Tag Archives: seasons

Earth’s Perihelion 2016

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The Earth will reach its Perihelion today at 22:49 UTC, which is 5:49 PM 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 147.1 million kilometers (91.4 million miles) away from the Sun. That is approximately 5 million kilometers (3 million miles) closer than it will be 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”.

Earth's Perihelion and Aphelion. Credit: Time and Date.com

Earth’s Perihelion and Aphelion. Credit: TimeandDate.com

Winter Solstice 2015

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The December solstice – the first day of winter in the northern hemisphere – is upon us. The new season officially begins at 04:48 UTC on December 22nd, which is 11:48 PM EST tonight.

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 means the northern hemisphere receives the sun’s energy at a less direct angle and brings us our coolest temperatures of the year.

Since the summer solstice in June, the arc of the sun’s apparent daily passage across the sky has been dropping toward the southern horizon and daylight hours have been decreasing. Today, it will reach its southern most position at the Tropic of Capricorn (23.5° south latitude) marking 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.

Starting tomorrow, the sun will appear to move northward again and daylight hours will slowly start to increase. Marking this transition from darkness to light, the winter solstice has long been a cause for celebration across many cultures throughout human history.

Earth’s solstices and equinoxes. Image Credit: NASA

Earth’s solstices and equinoxes. Image Credit: NASA

Autumnal Equinox 2015

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Today is the Autumnal Equinox, the first day of fall in the northern hemisphere. The new season officially began at 8:21 UTC, which is 4:21 AM Eastern Daylight Time.

The astronomical seasons are a product of the tilt of the Earth’s axis – a 23.5° angle – and the movement of the planet around the sun. During the autumn months, the Earth’s axis is tilted neither toward nor away from the sun. This position distributes the sun’s energy equally between the northern and southern hemispheres.

Since the summer solstice in June, the arc of the sun’s apparent daily passage across our sky has been moving southward and daylight hours have been decreasing. Today, it crossed the equator and we have approximately equal hours of day and night. The word “equinox” is derived from Latin and means “equal night”.

With the sun sitting lower in the sky and daylight hours continuing to shorten, Autumn is a season of falling temperatures.  According to NOAA, the average high temperature in most US cities drops about 10°F between September and October.

Solstices and Equinoxes. Credit: NASA

Earth’s solstices and equinoxes. Image Credit: NASA

Equinox

The Earth’s axis is tilted neither toward nor away from the sun on the Equinox. Image Credit: NASA

Earth’s Aphelion 2015

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The Earth will reach its Aphelion today at 19:41 UTC, which is 3:41 PM Eastern Daylight Time. This is the point in the planet’s orbit where it is farthest from the Sun.

This annual event is a result of the elliptical shape of the Earth’s orbit and the off-centered position of the Sun inside that path. The exact date of the Aphelion differs from year to year, but it’s usually in early July – summer in the northern hemisphere.

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, Earth is about 152 million kilometers (94 million miles) away from the Sun. That is approximately 5 million kilometers (3 million miles) further than during the perihelion in early January. That means the planet 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

Image Credit: mydarksky.org

Seasonal Temperature Lag

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The June Solstice marks the official beginning of the summer season in the northern hemisphere. It is famous as the longest day of the year – a day when we receive the greatest amount of incoming solar radiation. The reason it is not also the warmest day of the year relates to a phenomenon known as seasonal temperature lag.

Air temperature depends not only the amount of energy we receive from the sun, but also the amount of energy absorbed by the planet’s landmasses and oceans. The heat capacity of both, which is defined as the amount of heat required to raise the temperature of a substance 1°C, play a major role. Given the fact that water has a much higher heat capacity than land and that oceans cover 71% of the Earth’s surface, it takes awhile for the atmosphere to warm up. Here in the mid- latitudes, we usually see our warmest days of the year in mid-July which are often referred to as the Dog Days of Summer.

In winter, the process works in reverse. The oceans take time to lose their heat. So, the coldest days generally lag the winter solstice by a few weeks.

Summer Solstice 2015

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Today is the June Solstice, the first day of summer in the northern hemisphere. The new season officially begins at 16:38 UTC, which is 12:38 PM Eastern Daylight 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 summer months, the northern half of the Earth is angled toward the sun. This position allows the northern hemisphere to receive the sun’s energy at a more direct angle and produces our warmest temperatures of the year.

