10:30 AM | Why the recent lunar eclipse was so dark

[Image of the relatively dark moon taken in Massachusetts during totality of the recent eclipse]

Discussion

Overview

On September 27th, the moon passed through the shadow of Earth and the total lunar eclipse was witnessed by millions around the world. Most people agreed that the lunar eclipse was darker than usual (example image above) – not the often seen bright orange or red. Believe it or not, the darker appearance to the moon during the total eclipse was actually due in large part to a volcanic eruption that took place in Chile months earlier.

Volcanic dust in the stratosphere

Chile’s Calbuco volcano erupted in April 2015 and six months later we are still seeing the effects of the volcanic aerosols (ash, dust, sulfuric acid droplets) that reached the lower stratosphere. Sunsets in both hemispheres have been more colorful than normal from the upper atmosphere volcanic aerosols and it appears to have affected the eclipse as well.

When the stratosphere is full of volcanic ash and other aerosols, lunar eclipses then to be dark red whereas when stratospheric conditions are relatively clear, lunar eclipses can be bright orange. Sunlight has to pass through these light-absorbing minerals and chemicals on its way through the atmosphere and into Earth’s shadow. Less light means a darker moon during total eclipse. The eclipse of September 27th was measured by trained observers at 0.4 magnitude dimmer than expected, a brightness reduction of around 33 percent (plot below).

[Predicted lunar eclipse brightness; courtesy Dr. Keen, University of Colorado]

Volcanic dust in the atmosphere also acts to cool the Earth below by reflecting sunlight. This particular volcanic eruption actually created a very small amount of cooling on Earth; however, there have been past eruptions resulting in more significant cooling around the world. For example, the eruption of Pinatubo in 1991 produced much more cooling than Calbuco and it resulted in rare July snows across higher elevations of the US Rocky Mountains.

Other possible contributing factor

Forest fires that raged across the western states and Canadian provinces all spring and summer may also have contributed to the darker than normal appearance of the moon during the recent eclipse. Most of that wildfire smoke usually stays in the lower part of the atmosphere, but some may have found its way to the stratosphere, the very layer responsible for transmitting most of the sunlight that falls into Earth’s shadow and colors the moon.

9:15 AM | NASA/Wallops launch tonight should be visible here..."glowing" clouds to be generated right after launch should also be visible

[These "glowing" clouds were produced by five suborbital NASA rockets that launched on March 27, 2012, from the agency's Wallops Flight Facility in Virginia; courtesy NASA]

Discussion

A launch is planned for ~7pm tonight at the NASA/Wallops facility and it should be visible in much of the Mid-Atlantic region depending on local weather conditions (which look pretty favorable). In addition, one of the main purposes of the mission is to generate “glowing clouds” high above the Earth which should also be visible in the region shortly after launch.

The main goal of Wednesday's launch is to test the performance of the two-stage Black Brant IX sounding rocket, which will be flying with a reformulated motor, NASA officials said. But the mission also serves to try out a number of technologies including newly developed lightweight materials and novel payload-ejection systems. The rocket will be launched on an east-southeast trajectory, reaching a maximum altitude (apogee) of 161 miles (259 kilometers) about 4.5 minutes after it leaves the launch pad at Wallops.

[Rocket launch at NASA/Wallops from earlier this year; courtesy NASA]

Another purpose of this mission is to generate “glowing clouds” which will be used to study wind in space and the ionosphere. About 6 to 6.5 minutes after the launch, on the rocket's downward leg, as many as four barium clouds will be released over the Atlantic Ocean, at altitudes of between 118 and 130 miles (190 to 209 km), over a point roughly 125 miles (200 km) downrange from Wallops. Scientists have launched vapor tracers into the upper atmosphere since the 1950s. Such research has greatly aided understanding of the planet's near-space environment.

Vapor clouds seemingly explode into view when first released, sometimes blooming so rapidly they resemble fuzzy fireworks. Depending on the state of the atmosphere, these clouds may appear to expand to several times the apparent size of the moon; on other occasions, they appear to elongate in a north-south fashion or stretch out into long plumes. Initially, they may appear to glow with prismatic colors, although the primary colors are expected to trend toward bluish-green and purple-red. Since observers must be in darkness while the barium cloud is in sunlight, the technique is limited to observations near sunset, local time. Depending on atmospheric conditions, the barium clouds could persist for as little as 2 minutes or they could linger for as long as 20 minutes before fading away.

To find the exact launch time and to watch the launch live go here: http://www.ustream.tv/channel/nasa-tv-wallops. In the Philly and DC metro regions look near the horizon towards the south and then to the southeast; in the DC metro region look near the horizon towards the southeast and then to the east.

[This map shows areas where tonight's sounding rocket launch may be visible; courtesy NASA]