Vernal Equinox 2018

An early spring sunrise (2017)

Today at 12:15 PM EST, Winter officially ends and Spring begins in the Northern Hemisphere.  The day that this change occurs is known as the Vernal (Spring) Equinox.  The word equinox comes from the Latin words aequus (equal) and nox (night).  On the Equinox the sun strikes directly on the Equator resulting in approximately equal periods of day and night across the globe.

The Earth rotates around its axis approximately once every 24 hours.  However this axis is tilted at 23.5 degrees from the vertical.  The points on the globe that the axis revolves around are referred to as the North and South Poles.  The axis is always pointed toward the same location in the sky.  The North Pole points toward the "North Star" - Polaris.

At any given time, fifty percent of the earth is in sunlight (Day) and the other fifty percent is in darkness (Night).  However, because the Earth is tilted on its axis sunlight does not always strike the Earth at the same angle.  This means during different seasons different parts of the Earth will receive varying amounts of sunlight and darkness.
  
As the earth revolves around the sun, sometimes the North Pole is closer to the sun, sometimes the South Pole is closer to the sun.  When the North Pole is at its closest, the sun lights a larger portion of the Northern Hemisphere than it does the Southern Hemisphere.  When this happens, we experience Summer in Mid-Michigan and the Southern Hemisphere experiences Winter.  When the North Pole is at its furthest from the sun, we experience Winter and the Southern Hemisphere experiences Summer.  During our Northern Winter, the sun is striking a a larger portion of the Southern Hemisphere than it is the Northern Hemisphere.  On the Equinox, the poles are essentially perpendicular to the rays of the sun so locations in the northern and southern hemispheres should receive nearly equal hours of sunlight and darkness.

Spring flowers to get you in the mood for spring - Bloodroot (Sanguinaria canadensis)

Despite what most people think, the hours of daylight and night experiences on the Equinox are not perfectly equal.  Mt. Pleasant is located at 43 degrees 36 minutes north of the equator.  On the equinox, it experiences 12 hours 9 minutes worth of daylight.  A location located at 43 degrees 36 minutes south of the equator will receive approximately the same length of daylight. There is another lesser known event that occurred over the weekend - the Vernal Equilux.  Equilux means "equal light".  On Saturday March 17th, Mid-Michigan (and many other places in the Northern Hemisphere) received approximately 12 hours of daylight and 12 hours of darkness.

The hours of daylight that Mt. Pleasant receives each day will grow until it reaches 15 hours 24 minutes around the Summer Solstice.  Then our hours of sunlight will diminish until on the Winter Solstice we experience only 8 hours 57 minutes of daylight, before increasing again. 

Vernal Equinox 2017

The Skunk Cabbage knows that Spring has arrived.

Today at 6:28 AM EST, Winter officially ended and Spring began in the Northern Hemisphere.  The day that this change occurs is known as the Vernal (Spring) Equinox.  The word equinox comes from the Latin words aequus (equal) and nox (night).  On the Equinox the sun strikes directly on the Equator resulting in approximately equal periods of day and night across the globe.

The Earth rotates around its axis approximately once every 24 hours.  However this axis is tilted at 23.5 degrees from the vertical.  The points on the globe that the axis revolves around are referred to as the North and South Poles.  The axis is always pointed toward the same location in the sky.  The North Pole points toward the "North Star" - Polaris.

At any given time, fifty percent of the earth is in sunlight (Day) and the other fifty percent is in darkness (Night).  However, because the Earth is tilted on its axis sunlight does not always strike the Earth at the same angle.  This means during different seasons different parts of the Earth will receive varying amounts of sunlight and darkness.

 
As the earth revolves around the sun, sometimes the North Pole is closer to the sun, sometimes the South Pole is closer to the sun.  When the North Pole is at its closest, the sun lights a larger portion of the Northern Hemisphere than it does the Southern Hemisphere.  When this happens, we experience Summer in Mid-Michigan and the Southern Hemisphere experiences Winter.  When the North Pole is at its furthest from the sun, we experience Winter and the Southern Hemisphere experiences Summer.  During our Northern Winter, the sun is striking a a larger portion of the Southern Hemisphere than it is the Northern Hemisphere.

On the Equinox, the poles are essentially perpendicular to the rays of the sun so locations in the northern and southern hemispheres receive equal hours of sunlight and darkness.  Mt. Pleasant is located at 43 degrees 36 minutes north of the equator.  On the equinox, it experiences 12 hours 9 minutes worth of daylight.  A location located at 43 degrees 36 minutes south of the equator will receive approximately the same length of daylight.  The hours of daylight that Mt. Pleasant Experiences will grow until it reaches 15 hours 24 minutes around the Summer Solstice.  Then our hours of sunlight will diminish until on the Winter Solstice we experience only 8 hours 57 minutes of daylight, before increasing again.

Happy Autumn!

Fall at Mission Creek Woodland Park (Oct 2012)

Today is the Autumnal Equinox - or the day that the seasons change from Summer to Fall.  Officially the season changes for Mid-Michigan at 10:21AM (EDT). 

On this date, the hours of daylight and night are roughly equal.  The hours of daylight will decrease from now until the Winter Solstice on December 21st when there will only be 9 hours 2 minutes of daylight, before beginning to increase again to approximately 12 hours on the Spring Equinox and 15 hours 20 minutes on the Summer Solstice.