Since the winter solstice in December, the arc of the sun’s apparent daily passage across the sky has been moving northward and daylight hours have been increasing. Today, it reached its northern most position at the Tropic of Cancer (23.5° north latitude) marking the “longest day” of the year. This observable stop is where today’s event takes its name. Solstice is a word derived from Latin meaning, “sun stands still”.

Now, the sun will start to move southward again in our sky and daylight hours will slowly decrease.

Earth’s solstices and equinoxes. Image Credit: NASA

Earth’s solstices and equinoxes. Image Credit: NASA

The Sun is directly overhead on Summer Solstice at the latitude known as the Tropic of Cancer. Image Credit: NASA

The Sun is directly overhead at 23.5° North latitude (Tropic of Cancer) on the Summer Solstice. Image Credit: NASA

The Wet and Dry Seasons of South Florida

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Seasons are a way of dividing up the year based on changes in weather. The traditional four – winter, spring, summer and fall – are familiar to most people.  In the subtropical climate of south Florida, however, there are really only two – wet and dry. While traveling there recently, I had the chance to learn more about them.

The wet season typically runs from mid-May to November. It produces the vast majority of the region’s average annual rainfall, approximately 60 inches. Temperatures often reach into the 90s and humidity levels are high. With sea-breeze fronts developing along both the Atlantic and Gulf Coasts, thunderstorms can occur almost daily during the summer months.

The dry season runs from December to mid-May. Temperatures at that time of year range from the mid-50s to upper-70s and humidity levels are relatively low. On occasion, continental cold fronts dip down into south Florida, bringing near-freezing temperatures to the region. Any rain associated with these frontal systems tends to sweep through the area quickly. Only about 20% of the region’s average annual rain total falls during the winter months.

South Florida’s largest rainfall totals are usually associated with tropical storms and hurricanes, which are not uncommon between June and November.

Data Source: SERCC

Data Source: SERCC

Similar Weather for Easter and Christmas in NYC

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Easter and Christmas are major holidays associated with the beginning of two different seasons – spring and winter, respectively. Nonetheless, the weather conditions for their most recent occurrences in New York City were oddly similar.

The high temperature in Central Park yesterday, Easter Sunday, was 61°F and the low was 42°F.  Back on Christmas Day, December 25th, the high was 62°F and the low was 44°F, tying the record for the city’s third warmest Christmas. Conditions this Easter were only slightly above average for the date.

The warmest Easter on record for NYC, according to the local National Weather Service office, was in 1976 when the high temperature reached 96°F. The coldest was in 1940 when the high was only 31°F.

NYC Monthly Summary: March 2015

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March 2015 was a bit of a weather rollercoaster in New York City. We had highs ranging from a chilly 27°F to a relatively balmy 62°F. In the end though, with 23 out of 31 days posting below average readings, the cold won out. The extended cold snaps helped lower the city’s mean temperature for the month to 38.1°F, which is 4.4°F below normal. That makes March 2015 the coldest March the city has seen in 31 years.

In terms of precipitation, March 2015 was unusually snowy. In fact, according to the National Weather Service, it was NYC’s 6th snowiest March on record. The city measured 18.6 inches of snow in Central Park, which is a staggering 14.7 inches above average. We even had snow falling on the first day of spring.

Rainfall was also abundant. The city received 4.72 inches, which is 0.36 inches above average for the month.

Credit: The Weather Gamut.

Credit: The Weather Gamut.

Vernal Equinox 2015

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Today is the Vernal Equinox, the first day of spring in the northern hemisphere. The new season officially begins at 22:45 UTC, which is 6:45 pm Eastern Daylight Time.

The astronomical seasons are a product of the tilt of the Earth’s axis – a 23.5° angle – and the movement of the planet around the sun. Today, as spring begins, the Earth’s axis is tilted neither toward nor away from the sun.  This position distributes the sun’s energy equally between the northern and southern hemispheres.

Since the winter solstice in December, the arc of the sun’s daily passage across our sky has been moving northward and daylight hours have been increasing. Today, the sun appears directly overhead at the equator and we have approximately equal hours of day and night. The word “equinox” is derived from Latin and means “equal night”.

As a transitional season, spring is a time when the chill of winter fades away and the warmth of summer gradually returns. The largest increase in average daily temperature, however, usually lags the equinox by a few weeks.

Earth’s solstices and equinoxes. Image Credit: NASA

Earth’s solstices and equinoxes. Image Credit: NASA

The Earth’s axis is tilted neither toward nor away from the sun on the Vernal Equinox. Image Credit: NASA

The Earth’s axis is tilted neither toward nor away from the sun on the Vernal Equinox. Image Credit: NASA