September Equinox Marks the Start of Fall 2022

Complemented by cooler temperatures and falling leaves, the September equinox marks the beginning of the fall season for the Northern Hemisphere. This year’s autumnal equinox (for the Northern Hemisphere) or spring equinox (for the Southern Hemisphere) occurs on Sept. 22 at 8:04 p.m. CDT.

An illustration of the March (spring) and September (fall or autumn) equinoxes.
An illustration of the March (spring) and September (fall or autumn) equinoxes. During the equinoxes, both hemispheres receive nearly equal amounts of daylight. (Image not to scale) Credits: NASA/GSFC/Genna Duberstein

During an equinox the Sun shines directly over the equator resulting in nearly equal amounts of day and night throughout the world – except for the North and South Pole where the Sun approximately straddles the horizon for the entire day, according to Alphonse Sterling, an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama. Following the autumnal equinox, the Sun gradually continues to rise later and set earlier in the Northern Hemisphere – making the days shorter and the nightfall longer. The opposite is true in the Southern Hemisphere where the days begin to last longer.

Seasons are caused by Earth’s tilted axis which always points in the same direction. As Earth orbits around the Sun, the angle of sunlight that the Northern and Southern Hemispheres receive is different. “On the June solstice (summer) in the Northern Hemisphere, sunlight is more direct, so it warms the ground more efficiently,” said Mitzi Adams an Assistant Manager in the Heliophysics and Planetary Science Branch at Marshall. “In the Southern Hemisphere, sunlight is less direct (winter), which means that the ground is not heated as easily.”

A visual aid to better understand how the Earth's tilted axis causes the different seasons throughout the year in the Northern and Southern Hemispheres.
A visual aid to better understand how the Earth’s tilted axis causes the different seasons throughout the year in the Northern and Southern Hemispheres. Credit: NASA/Space Place

Astronomical seasons are defined by the Earth’s journey around the Sun, while meteorological seasons are guided by annual temperature cycles. Meteorologists group the seasons into time periods that line up with the weather and monthly calendar:  December through February is winter, March through May is spring, June through August is summer, and September through November is fall. Astronomical seasons are marked by the equinoxes and solstices that each happen twice a year. Solstices are when the Sun appears to reach the lowest or highest point in the sky all year; they mark the beginning of summer or winter. Solstices are commonly referred to as the longest (summer solstice) or shortest (winter solstice) day of the year.

The September equinox is a time that welcomes Earthlings to a new season. To those in the Northern Hemisphere, enjoy the beginning of milder weather and say hello to early sunsets and late sunrises.

by Lane Figueroa

Jupiter to Reach Opposition, Closest Approach to Earth in 59 Years!

Stargazers can expect excellent views of Jupiter the entire night of Monday, Sept. 26 when the giant planet reaches opposition. From the viewpoint of Earth’s surface, opposition happens when an astronomical object rises in the east as the Sun sets in the west, placing the object and the Sun on opposite sides of Earth.

Jupiter’s opposition occurs every 13 months, making the planet appear larger and brighter than any other time of the year. But that’s not all. Jupiter will also make its closest approach to Earth since 1963 – almost six decades ago! This happens because Earth and Jupiter do not orbit the Sun in perfect circles – meaning the planets will pass each other at different distances throughout the year. Jupiter’s closest approach to Earth rarely coincides with opposition, which means this year’s views will be extraordinary. At its closest approach, Jupiter will be approximately 367 million miles in distance from Earth, about the same distance it was in 1963. The massive planet is approximately 600 million miles away from Earth at its farthest point.

Photo of Jupiter with Red Spot
This photo of Jupiter, taken from the Hubble Space Telescope on June 27, 2019, features the Great Red Spot, a storm the size of Earth that has been raging for hundreds of years. Credits: NASA, ESA, A. Simon (Goddard Space Flight Center), and M.H. Wong (University of California, Berkeley)

“With good binoculars, the banding (at least the central band) and three or four of the Galilean satellites (moons) should be visible,” said Adam Kobelski, a research astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “It’s important to remember that Galileo observed these moons with 17th century optics. One of the key needs will be a stable mount for whatever system you use.”

Kobelski recommends a larger telescope to see Jupiter’s Great Red Spot and bands in more detail; a 4 inch-or-larger telescope and some filters in the green to blue range would enhance the visibility of these features.

According to Kobelski, an ideal viewing location will be at a high elevation in a dark and dry area.

“The views should be great for a few days before and after Sept. 26,” Kobelski said. “So, take advantage of good weather on either side of this date to take in the sight. Outside of the Moon, it should be one of the (if not the) brightest objects in the night sky.”

As the Moon rose over the Wasatch Mountains near Salt Lake City on Feb. 27, 2019, the planet Jupiter could be seen, along with three of its largest moons.
As the Moon rose over the Wasatch Mountains near Salt Lake City on Feb. 27, 2019, the planet Jupiter could be seen, along with three of its largest moons. Stargazers should have a similar view during Jupiter in Opposition on Monday, Sept. 26. Credits: NASA/Bill Dunford

Jupiter has 53 named moons, but scientists believe that 79 moons have been detected in total. The four largest moons, Io, Europa, Ganymede, and Callisto, are called the Galilean satellites. They are named after the man who first observed them in 1610, Galileo Galilei. In binoculars or a telescope, the Galilean satellites should appear as bright dots on either side of Jupiter during opposition.

NASA’s Juno spacecraft, which has been orbiting Jupiter for six years, is dedicated to exploring the planet and its moons. Juno began its journey in 2011 and reached Jupiter five years later. Since 2016, the spacecraft has provided incredible images and data about Jupiter’s lively atmosphere, interior structures, internal magnetic field, and magnetosphere.

Scientists believe studying Jupiter can lead to breakthrough discoveries about the formation of the solar system. Juno’s mission was recently extended until 2025 or until the end of the spacecraft’s life. Learn more about Juno.

The next major project for Jupiter exploration is the Europa Clipper. This spacecraft will explore Jupiter’s iconic moon, Europa, which is known for its icy shell and vast ocean that lies beneath its surface. NASA scientists aim to find whether Europa has conditions able to sustain life.  Europa Clipper’s targeted launch is currently scheduled for no earlier than October 2024.

Learn more about the giant planet. And if you want to know what else is happening in the sky for September, check out  Jet Propulsion Laboratory’s latest “What’s Up” video:

by Lane Figueroa