Tag Archives: seasons

Today is Earth’s Perihelion

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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

Image Credit: Academy Artworks

Winter Solstice 2013

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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

The tilt of the Earth during different seasons.  Image Credit: NASA

winter_solstice-1

Earth’s position on the Winter Solstice.  Image Credit: NASA

Autumnal Equinox 2013

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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.

Autumnal Equinox. Image Credit: Image Credit: Przemyslaw “Blueshade” Idzkiewicz

The angle of the sun’s rays hitting the Earth on the Autumnal Equinox.

Image Credit: Przemyslaw “Blueshade” Idzkiewicz

Summer Solstice 2013

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Today is the June Solstice, the first day of summer in the northern hemisphere. The new season officially began at 5:04 UTC, which is 1:04 Eastern Daylight Time.

Astronomical seasons are the result of the tilt of the Earth’s axis, a 23.5° angle. Today, as summer begins, the northern half of our planet is slanted toward the sun.  This position allows the northern hemisphere to receive the sun’s energy at a more direct angle, warming the entire region.

The summer solstice is often called the “longest day of the year”.  This, however, is a bit of a misnomer as one day always contains twenty-four hours.  Nonetheless, today is the day with the longest duration of daylight. Since the winter solstice in December, the sun – in its apparent seasonal journey across the sky – has been making its way north. Reaching its northern-most position at the Tropic of Cancer today, it stopped.  This phenomenon is where today’s event takes its name. Solstice is a word derived from Latin meaning, “sun stands still”.

SeasonsImage Credit: NASA

Vernal Equinox 2013

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Today is the Vernal Equinox, the first day of spring in the northern hemisphere. The new astronomical season officially began at 11:02 UTC, which is 7:02 A.M. Eastern Daylight Time.

Seasons are the result of the tilt of the Earth’s axis, a 23.5° angle. Today, as spring begins, the Earth’s axis is tilted neither toward nor away from the sun. As a result, we receive approximately equal hours of day and night.

The spring equinox usually marks the end of winter’s chill and the gradual return of warmth.  This year, however, many people across the U.S. are experiencing conditions that feel more like the Dead of Winter.  These unseasonably cool temperatures are expected to remain in place for the near future as the polar jet stream continues to dip south over a large portion of the country.

A frosty start to spring in NYC

A frosty start to spring in NYC

Image Credit: The Weather Gamut

Winter Solstice 2012

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Today is the December Solstice, the first day of winter in the northern hemisphere. The new season officially began this morning at 6:12 AM Eastern Standard Time.

Seasons are the result of the tilt of the Earth’s axis, a 23.5° angle. Today, as winter begins, the northern half of the Earth is tilted away from the sun. This position brings the northern hemisphere the least amount of solar energy all year.

Today is also the shortest day of the year.  Since the summer solstice in June, the sun – in its apparent seasonal journey across the sky – has been making its way south.  Today, it reached its southern most position at the Tropic of Capricorn.  Now, the sun will begin to move northward again and our daylight hours will slowly start to increase.

Marking the transition to longer days, the winter solstice has been a cause for celebration across many cultures throughout human history.

winter_solstice-1

Winter Solstice

Image Credit:scijink.nasa.gov

First Taste of Fall in NYC

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Autumn’s chill arrived in New York City this weekend, two weeks after the official start of the season.

Following days of above average warmth, temperatures dropped dramatically overnight on Saturday when a cold front moved through the region. This arctic blast brought the city its coldest air of the season to date.  Daytime highs plummeted from 78°F on Friday to 54°F on Sunday.

This jarring cold snap is a reminder that what goes up must come down, especially in a transitional season like autumn.  Forecasters expect to see a rebound in temperatures later this week, but only to seasonal levels.

Graph Credit: The Weather Gamut

Autumnal Equinox

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Today is the Autumnal Equinox, the first day of fall in the northern hemisphere. The new season officially arrives at 14:49 UTC (10:49 A.M. Eastern Daylight Time).

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. In fact, the word “equinox” is Latin for “equal night”.

As a transitional season, autumn is a time when the heat of summer fades away and winter’s chill gradually returns. The largest drop in average temperature, however, usually lags the equinox by a few weeks.

Autumnal Equinox

Image Credit: Przemyslaw “Blueshade” Idzkiewicz

Aphelion

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The Earth will reach its aphelion today at 11 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.

The planet’s distance from the Sun does not cause the seasons, but 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: astronomy.edu.au

Summer Solstice

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Today is the June Solstice, the first day of summer in the northern hemisphere. The new season officially begins at 23:09 UTC, which is 7:09 PM Eastern Daylight Time.

Astronomical seasons are the result of the tilt of the Earth’s axis, a 23.5° angle. Today, as summer begins, the northern half of our planet is slanted toward the sun.  This position allows the northern hemisphere to receive the sun’s energy at a more direct angle, warming the region.

Today is also the longest day of the year. Since the winter solstice in December, the arc of the sun’s daily passage across the sky has been moving northward.   Reaching its northern-most position at the Tropic of Cancer today, it stopped.  This phenomenon is where today’s event takes its name – solstice is a word derived from Latin meaning, “sun stand still”.

Beginning tomorrow, the sun will embark on its apparent journey southward and our daylight hours will slowly decrease.

Summer Solstice in Northern Hemisphere

Image Credit: scijink.nasa.gov