365daysDate: September 20, 2009

Title: September Equinox: International Unity Day


Podcaster: Judith Young

Organization: The Foundation for Astronomy and Spirituality, Inc.:
University of Massachusetts at Amherst:

Description: What are the astronomical characteristics of the September Equinox? This podcast covers the uniqueness of the Equinox in terms of the sunrise and sunset directions, the length of time the Sun is above the horizon and below, and the location on Earth where the noon-time Sun is seen to be directly overhead. Also included are the differences seen in the sky for observers at the North and South poles, and at mid-northern and mid-southern latitudes. Given the commonality of experience for observers all across the globe on the Equinox, in terms of day/night length and sunrise/sunset direction, it is suggested that we celebrate the Equinox as ‘International Unity Day.’

Bio: Judith Young, Ph.D., is a tenured full professor of astronomy at the University of Massachusetts, where she has taught for 25 years. She has authored over 120 scientific publications, and her work on star formation in galaxies is internationally acclaimed. She has received awards from the American Astronomical Society and American Physical Society for her research, and she has received awards for her teaching and outreach at U.Mass. She has a not-so-secret-love: inspired by a Sunwheel on Blackfeet Indian territory in Montana, Dr. Young built the first original stone circle calendar on a University campus in the world. She’s given over 300 talks to over 9,000 visitors at the Sunwheel since 1997, where she hosts solstice and equinox sunrise and sunset gatherings every 3 months. She loves teaching people about the sky to help them feel at home in the Universe, and she dreams of inspiring the building of stone circle calendars the world over.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Wilfred Nijman, a 54-year old astronomy student who would like to remind you that it is never too late to start your studies by distance learning at


“September Equinox – International Unity Day”
Podcast – September 20, 2009
365 Days of Astronomy

Hello everyone — my name is Dr. Judith Young, named Joyous Judy by my daughter, and I’m an astrophysicist and professor of astronomy and the University of Massachusetts at Amherst where I have taught for 25 years. I love teaching, and I especially love getting people outside to pay attention to the sky. To assist in this, I have built a massive astronomically aligned stone circle – a Sunwheel – on the U.Mass. Amherst campus, with fourteen 8’-10’ tall stones in a circle 130’ across, marking the 4 cardinal directions and the rising and setting directions to the Sun on the solstices and equinoxes. I invite the public to attend sunrise and sunset gatherings at the Sunwheel at the beginning of each season, with the goal of bringing greater awareness and understanding of the seasons and of the solstices and equinoxes to everyone. Since 1997, I have taught what I call “Everyday Astronomy” to some 10,000 visitors standing amidst the stone circle, and over 25,000 individuals have explored the Sunwheel on their own.

In a few days, on September 22nd, all of us on Earth will experience the September Equinox – the beginning of autumn in the Northern hemisphere and the beginning of spring in the Southern hemisphere. At 21:19 Universal Time on the 22nd, or 5:19 p.m. Eastern Daylight Time, the instant of Equinox will occur. Astronomically, at that instant, the Sun will be located in the sky exactly on the celestial equator, that is, precisely centered on the imaginary extension of Earth’s equator into space.

What is the Equinox? Well, there are several special characteristics of that day for everyone on the Earth. First, the Sun rises due East and sets due West, and only on the Equinox is that true. Every other day of the year, the Sun rises either South of due East or North of due East, and sets either South of due West or North of due West. You thought that the Sun rises in the East every day? Not due East every day – just on the Equinox. And you thought the Sun sets in the West every day? Not due West every day – just on the Equinox. And on the Equinox, this due East rising and due West setting is best seen if you have no hills, trees, or buildings on the horizon.

Second, on the Equinox the Sun is up for 12 hours and down for 12 hours. This is the basis for the term equinox in the first place, from the Latin and meaning “equal night” – however, the situation is most accurately described as equal Sun up and equal Sun down. Strictly speaking, this 12 hours of Sun up and 12 hours of Sun down is seen when there are no hills on the horizon.

So here we have 4 characteristics of the Equinox –
1. the Sun rising due East,
2. the Sun setting due West,
3. the Sun up for 12 hours, and
4. the Sun down for 12 hours.

