This week two of the brightest planets join forces, and sky-watchers celebrate the change of seasons with a bright full moon.
Saturn and Venus. Starting on Monday, September 16 after sunset, Venus and Saturn will be having a close encounter that will last most of the week. Low in the southwest sky, the second planet from the Sun will be the first visible—as the brightest star-like object in the entire heavens.
Look carefully next to Venus—binoculars may help—and fainter Saturn will pop out of the glare of dusk. Remember that since the two worlds are hot on the heels of the setting sun, they sink below the horizon less than an hour later.
The lord of the rings will pass only 4 degrees above the goddess of love—less than the width of your three middle fingers at arm’s length. As the week progresses both planets will appear lower in the sky each night with Venus sliding a bit towards the left of Saturn.
Even the smallest backyard telescope will show off Saturn’s iconic rings and even some of its brightest moons—like Titan and Enceladus.
Full Harvest Moon. Watch the near full moon rise soon after sunset, Wednesday, September 18, and reach official full moon status at 7:13 am EDT the next morning around when sun rises.
The full moon nearest the fall equinox is known as Harvest Moon and was probably coined by farmers in the Northern Hemisphere since its added light is said to have helped them gather in their crops.
Binoculars will easily show off the moon’s dark patches visible with the naked eyes. Called plains or maria in Latin, meaning seas, these are vast, ancient lava plains formed over billions of years ago when magma from the moon’s interior spilled out onto the surface, triggered by giant asteroid impacts.
With telescopes, the views get even more exciting—you can get sharp views of hundreds of ridges, mountains, cliffs, and craters up close.
Check out the Hitchhiker’s Guide to the Moon—a very detailed website dedicated to showing you exactly what you can see on the surface of the moon—generated for every day of the calendar.
Moon and Uranus. All night long on Thursday, September 19 the seventh planet from the Sun, Uranus, will park itself near the moon.
The green giant is only 4 degrees away from the moon. The cosmic odd-couple will appear about four degrees apart in the sky—equal to 8 full moons side-by-side.
The green-colored ice giant has four times the width of Earth, but since it lies nearly 1.9 billion miles (3.1 billion kilometers) away from Earth, it’s barely visible to the naked eye—and only in very dark, pristine skies.
With the glare from the nearby moon, binoculars will be your best bet in spotting Uranus. Just look for a tiny greenish-blue disk in the field of view. By the way, the absorption of red light by methane in the atmosphere is what gives Uranus it’s cool cyan coloring.
Equal Day and Night. Autumn equinox is at 4:44 pm ET on Sunday, September 22, and officially marks the time of year we kick off the fall season in the northern hemisphere and the start of spring in the southern hemisphere. The word equinox comes from Latin meaning “equal night” and refers to the 12 hour long day and night that occurs only twice a year.
Looking at the mid-day position of the sun over the summer season, Northern Hemisphere sky-watchers will notice that it has been slowly sinking closer to the southern horizon, and creating ever longer shadows.
It’s only on the spring and autumnal equinox that the Sun rises due east and sets due west.
Astronomically speaking, the September equinox marks one of the four major turning points in the cycle of seasons. The Earth spins on its axis, which is tilted at 23.5 degrees with respect to its orbital plane. On these days, however, the Earth’s axis is neither tilted away nor towards the Sun, but has both northern and southern hemispheres experiencing equal amounts of sunshine.