Is it possible for the path of totality to run along the equator, not just cross it?
Maybe on an equinox?
I think that for that to happen, the Moon’s orbit would have to be within the plane of the equator, which it isn’t.
Thats what I was thinking. But does the earths axis wobble enough that at some distant time in the future it would be enough?
Can’t happen because the moon does not orbit on the plane of the equator. Remember the moon orbits on an inclination and the earth itself is tilted. In short, from earth, the moon looks like it moves up and down in its orbit.
I don’t think the moon would necessarily have to orbit in the plane of the equator for there to be a solar eclipse that roughly followed the equator. You would need the Sun, Moon, Earth, and vernal point (or autumnal point) to all be in a straight line. Since the lunar nodes precess around the ecliptic every 18.6 years, it’s conceivable that this could happen; basically, you’d need the moon to be new at the same time that the lunar nodes precess past the vernal/autumnal equinox.
The only deviation from the equator would then be due to the motion of the moon as it crosses the ecliptic. That said, it’s not clear to me how much of a deviation (eclipse-latitude-wise) this would cause; it might well be substantial.
I’m pretty sure (without checking) that the path of the eclipse is almost entirely do to the rotation of the earth just like the apparent movement of the sun and the moon are almost entirely due to the Earth’s rotation and not, for example, the moon’s orbit around the Earth. On the day of either equinox, the sun is essentially directly above the equator all day (and approximately so for a few days before and after) So if the moon’s orbit happened to be crossing the equator at the time, it would essentially stay directly between the sun and the earth directly above the equator as the earth rotated below it and the path of totality would include the equator (as well as a bit north and south of it).
This is not to say that a total eclipse on the equinox would have to have a path of totality along the equator because the moon might be “off center” a bit.
It’s also possible there is some resonance in the orbits so that total eclipses can never occur on equinox days. I don’t know about that.
The shadow itself would move at just slightly faster than the speed of the Moon, since the Earth-Moon distance is small compared to the distance to the Sun. And the Moon takes a little under 30 days to make a complete cycle, compared with a single day for the Earth’s surface, but the Moon’s orbital radius is about 80 times the radius of the Earth. So the actual speed of the Moon (and hence, of the Moon’s shadow) is nearly three times the speed of the surface of the Earth, and so an eclipse path would be dominated by the Moon’s motion.
Wouldn’t it have to though to trace its shadow on the earth’s equator?
Unless you are saying (just thinking out loud here…I certainly do not know the math) that while the moon seems to move up and down in its orbit (from our perspective) for a few hours that movement is not significant enough to make a difference. It would, roughly, track along the equator for a few hours. “Roughly” as in not perfectly (that is not possible) but close enough to keep the equator in totality for the duration. At least in theory even if it is a super rare occurrence.
If you look at an eclipse map, you’ll note that the typical eclipse does indeed wander in latitude during its eight or twelve hours of duration, sometimes changing course in mid-day.
The wandering is driven by two factors: the rotation of the earth and the changing declination of the moon as it orbits the earth. (The sun also changes in declination, but much more slowly.)
The rotation of the earth causes less “latitude wandering” to the extent that the rays of the sun fall perpendicular to the axis of rotation, as happens at the equinoxes. However, the movement of the moon causes more wandering to the extent that the moon is changing in declination, as happens most rapidly at the equinoxes and less so at the solstices.
These two effects somewhat offset. Look again at the map, blow it up to 150%, and you’ll notice relatively little correlation between the crookedness of an eclipse path and the time of year.
So to answer your question, no, it isn’t possible for the two effects to offset exactly and keep an eclipse path in a ruler-straight line all day. It can come somewhat close–some paths are straighter than others–but never be exact.
Thanks for all the responses. I had a feeling it wasn’t possible but couldn’t put my finger on why.
I have an offshoot question. A few of the mapped eclipses cross the equator on or about an equinox.
Has there ever been an instance where there was (or will be) a total eclipse crossing the equator, and crossed (will cross) it at the exact moment of equinox?
I would imagine programs like The Sky could grind this stuff out; sadly I do not possess that software.
Mar 9 2016 has one that is very close. You can see the curvature of most of the paths. There may have been one in the past that was closer to following the equator.
This tool is pretty interesting. It would be nice to see all the paths on a single map.
I was eyeing the Mar 20, 2034 eclipse. Crosses the equator but I don’t know what time the equinox occurs.