Given the right weather conditions, you will be able to see the harvest moon tonight. And if you have a mind to, and feel sufficiently inspired, you can also echo Thomas Hardy's words, and say:
Thy shadow, Earth, from Pole to Central Sea
Now steals along the Moon's meek shine
In even monochrome and curving line
Of imperturbable serenity.
Because tonight the harvest moon will be eclipsed.
Traditionally, the harvest moon is the full moon nearest to the autumn equinox on September 21st, and its reputation lies in its very bright appearance.
Moonrise throughout the lunar cycle occurs a little later each day by an amount of time known as the retardation. The mean value of the retardation is about 50 minutes - but it varies.
It is at its maximum of well over an hour around the time of the vernal equinox, and at a minimum in the autumn so that at this time of the year, to the casual observer, the moon appears to rise at the same time, around sunset, for several successive nights, and almost seems to replace the sun as it illuminates the evening sky.
An eclipse occurs on those relatively rare occasions when the sun, the moon and the Earth find themselves in an exact straight line. In the case of a lunar eclipse the sun is, as it were, behind the Earth, and the full moon passes for a time through the Earth's shadow. The diameter of this shadow is about 5,000 miles, more than double that of the moon itself, so the moon may take well over an hour to pass through it.
Lunar eclipses can be seen anywhere in the world where the moon happens to be above the horizon at the appropriate time, but this brings us to a factor which will, as it were, take the shine from the event this evening.
The moon will meet the outer fringes of the Earth's shadow shortly after 5 p.m., and total eclipse will last for about an hour from 7.15 p.m. Since, however, the moonrise in Ireland will not occur until nearly 7.30 p.m., we will miss the beginning of the spectacle, and may have to be content with a good view of only its final stages.
If the Earth had no atmosphere, the eclipsed portion of the moon would be jet black and totally invisible. Usually, however, our atmosphere tends to bend the passing rays of light into the shadow, so that the dark portion typically displays a copper-coloured tinge. How coppery or black the harvest moon will be on this occasion we must wait to see.