Tonight – October 25, 2016 – the waning crescent moon crosses the Earth’s orbital plane going from south to north. So, as the world wakes up before daybreak tomorrow (October 26), the moon will on or near the ecliptic – Earth’s orbital plane projected outward onto the great dome of sky. When the moon crosses the ecliptic, going from south to north, the moon is said to be at its ascending node.
More about ascending node below, and about what it means for solar and lunar eclipses viewed from our world. But first, look at the chart above. The moon is about to sweep past the very bright planet Jupiter in the east before dawn. On the morning of October 26 note that the bow of the lunar crescent points in Jupiter’s direction.
The moon will be edging closer to Jupiter in the next few mornings, as shown on the chart below:
Okay so … what’s so special about the moon at ascending node? It’s only when the moon is on the ecliptic – at ascending or descending node – that an eclipse can occur. For us in North American, the very special date of a very special eclipse will be August 21, 2017. That’ll be the first total solar eclipse visible from the contiguous United States since 1979. No kidding … make your hotel reservations now!
The moon reaches its ascending node on October 26, 2016 at 0144 UTC. At U.S. time zones, that means the moon crosses the ecliptic – Earth’s orbital plane – on October 25 at 9:44 p.m. EDT, 8:44 p.m. CDT, 7:44 p.m. MDT and 6:44 p.m. PDT.
At that moment, the waning crescent moon will still be below the U.S. horizon, because the moon at this phase appears in the morning sky. Many of our friends in the world’s Eastern Hemisphere will actually see the moon at the moment that it crosses the ecliptic.
The moon’s orbital plane around Earth is inclined by about 5o to the Earth’s orbital plane around the sun. Twice (sometimes three times) in one calendar month, the moon crosses the Earth’s orbital plane at points called nodes. Once again, when the moon intersects the ecliptic (Earth’s orbital plane) going from south to north, it’s called an ascending node; and when the moon crosses the ecliptic from north to south, it’s called the descending node.
There are at least two solar eclipses and two lunar eclipses every calendar year. Yet, it’s possible for both lunar eclipses to be rather hard-to-see penumbral lunar eclipses, as is the case in 2016.
The period of time between the moon’s successive returns to its ascending (or descending) node is referred to as the nodal or draconic month, a mean period of 27.21 days. In contrast, the time period between successive new moons (or successive full moons) is called the lunar or synodic month, a mean period of 29.53 days. The mean nodal month is some 2.3 days shorter than the mean lunar month.
Two nodal months ago – on September 1, 2016 – the close alignment of the new moon with its ascending node gave Africa an annular eclipse of the sun on September 1, 2016.
Oftentimes, in the following year, the new moon will closely realign with its ascending node some 11 days earlier than in the previous year. Sure enough, that’s the case for the long-awaited American solar eclipse in 2017. The new moon will realign with its ascending node to stage the total solar eclipse on August 21, 2017.
Bottom line: No eclipse will happen in October, 2016, because it’ll be a waning crescent moon – not the new moon or full moon – that aligns with the moon’s ascending node.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.