BETHLEHEM, Pa. — Brad Klein reviews the week’s astronomical highlights with Bethlehem’s ‘Backyard Astronomy Guy,’ Marty McGuire.
This Sunday, September 22, is the start of ‘astronomical autumn’ as the Earth reaches equinox in its journey around the sun.
The seasons on Earth are a result of the planet’s tilted axis, combined with its orbit. And Sunday morning, our planet passes through the point in space, “when the sun is vertical at the equator. Meaning the Earth's axis is perpendicular to the sun's rays,” according to McGuire.
In the Lehigh Valley we think of this as the ‘Autumnal Equinox’ and the start of autumn. While in the southern hemisphere, the same moment marks the ‘Vernal Equinox’, and the start of spring.