The Earth will reach its aphelion today at 8 P.M. Eastern Daylight Time. This is the point in the planet’s elliptical orbit where it is farthest from the Sun.
Today, the Earth is about 152 million kilometers away from its nearest star. That is approximately 5 million kilometers further than during the perihelion in early January. The exact date of the aphelion differs from year to year, but it’s usually in early July.
While the planet’s distance from the Sun does not cause the seasons, it does influence their length. As a function of gravity, the closer the planet is to the Sun, the faster it moves. So, at the aphelion, the Earth will move more slowly along its orbital path than at any other time of the year. As a result, summer is elongated by a few days in the northern hemisphere.
The word, aphelion, is Greek for “away from sun”.
Image Credit: mydarksky.org
There is a saying, “A picture is worth a thousand words.” As Earth Week continues with events around the world to raise environmental awareness and encourage action on climate change, the photograph, Earthrise, seems to be the epitome of that old adage.
Orbiting the moon, William Anders, an astronaut onboard NASA’s Apollo 8 mission, captured the now historic image on December 24, 1968. Published in Life Magazine’s 100 Photographs that Changed the World edition, Galen Rowell – a prominent nature photographer of the time – famously called Earthrise, “the most influential environmental photograph ever taken.”
Although forty-six years have passed since this iconic image was captured on film, its subtle message seems more relevant than ever.
“Earthrise” Image Credit: William Anders/NASA
The Earth reached its Perihelion today at 12 UTC, which is 7AM Eastern Standard Time. This is the point in the planet’s orbit where it comes closest to the Sun.
This annual event is due to the elliptical shape of the Earth’s orbit and the off-centered position of the Sun inside that path. The exact date of the Perihelion differs from year to year, but it’s usually in early January – winter in the northern hemisphere. The Earth will be furthest from the Sun in July.
While the planet’s distance from the Sun is not responsible for the seasons, it does influence their length. As a function of gravity, the closer the planet is to the Sun, the faster it moves. Today, the Earth is about 146 million kilometers away from the Sun. That is approximately 5 million kilometers closer than in early July. This position allows the planet to speed up by about one-kilometer/second. As a result, winter in the northern hemisphere is about five days shorter than summer.
The word, perihelion, is Greek for “near sun”.
Image Credit: Academy Artworks
Today is the December Solstice, the first day of winter in the northern hemisphere. The new season officially began at 17:11 UTC, which is 12:11pm Eastern Standard Time.
The astronomical seasons are produced by the tilt of the Earth’s axis – a 23.5° angle – and the movement of the planet around the sun. During the winter months, the northern half of the Earth is tilted away from the sun. This position brings the hemisphere its least amount of solar energy and its coolest temperatures of the year.
Since the summer solstice in June, the arc of the sun’s daily passage across the sky has been dropping toward the southern horizon and daylight hours have been decreasing. Today, it reached its southern most position at the Tropic of Capricorn and marks the shortest day of the year. This observable stop is where today’s event takes its name. Solstice is derived from the Latin words “sol” for sun and “sisto” for stop.
Now, the sun will move northward again in our sky and daylight hours will slowly start to increase. Marking this transition, the winter solstice has long been a cause for celebration across many cultures throughout human history.
The tilt of the Earth during different seasons. Image Credit: NASA
Earth’s position on the Winter Solstice. Image Credit: NASA
Today is the Autumnal Equinox, the first day of fall in the northern hemisphere. The new season officially arrives at 20:44 UTC (4:44 PM EDT) when the sun is directly in line with the Earth’s equator.
Seasons are the result of the tilt of the Earth’s axis, a 23.5° angle. Today, as autumn begins, the planet’s axis is tilted neither toward nor away from the sun. As a result, we receive approximately equal hours of day and night. Derived from Latin, the word “equinox” literally means “equal night”.
As a transitional season, autumn is a time when the heat of summer fades away and the chill of winter gradually returns. The largest drop in average temperature, however, usually lags the equinox by a few weeks.
The angle of the sun’s rays hitting the Earth on the Autumnal Equinox.
Image Credit: Przemyslaw “Blueshade” Idzkiewicz
The government does not control the weather. It does, however, exercise significant power over scientists’ ability to produce reliable forecasts.
Sequestration, the current budget crisis plaguing Congress, threatens widespread automatic spending cuts for all federal agencies starting March 1st. The National Oceanic and Atmospheric Administration’s satellite program is one of many facing disruption. The agency’s current polar-orbiting weather satellite, Suomi NPP, is due to retire in 2016. Without funding to develop and launch a replacement, there will be a significant decline in the amount of data available for the computer models that are used to forecast the weather. Simply put, less data means less accurate forecasts. This will be especially important when meteorologists try to determine the path of future life threatening weather events like hurricanes and blizzards.
The sequestration is also expected to cut billions of dollars in federal aid to the victims of Hurricane Sandy and reduce FEMA’s ability to respond to future natural disasters.
Last month, NASA released Blue Marble 2012, a high-definition photograph of Earth taken from space.
The original Blue Marble was taken on December 7, 1972 by the astronauts of the Apollo 17 lunar mission. It was the first clear image taken of our entire planet. The famous photograph shows much of the eastern hemisphere and a cyclone in the Indian Ocean.
The new image highlights North America. It is a composite of numerous photos taken on January 4, 2012 by the Suomi NPP satellite. The remarkable clarity of the photograph is a product of the satellite’s onboard Visible /Infrared Imager Radiometer Suite (VIIRS) instrument.
This satellite is named in honor of the late Verner Suomi, a pioneer of satellite meteorology. It will gather data for enhanced weather forecasting and climate models.
Blue Marble 2012
Blue Marble 1972
Image Credit: NASA
On Monday night, the Aurora Borealis, also know as the Northern Lights, made a rare appearance in the lower latitudes of the US. These geomagnetic storms are normally limited to the polar regions, where the earth’s magnetic field is strongest.
An aurora is an optical phenomenon that is the result of charged solar particles becoming trapped in the Earth’s magnetic field. These particles ionize or excite the gases that make up our atmosphere. As these gases return to their ground state, they emit light energy that we see as neon-like colors dancing in the sky. The different colors can depend on the amount of energy absorbed, but in general, oxygen tends to produce a green light and nitrogen gives off a red glow.
Auroras at the poles are connected to the solar wind, a continuous flow of charged particles outward from the sun. Monday’s unusual display, however, was caused by an intense storm on the surface of the sun and coronal mass ejection. This tremendous eruption of solar wind temporarily allowed the auroral zone in our atmosphere to expand southward.
Auroral activity tends to be strongest around the seasonal equinoxes. In the southern hemisphere, auroras are called Southern Lights or Aurora Australis.
- Northern Lights
Photo credit: dakotalapse.com
It’s raining satellites! Well, at least parts of satellites. Over the weekend, an out-of-service NASA weather satellite broke apart and rained down on the Earth. Experts believe the space junk touched down in the Pacific Ocean, but cannot say where exactly. Luckily, no injures have been reported.
The source of this metallic precipitation was an Upper Atmosphere Research Satellite (UARS) that was launched in 1991 to study the chemical composition of the atmosphere and the amount of UV light coming from the sun. It was decommissioned in 2005.
It is rather poetically ironic that experts had a difficult time forecasting exactly when and where the weather satellite would fall. The best estimate was somewhere between 57 degrees north latitude and 57 degrees south latitude… a huge section of the planet … with a debris field some 500 miles long. The behavior of the falling satellite was uncontrolled and unpredictable. A fitting final tribute, I think, to the chaos inherent to the weather that the satellite monitored.
Image Credit: NASA