such as 1.8 or 2.5, may seem the most appropriate. Try to make three measurements: Examine the moon at mid-totality and also near the beginning and end of totality to get an impression of both the inner and outer umbra.
At mid-totality, the darkness of the sky is very impressive. Faint stars, which were completely washed out by the brilliant moonlight prior to the eclipse, become visible. The surrounding landscape takes on a somber hue. As totality ends, the eastern edge of the moon begins to emerge from the umbra, and the sequence of events repeats in reverse order until the spectacle is over.
Unless airborne volcanic aerosols or other unusual atmospheric effects influence its appearance, the Moon’s disk should appear moderately bright, especially right around the beginning and end of totality. The upper part of the Moon will likely appear brightest and glowing a ruddy or coppery hue, while the lower half of the moon should look more gray or chocolate in color.
Send Us Your Observations
We want you to participate! Send us your observations:
- Provide your name, location, and the Danjon Scale measurement (above).
- Provide the time that you made your observations.
- Indicate if you used just naked eye observation or if you use binoculars or a telescope.
Send your observations to: firstname.lastname@example.org.
After we get enough estimates, we’ll report on just how bright (or dark) the eclipse appeared to our readers in the coming weeks.
We look forward to hearing from you. Good luck and here’s wishing you clear skies!