Three Supermoons in a Row

July 10, 2014: In June of last year, a full Moon made headlines.  The news media called it a "supermoon" because it was 14% bigger and 30% brighter than other full Moons of 2013.   Around the world, people went outside to marvel at its luminosity.

If you thought one supermoon was bright, how about three….? The full Moons of summer 2014—July 12th, August 10th, and Sept. 9th--will all be supermoons.

A new ScienceCast video counts the supermoons of summer 2014. Play it

The scientific term for the phenomenon is "perigee moon." Full Moons vary in size because of the oval shape of the Moon's orbit. The Moon follows an elliptical path around Earth with one side ("perigee") about 50,000 km closer than the other ("apogee").  Full Moons that occur on the perigee side of the Moon's orbit seem extra big and bright.

This coincidence happens three times in 2014.  On July 12th and Sept 9th the Moon becomes full on the same day as perigee.  On August 10th it becomes full during the same hour as perigee—arguably making it an extra-super Moon."

It might seem that such a sequence must be rare.  Not so, says Geoff Chester of the US Naval Observatory.
"Generally speaking, full Moons occur near perigee every 13 months and 18 days, so it's not all that unusual," he says. "In fact, just last year there were three perigee Moons in a row, but only one was widely reported."

In practice, it's not always easy to tell the difference between a supermoon and an ordinary full Moon. A 30% difference in brightness can easily be masked by clouds and haze.  Also, there are no rulers floating in the sky to measure lunar diameters. Hanging high overhead with no reference points to provide a sense of scale, one full Moon looks about the same size as any other.

Chester expects most reports of giant Moons this summer to be … illusory.

“The ‘Moon Illusion’  is probably what will make people remember this coming set of Full Moons, more than the actual view of the Moon itself,” he says.

The illusion occurs when the Moon is near the horizon.  For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings and other foreground objects. When the Moon illusion amplifies a perigee Moon, the swollen orb rising in the east at sunset can seem super indeed.

"I guarantee that some folks will think it's the biggest Moon they've ever seen if they catch it rising over a distant horizon, because the media will have told them to pay attention to this particular one," says Chester.
"There's a part of me that wishes that this 'super-Moon' moniker would just dry up and blow away, like the 'Blood-Moon' that accompanied the most recent lunar eclipse, because it tends to promulgate a lot of mis-information," admits Chester. "However, if it gets people out and looking at the night sky and maybe hooks them into astronomy, then it's a good thing."

Indeed it is.

Mark your calendar--July 12th, August 10th, and Sept. 9th –and enjoy the super-moonlight.

Credits:

Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit: Science@NASA

The Gateway to Astronaut Photography of Earth - Live HD Feed from the ISS

Live HD Earth viewing from the International space station! Sit back, watch & enjoy our home planet.
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View link: http://eol.jsc.nasa.gov/HDEV/ 

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Rain and Snow Satellite Set to Launch

Feb. 26, 2014:  As Arthur C. Clarke once remarked, "How inappropriate to call this planet Earth when it is quite clearly Ocean."

Indeed, Earth is a water world.  The dry land most of us call home covers less than a third of the planet’s surface.  Water moves around Earth with a circulation as complex as that of the human body. Evaporation, condensation, and precipitation transport warmth and moisture from place to place, sustaining life and setting the stage for weather and climate.

"The water-cycle, so familiar to all school-age young scientists, is one of the most dynamic and important elements in our studies of Earth," says John Grunsfeld, associate administrator for NASA's Science Mission Directorate in Washington DC.  "We're about to launch a new satellite that gives us critical information about how the water-cycle works."

A new ScienceCast video, "Follow the Water," previews the mission of the Global Precipitation Measurement Core Observatory. Play it

 

It's called the Global Precipitation Measurement Core Observatory--or "GPM" for short. Built by NASA and JAXA, the Japan Aerospace Exploration Agency, the satellite is scheduled to launch on Feb. 27th at 1 pm EST from the Tanegashima Space Center in Japan.

GPM will fly 253 miles above Earth in an orbit inclined 65-degrees to the equator. This orbit allows the satellite to monitor precipitation all the way from the Arctic to the Antarctic circles. Working with a network of other satellites--some already in orbit and some planned for the future--GPM can measure rain and snow every three hours anywhere on the globe.

"The kind of data we'll get from the GPM network is unprecedented," says Gail Skofronick-Jackson, GPM project scientist at Goddard. "We'll be able to observe detailed characteristics of rain and snow systems that are extremely important for improving weather and climate forecasts."

Normal operations will begin about 60 days after launch.  Data will be downlinked through NASA's Tracking and Data Relay Satellite System to NASA's Precipitation Processing Center in Greenbelt, Md., where it will be processed and distributed over the Internet.

GPM carries two instruments to measure rain and snowfall: a Dual-frequency Precipitation Radar and the GPM Microwave Imager. Compared to instruments flown on previous Earth science satellites, GPM’s precipitation radar and microwave imager can see deeper into clouds and detect smaller particles of rain, ice and snow. The radar will be able to form 3D profiles of precipitation, revealing the inner workings of cloudy storm systems.  The microwave imager will measure not only heavy and moderate rain, as other satellites do, but also light rain and snow—two forms of precipitation important over mountain ranges and high-latitude sites in North America, Europe and Asia.

What we learn from GPM network, concludes Grunsfeld, "will help us cope with future extreme weather events and manage fresh water resources" in a changing world.

Make that water world.

Credits:

Author: Dr. Tony Phillips | Production editor: Dr. Tony Phillips | Credit: Science@NASA