Wandering through the realms of the cosmos, pondering its huge vastness

Posts tagged “vernal equinox

March Equinox 2012

It’s equinox time again, and this year’s March equinox took place today at precisely 5:14 a.m. GMT, or Universal Time (13:14 in Manila). The March equinox was also known as the “spring equinox” in the northern hemisphere and “autumnal (fall) equinox” in the southern hemisphere as this event  marks the change of seasons — the beginning of spring in the northern part of the globe and autumn in the south.

During equinox, night and day are nearly exactly the same length – 12 hours – all over the world. This is the reason it’s called an “equinox”, derived from Latin, meaning “equal night”.

However, even if this is widely accepted, it isn’t entirely true. In reality equinoxes don’t have exactly 12 hours of daylight. A good website for looking at sunrise and sunset times in Manila can be found here. The best one for checking the bearing (direction) of sunrise or sunset anywhere in the world is the US Naval Observatory.

A more appropriate way to define equinox is given by astronomers. According to its astronomical definition, an equinox is the moment when the sun arrives at one of two intersection points of the ecliptic, the sun’s path across the sky, and the celestial equator, earth’s equator projected onto the sky.

Image credit: Chris de Villiers (www.skywatch.co.za)

My plans today were to head on the top of a high place and catch the sun setting due west. Sadly, the weather was not very good and the visibility was terrible.

Had I been able to see the sun it would have set due west.

Everyone always says that the sun rises in the east and sets in the west, but if we were really aware of our surroundings and more attuned to the sky we would realize that this is not true. In fact this is only true for two days out of the entire year and those are during equinoxes.

By studying the sun’s position in the sky over the course of a year from the same location, one can notice that its rising and setting positions are changing by more at a particular time of year than at any other time.

The amount of change in the location of the rising and setting of the sun  throughout the year depends upon where your viewpoint is. However, irrespective of where you are on the globe, the Sun will always rise exactly east and set exactly west during equinoxes (on March 20/21 and September 20/21)

On the other hand, near the solstices the sunrise position slows its change to close to a ‘standstill’  (the name ‘solstice’ being derived from the Latin for ‘sun standing still’).

Path of the Sun in the sky at different times of the year. Image copyright: Addison-Wesley

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Seasons Without Borders: Equinox March 2012

swb_equinox_march2012

Wherever you are on 20 March, 2012, celebrate your season in the cycle of life with Astronomers Without Borders.  Enjoy your own unique Equinox this year—and why not tell others about the experience?  Being mindfully aware of your place on this moving Earth may bring out the storyteller and poet in you.  AWB invites you to share your event reports and poems at the AWB Members’ Blog and AWB Astropoetry Blog. Send your poems to: astropoetry@astronomerswithoutborders.org.

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Happy March Equinox!

Before I forgot… Happy Equinox, everyone! 🙂

The word “equinox” derives from the Latin words meaning “equal night” and refers to the time when the sun crosses the equator. At such times, day and night are of nearly equal length everywhere in the world.

While the March equinox marks the beginning of spring in the northern hemisphere, it is the start of autumn in many parts of the southern hemisphere.

 

an illustration of the March Equinox, not to scale

During the equinox, the length of night and day across the world is nearly, but not entirely, equal. This is because the day is slightly longer in places that are further away from the equator, and because the sun takes longer to rise and set in these locations. Furthermore, the sun takes longer to rise and set farther from the equator because it does not set straight down – it moves in a horizontal direction.

Moreover, there is an atmospheric refraction that causes the sun’s disk to appear higher in the sky than it would if earth had no atmosphere.

How high the Sun gets in your sky, and how long it is above the horizon during the day, depend not only on the season, but also on your latitude.

 

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