Sky Matters: The best times and places to see the lunar eclipse on September 7

And the Autumnal Equinox is on September 22 — this is the date when the length of day and night are equal for every one of Earth's 8.2 billion people

Mon, 01 Sep, 2025 - 06:05

Niall Smith

It’s September 7. You’re looking at an unobstructed eastern horizon at 8.04pm from your location somewhere in the south of the country. As you watch, you see the first edge of the full moon appear and within a few minutes almost half of it is visible.

A momentary glance to the western horizon reveals the setting sun, moving apparently in exact counterpoint to the moon. Our nearest celestial companion looks familiar; and yet somehow different. The golden glow that often accompanies the moon when it’s low to the horizon is replaced by a deeper red colour... some might say eerily red.

As you wait patiently for the moon to fully rise, you notice that the lower-left of the moon is not so red, and on closer inspection you realise you’re witnessing a partial lunar eclipse. It’s a relatively brief period lasting a total of no more than a few hours, when the earth passes between the sun and the moon, casting a shadow as it does so. A shadow that’s red in colour because our atmosphere preferentially transmits red light from the sun onwards in the direction of the moon — let’s not forget the sun is directly opposite the moon at this time.

For the September 7 lunar eclipse you may have to make the effort to get to a clear east-southeast horizon. Perhaps you’re already fortunate enough to live by an east-facing coast, or atop a mountain with a clear view all the way to an eastern horizon. If not, you’ll need to travel to such a place. Hardly a journey that will be recorded in the annals of human endeavour!

A previous lunar eclipse, seen from Ballyphehane, Cork. Picture: Neil Danton

By 8:07pm the partial eclipse is at its best, but by 8:56pm it is effectively over. If you live in other parts of Ireland the timings of moonrise will vary by a few minutes, but everything else remains the same.

A couple of weeks later, on September 22, the autumnal equinox arrives. This is the date when the length of day and night are equal — for every one of Earth’s 8.2 billion people. It has a psychological impact. Those of us living in the northern hemisphere are thinking about hunkering down as the nights get longer; those in the southern hemisphere are dreaming about longer, brighter and warmer days.

Perhaps surprisingly, the autumnal equinox and the partial lunar eclipse are related. In the early days of the solar system, about 4.8 billion years ago, the orderly motion of the planets we see today was about as far from that reality as one could imagine.

It was a time of immense building, destruction and rebuilding as countless collisions between objects in random orbits around the sun were the order of the day.

As earth struggled to get a foothold as a bone fide planet, it collided with another proto-planet the size of Mars and in that collision two things happened that are relevant to our story:

Firstly, the moon was born.

Secondly, the earth’s axis was tilted by 23.5°. That tilt gives us the monthly changes in the length of our day, our seasons with the annual cycles of life, and ultimately the autumnal (and spring) equinox.

A composite photo of the moon during a lunar eclipse. Picture: Clara Molden/PA Wire

If the moon didn’t exist, living on earth would be very different...

The stable 23.5° axial tilt would be replaced by chaotic changes from zero degrees (no seasons at all) to perhaps 85° (extreme seasons, each lasting thousands of years).
A day on Earth would last 6-8 hours, driving winds of higher velocity, making our current references to 'extreme weather events' look trivial.
Less mixing of deep ocean currents may have inhibited the establishment of early life (admittedly speculative).
And ancient civilisations who relied on lunar calendars would have evolved somehow differently.

Our lifeless, barren, nearest neighbour has been a much-overlooked friend of ours. If you do get to witness the partial eclipse, remember the moon is so much more than the Man in the Moon's 'pretty face'.