The heatwave has been described as "critical" in the discovery of a henge, or circular enclosure in the Unesco World Heritage Site close to Newgrange in Co Meath.
The henge, which could measure up to 200m in diameter, is believed to have been built some 500 years after Newgrange, which dates from 3,000 BC.
The drone that captured the image revealing the henge's presence belongs to historian and author Anthony Murphy, who has been recording and writing about the Boyne Valley for many years.
He said “the weather is absolutely critical to the discovery of this monument. I have flown a drone over the Boyne Valley regularly and have never seen this.”
Mr Murphy said the bit of moisture left in the soil “lodges in the archaeological features a little bit more than it does in the surrounding soil and the crop that is growing out of the soil is greener in the archaeological features and drier outside of them.”
“So when that crop is harvested all surface traces of this monument will vanish and we may not see this monument again for 2 or 3 decades depending on when we get another prolonged dry spell like this.”
Archaeologist Dr Geraldine Stout, who has written about henges, said: "I believe Newgrange is just the centre of a much larger sacred landscape and I think there was a whole series of facilities built for the pilgrims coming to Newgrange in prehistory."
“Generally we believe these henge monuments were built up to 500 years after the main use of Newgrange and in a lot of cases they actually enclose the area of monuments.”
There is no public access to any of the lands close to the henge as they are in private ownership.
In a statement, the National Monuments Service, which is part of the Department of Heritage, said it had just been made aware of the discovery.
It said the quite “extraordinary dry weather conditions of recent weeks and the increasing deployment of drones for aerial photographic use is producing some remarkable discoveries such as this one.
“The National Monuments Service will now be doing some further technical work to help determine the nature of the site, but from the drone images visible on social media, it is a very significant find which fits within the knowledge of large prehistoric ritual enclosures and associated ritual landscapes as at Brú na Bóinne. The National Monuments Service would like to thank Anthony Murphy for reporting this discovery to us.”