Hey, Who Let the Air out of the Moon?!
You can thank atmospheric refraction for this droll little optical illusion.
In this image from August of 2016, sunlight reflected off of the Moon’s surface is bent as it passes through Earth’s atmosphere. By the time it arrives at the camera lens peering through the space station’s cupola window, something’s off.
Misshapen, yes. Permanent, no. Light travels fastest through a vacuum, slower through a medium – like air, for example. Where the atmosphere is denser its velocity is somewhat slower, and the light is bent, or refracted. Atmospheric refraction displaces stars from their expected location and warps the shape of larger objects like the Sun and Moon. These ‘altered states’ are most noticeable just above the horizon, where the atmosphere is densest.
Previous Image of the Week resources
November 11- November 15, 2017
Best. Lightshow. Ever.
Don’t book a room anywhere near Santa’s workshop if your goal is to observe the northern lights overhead. The aurora usually appear as a ring around the earth’s magnetic poles, called an auroral oval, with a diameter of about 2,500 miles. Consider a visit to Alaska, Denmark, or Iceland if it’s straight-up amazing light shows you’re looking for.
The crew of the International Space Station was passing over Mongolia, looking north toward Russia, when this image was taken. Notice the relative positions of the yellowish line that marks the edge of earth’s atmosphere, and the vivid green auroral display. What does this tell us about where in the atmosphere the aurora form?
November 4 - November 10, 2017
Mount Etna – It’s Alive!
Dual vents on Europe’s largest active volcano send plumes of steam in the direction of Riposto, a town along the eastern coast of Sicily. Mount Etna sits above a geologic hotspot, where the African plate subducts beneath the Eurasian plate. The active, 10,922-foot stratovolcano is about 500,000 years old. This image dates from August, 2014.
In 2013 Mount Etna was declared a UNESCO World Heritage site, largely for its “exceptional level of volcanic activity”. In spite of the hazards, about a quarter of the island’s population lives in the volcano’s immediate vicinity. And why wouldn’t they – thanks to Etna the soil is rich and fertile, vineyards and olive groves abound, and tourists spend money with considerable enthusiasm.
The moral of this story – if life gives you lava, make a Mediterranean paradise.
October 28 - November 3, 2017
“You’re old, dusty, gassy and warped. But beautiful. “
Scott Kelly’s words say a lot. He snapped this evocative image of our galactic hometown through the space station’s cupola window in September of 2015. Framed here by the humble forgings of mankind and the elegant arch of earth’s atmosphere, the sheer abundance of solar systems with which we share the neighborhood is breathtakingly apparent.
The fairly long exposure time required for this image – five seconds – accounts for the elongation of the stars, which would otherwise appear as sharp pinpoints of light. Temperature differences produce the wide range of colors seen here, from cooler red stars to hotter blue stars. Our yellowish sun is in the low to mid-range of this scale.
October 20 - 26, 2017
London After Dark
We love our electric lights. In fact, if you want to get a good sense of the population density of any first-world city, just wait for the sun to go down. 8.7 million people inhabit Greater London, and as this image from January of 2017 clearly illustrates, they all own at least one high-intensity light bulb.
Star gazing in these conditions can be frustrating or even impossible, thanks to a phenomenon known as skyglow. Light scattered by the atmosphere above our cities serves as a perpetual night light. Sleep deprivation induced by this relentless exposure has become a significant public health problem in many urban areas.
A grassroots effort known as the dark-sky movement works to raise awareness of, if not shed new light on, the impact of light pollution on people and wildlife.
October 13 - 19, 2017
Great American Eclipse
Our moon is 400-times smaller than our Sun, which the Earth and Moon orbit together. In a purely coincidental fact of celestial geometry, our moon is also 400-times CLOSER to the Earth than is the Sun. Every now and then the tilted orbital planes of the Earth and Moon intersect during a new moon, and the Moon’s elliptical orbit places it at just the right distance. Thus, from our perspective here on Earth, the Moon is centered in front of the Sun at a moment when their apparent sizes are the same. Thank you, 400.
October 6 - 12, 2017
Harvey Approaches the Coast of Texas
“Imagine being on a spaceship, watching this storm barreling down on your family. Fingers crossed for the Gulf Coast.”
Former ISS astronaut Chris Hadfield was referencing the fact that Johnson Space Center in Houston, TX is home to the astronaut corps, as well as their families, when he tweeted these words on August 24, 2017. This image was taken as the ISS flew over Hurricane Harvey prior to landfall on Friday, August 25 at 1:16 PM.
The massive storm came ashore just east of Corpus Christi, TX on Friday night as a Category 4 hurricane. It progressed very slowly once over land, meandering in the direction of San Antonio before heading back into the Gulf of Mexico, northeast to Houston, and eventually into Louisiana. The result was unrelenting rainfall for days, and widespread devastation due to flooding.