There are two opportunities to spot a thin Moon at the start of July 2024, the first in the dawn sky on 5 July and the second in the evening sky on 6 July.
The best time to see these thin Moons will be 5 July, approximately 40 minutes before sunrise or 6 July, approximately 30 minutes after sunset.
A thin crescent Moon is one that occurs immediately before or after new Moon.
In order to be seen at all, the timing has to be just right to place a Moon which is greater than the Danjon limit within evening or morning twilight.
The Danjon limit states how far the Moon needs to be away from the Sun to be seen.
The Moon isn’t perfectly smooth; its rough surface is littered with craters, mountains and valleys that break up the thin arc of light close to new Moon and limit its visibility.
The Danjon limit states that the Moon needs to be more than 7° from the Sun to be seen.
Another factor is sky brightness.
A fuller phase of Moon is easy to see in a dark sky, but a very thin crescent is in itself less bright and it appears in a sky that’s in bright twilight. This creates a major visibility challenge.
Then there’s the weather. The slightest bit of haze will do a very impressive job of hiding a thin Moon.
Put all of these hurdles together and you’ll understand that grabbing a view or a photograph of a very thin Moon is something of a rarity and quite an accomplishment.
If the weather is good, we’d recommend following the ever-thinning waning Moon in the morning sky from 1–4 July to get a feel for how it looks before the big event on the morning of 5 July.
The thin Moon on 6 July will be close to Venus and Mercury, but it will be tough to spot. As ever, never look using optical aids, unless the Sun is below the horizon.
If you manage to observe or photograph the thin Moon, let us know by emailing contactus@skyatnightmagazine.com
This guide appeared in the July 2024 issue of BBC Sky at Night Magazine