The weather this weekend is supposed to be beautiful, with highs near 70 degrees and nighttime lows near 50.  It should be a great time to go out and explore one of our many local parks and preserves.

Vernal Equinox 2016

Early Spring iris blooms in my garden (16 March 2016)

Yesterday at 12:30 AM (EST), Spring officially began for the Northern Hemisphere.  The date of the switch from Winter to Spring is known as the Vernal (Spring) Equinox.  On this date, the sun crosses over the celestial equator and begins to strike more directly on the Northern Hemisphere than the Southern Hemisphere.

If you were to rise each morning and observe the location of the sunrise from the exact same spot, you would find that the sunrise takes place in a slightly different location from one day to the next.  On the first day of Winter the sun would appear to rise far south of due east.

As winter progresses, the sun's position moves northward along the horizon a little bit each morning.  It will continue to move northward until the first day of Summer.  At that point each sunrise will move south along the horizon until the first day of Winter arrives again.  On the first day of Spring, the sun rises midway between these northern (Summer) and southern (Winter) maximums - the sun also rises at the midpoint on the first day of Fall (Autumnal Equinox).  Sunsets follow a similar pattern in the western sky. 

This shifting of the sunrise (and sunset) is due to the fact that the earth's axis is not directly perpendicular to the plane of its orbit.  If the earth's axis were perpendicular to the plane of its orbit, the sun would rise and set in the same location each day.  Instead the earth's axis is tilted approximately 23.5 degrees from the vertical - this is why globes are tilted.  For part of the year the Northern Hemisphere is tilted toward the sun (Spring and Summer) and for part of the year the Northern Hemisphere is tilted away from the sun (Fall and Winter).  Conversely, while the Northern Hemisphere is experiencing Summer the Southern Hemisphere is experiencing Winter; while the Northern Hemisphere is experiencing Winter the Southern Hemisphere is experiencing Summer.

Not only are the locations of the sunrise and sunset shifting, but the amount of daylight and darkness is also shifting.  On days when the position of the sun moves further north the amount of daylight grows slightly longer.  On days when the sunrise shifts southward the amount of daylight decreases slightly.

There are only two dates on which neither the Northern nor Southern Hemisphere is tilted more toward the sun.  On the equinoxes, both the poles line up with the direction of the earth's orbit and both hemispheres receive approximately equal amounts of daylight and darkness.

We are expecting snow later this week, but it officially Spring.  Get out there and enjoy it!

Autumn

A fall photo from 2008

Happy Autumn!  Last night at 10:29PM EST the seasons officially changed from Summer to Fall.  The date of this change is known as the Autumnal (Fall) Equinox.  The word Equinox means "equal night" and comes from the Latin words aequus (equal) and nox (night). On this date the sun is striking directly on the equator, resulting in approximately equal amounts of daylight and darkness around the globe.

To learn more about the Equinox please look at these posts about the Fall Equinox and the Spring Equinox.

Vernal Equinox

Today at 12:57 PM EST, Winter officially ends and Spring begins in the Northern Hemisphere.  The day that this change occurs is known as the Vernal (Spring) Equinox.  The word equinox comes from the Latin words aequus (equal) and nox (night).  On the Equinox the sun strikes directly on the Equator resulting in approximately equal periods of day and night across the globe.

The Earth rotates around its axis approximately once every 24 hours.  However this axis is tilted at 23.5 degrees from the vertical.  The points on the globe that the axis revolves around are referred to as the North and South Poles.  The axis is always pointed toward the same location in the sky.  The North Pole points toward the "North Star" - Polaris.


At any given time, fifty percent of the earth is in sunlight (Day) and the other fifty percent is in darkness (Night).  However, because the Earth is tilted on its axis sunlight does not always strike the Earth at the same angle.  This means during different seasons different parts of the Earth will receive varying amounts of sunlight and darkness.

As the earth revolves around the sun, sometimes the North Pole is closer to the sun, sometimes the South Pole is closer to the sun.  When the North Pole is at its closest, the sun lights a larger portion of the Northern Hemisphere than it does the Southern Hemisphere.  When this happens, we experience Summer in Mid-Michigan and the Southern Hemisphere experiences Winter.  When the North Pole is at its furthest from the sun, we experience Winter and the Southern Hemisphere experiences Summer.  During our Northern Winter, the sun is striking a a larger portion of the Southern Hemisphere than it is the Northern Hemisphere.

Today the North Pole and South Pole are both at the same distance from the sun.  Direct sunlight is falling directly on the Equator, lighting the Northern and Southern Hemispheres equally.  Here in Mid-Michigan (and the rest of the Northern Hemisphere), we are passing into Spring and the Southern Hemisphere is passing into Fall.

My attempt at a diagram showing how the sun lights different parts of the globe on different days

Fall

Happy Fall!

Yesterday at 4:44 PM EST, Summer ended and Fall officially began.  The first day of Fall is also known as the Autumnal (Fall) Equinox.  The word Equinox means "equal night" and comes from the Latin words aequus (equal) and nox (night).  On this date the sun is striking directly on the equator, resulting in approximately equal amounts of daylight and darkness around the globe.