And the amazing thing is that everyone on Earth sees this on the Equinox. (Keep in mind that I am excluding for now the special cases of what the Equinox looks like to the penguins and polar bears at the North and South Poles.) So you may be located in Australia, or Ireland, or Ecuador, or Amherst, Massachusetts (where I am,) and whether you are in the Southern hemisphere or the Northern hemisphere or at the equator, on the Equinox you will see the Sun rise due East and set due West, with 12 hours of Sun up and 12 hours of Sun down.

Just think about it – on the day of the Equinox, all creatures inhabiting the Earth will experience the same thing with regard to the direction of sunrise and sunset, and with regard to the length of time the Sun is up and the length of time the Sun is down. On the basis of this commonality of experience, a visitor to the Sunwheel on the Equinox many years ago suggested that we call the Equinox “International Unity Day”, and I fell in love with that idea. So, let us celebrate this Equinox and every Equinox as “International Unity Day”. And I do not mean celebrating just at the instant of the Equinox, or just for an hour at noon on the Equinox, but for the whole day. Imagine all of us experiencing international unity for a whole day, extending peace and kindness to others for a whole day the world over. Among all the inhabitants of Earth. This is what we as human beings could choose.

And although there is a great deal of similarity worldwide to our experience of the Sun on the Equinox, astronomically speaking the major difference seen from place to place is how high the Sun gets in the sky at noon. For example, in Quito, Ecuador (located on Earth’s equator) on the Equinox the Sun will be directly overhead at local noon and you will cast no shadow. In fact, anyone anywhere on Earth’s equator on the Equinox will have the Sun directly overhead at local noon and will cast no shadow. Here in Amherst, at latitude 42° North, the noontime Equinox Sun has an altitude of 48° above the southern horizon. In Cusco, Peru, at latitude 13° South, the noontime Equinox Sun there has an altitude of 77° above the northern horizon. And still, in each location the Sun rises due East and sets due West, and spends 12 hours up and 12 hours down.

Viewing our planet from outer space, what is unique in relation to every other day of the year is that all latitudes of planet Earth are illuminated by the Sun on the Equinox. That is, our planet is bathed in light from the North Pole to the South Pole. This is only true on the Equinoxes, with the Sun over the equator, so both the North and South Poles get some degree of light along with every latitude in between. Then as Earth rotates, each location is illuminated by the Sun half of the time (a 12 hour day), and spends the other half of the time turned away from the Sun (a 12 hour night). Except at the Poles.

A special case arises on the Equinox for observers at the North and South Poles. There, at the northern and southern endpoints of the Earth’s imaginary axis of rotation, the Sun is seen to circle around the horizon on the day of the September Equinox, slowly (in about 24 hours) spiraling out of view as seen from the North Pole, and slowly (in about 24 hours) spiraling into view as seen from the South Pole. The September Equinox, then, marks the beginning of 6 months of without Sun at the North Pole, and the beginning of 6 months of light at the South Pole.

Finally, the September Equinox in the Northern hemisphere marks the beginning of autumn, when days become shorter than nights and the Sun at noon will be getting lower in the sky. And the September Equinox in the Southern hemisphere marks the beginning of spring, when days become longer than the nights and the Sun at noon will be getting higher in the sky. For observers in both hemispheres, September 22nd marks the beginning of the 6-month period of time when the Sun is seen rising South of East and setting South of West, which will persist until another Equinox passes next March.

On the September Equinox, I invite you to join me in witnessing the passing of the seasons by watching the Sun rise and set. If you live in Massachusetts, please join me among the tall standing stones in the U.Mass. Sunwheel on September 22nd and 23rd. If you live far away, you can create your own astronomically aligned stone circle – for information on programs I lead and on how to build a Sunwheel, visit and

And finally, I invite you to celebrate this Equinox and every Equinox as “Interntational Unity Day”. Let us individually and collectively create the experience of international unity, offering peace and understanding and kindness to All of Life for a whole day the world over. Inspired by the Sun, this is what we as human beings could choose. What are we waiting for?

End of podcast:

365 Days of Astronomy
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