An early heads up for Fall as there are sights galore in the sky.
If you are like me you sure could use a welcome break from the endless election coverage and the world in general. Fortunately Mother Nature has just what we need - the arrival of Fall in the Northern Hemisphere.
This year Fall officially arrives at 10:21 a.m. EDT on Thursday, September 22nd. Astronomically speaking this is the date and time of the Autumnal Equinox http://earthsky.org/astronomy-essentials/everything-you-need-to-know-september-equinox , the precise moment when the Sun is seen directly overhead at noon at the Earth’s equator.
Both the Northern and Southern Hemispheres will have almost equal amounts of daylight and night as the Sun rises due East and sets due West everywhere on the planet except for the poles. Seen from space http://earthobservatory.nasa.gov/IOTD/view.php?id=52248 the Earth is equally illuminated by the Sun. All of this is repeated during the Vernal Equinox which marks the arrival of Spring in the Northern Hemisphere around March 21st.
The Earth’s seasons - Fall, Winter, Spring and Summer - are caused by the Earth’s orbit around the Sun and the 23 1/2 degree tilt of our planet’s axis. This causes the amount of sunlight falling on the Earth’s Northern and Southern Hemispheres to constantly change. The two hemispheres are always opposite in their seasons - our Fall is their Spring while our Summer is their Winter.
If you are outside your residence at sunrise on Thursday take note of where the Sun rises - that is due East. Every morning at sunrise you will notice that the Sun is moving a little bit to the right, or towards the South at sunrise. This will continue until the Sun reaches a point on the horizon that marks its farthest point South - which marks the first day of Winter and the shortest amount of daylight for the year - the Winter Solstice. The Sun will start to move to the left or North on the horizon and the amount of sunlight will increase until around June 21st, the Summer Solstice, the greatest amount of daylight for the year. Then the season cycle begins anew with the Sun heading South on the horizon.
The arrival of Fall means that the Sun is getting lower in the sky each day at noon and the nights are growing longer and cooler. Our trees will soon begin to take on the beautiful colors of Fall and the air will have that smell that only can happen this time of year.
The longer nights allow us to better enjoy the night sky. After sunset beautiful and bright Venus awaits our gaze low in the western sky. Venus will be getting higher in the sky in the coming months and will be a stunning sight.
Mars and Saturn are still visible in the southwestern sky after dark - Mars is the brighter of the two - as is the summer Milky Way. You will need a dark sky site such as Shenandoah National Park https://www.nps.gov/shen/index.htm to see the glorious Milky Way. You can get updates on the Fall colors using the Park’s website and I hope you can make it to one of my “Let’s Talk About Space at Shenandoah National Park” presentations http://www.goshenandoah.com/activities-events/astronomy .
High in the East you can see the Great Square of Pegasus and above the Eastern horizon at 11 p.m. stands the beautiful Seven Sisters or Pleiades star cluster. That bright star in the northeast is Capella and the lonely stellar sentinel in the south is Fomalhaut.
The elusive planet Mercury will be visible above the eastern horizon about a half hour before sunrise for the next two weeks. On September 29th use the very slim crescent Moon as a guide to find Mercury as the two will be very close together - binoculars will help.
Also visible in the East from a dark sky site about two hours before sunrise is the ghostly Zodiacal Light (ZL) http://earthsky.org/astronomy-essentials/everything-you-need-to-know-zodiacal-light-or-false-dawn . I have seen it from Shenandoah National Park as you can see in my pic. The ZL rises through Venus towards the Milky Way which crosses diagonally.
Enjoy the clean, crisp air of Fall and the lengthening nights. Breathe deep while you gaze skyward to see the stars - you’ll be glad you did.
Sky Guy in VA
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