September 2025 Skywatch

Authored By: ʻImiloa Astronomy Center

Featured Maunakea Observatory Discovery

Astronomers using the Smithsonian Submillimeter Array (SMA) on Maunakea have helped determine the three-dimensional structure of one of the night sky’s most iconic objects - the Ring Nebula. The research team determined the nebula to have an ellipsoidal shape using SMA radio-wavelength mapping of emission from carbon monoxide (CO) gas. The CO emission reveals cold, molecular gas that envelopes the hot gas and dust seen in images of the nebula obtained by the Hubble Space Telescope (HST) and, more recently, the James Webb Space Telescope (JWST).

"We looked at the data and the ellipsoidal structure was obvious, so we could put together a simple geometrical model. Now, we understand the structure of this nebula," said project lead Professor Joel Kastner of the Rochester Institute of Technology. "The James Webb Space Telescope gives us a collapsed image of what the object looks like in the sky. The SMA allows us to accurately measure the velocities of the molecular gas in the nebula, so we can see what's moving toward or away from us."

Astronomers have theorized that the nebula is ring-shaped or has a soap bubble structure, but the model created from the SMA data revealed it is an ellipsoid. The SMA data pinpoint the velocities and locations of the carbon dioxide molecules ejected by the dying star that generated the Ring Nebula and reveal its 3D shape, which can't be inferred from telescopic images, even using powerful NASA space observatories like HST and JWST. 

The modeling allowed the astronomers to estimate that roughly 6,000 years have elapsed since the dying star, then a red giant, ejected the molecular gas that envelopes the nebula. The SMA data also reveal telltale signatures of the influence of a companion star to the former red giant at the center of the nebula, in the form of high-velocity blobs of gas that appear to have popped out of each end of the ellipsoidal shell.

More information can be found at the following press release:

https://www.rit.edu/news/rit-professor-leads-research-showing-true-structure-iconic-ring-nebula

Special Events

Saturn at Opposition - September 21

Saturn will be at its closest approach to Earth and will be fully illuminated by the Sun. It will be brightest now compared to the rest of the year and will be visible all night long. This is the best time to view the planet. A medium-sized or larger telescope will enable you to see Saturn’s rings and brightest moons.

September Equinox - September 22

This is the first day of fall in the northern hemisphere. At this time, the Sun will shine directly on the equator and there will be nearly equal amounts of day and night throughout the world.

Neptune at Opposition - September 23

Neptune will be at its closest approach to Earth and will be fully illuminated by the Sun. This is the best time to view the planet. However, Neptune’s extreme distance from Earth means that it will only be visible in the most powerful of telescopes.

Evening Observing

At 8:00pm, Mānaiakalani will be the dominant starline in our night sky with Kamakaunuiamāui pulling the Milky Way across our southern sky. Kaʻiwikuamoʻo will now be setting in the western horizon. With Kaʻiwikuamoʻo setting we now can see the KalupeaKawelo when we look toward the direction of hikina (east)

Morning Observing

At 5:00am just before the sun rises, the star line Kekāomakaliʻi will be at its zenith slowly beginning to creep into position to inform us of our winter season. Within this star line is the brightest star in the night sky called Aʻā (Sirius), as well as the constellations of Kaheiheionākeiki (Orion) and Makaliʻi (Pleiades).