Tonight · August 15, 2026

Tonight a Crescent Moon Slips Below Venus, With Earthshine at Its Best

Tonight, as soon as the Sun is under the horizon, two objects will come out of the twilight almost together, low in the west-south-west. Venus first, at magnitude −4.47 : no star comes close, and plenty of people mistake it for an aircraft on approach. Then, six and a half degrees lower and slightly to its right, a crescent Moon lit to 11.9 %.

The scene is lovely and it is short. The Sun sets at 21:06, the Moon sets at 22:01 and Venus at 22:24. In practice everything happens between 21:10 and 21:55: earlier, the sky is too bright; later, the pair is too low.

The two quarter-hours that matter

Civil twilight ends at 21:40, and that is the best moment of the evening: the sky background has darkened enough for the crescent to stand out, and the Moon still has three degrees of altitude left. Fifteen minutes later it is grazing the horizon.

Tomorrow evening the Moon will have crossed to the other side

The Moon moves about thirteen degrees a day across the sky. Tonight it sits to the right of Venus and well below it; tomorrow, Sunday the 16th, it will have crossed to the left, almost level with it, and its crescent will have thickened to 19.6 %. The separation stays in the same range: 6.6° at 21:10, 6.9° at 21:55.

So the two evenings are worth the same, and they do not show the same thing. Tonight the crescent is thinner and the earthshine cleaner. Tomorrow the pair sits higher, which makes it easier from a town garden. The true geometric minimum separation, 2.2°, falls between the two, on the 16th at 07:48 in the morning, in broad daylight and therefore invisible: exactly the sort of figure a headline will quote without mentioning that nobody can see it.

Earthshine: why tonight, and not in ten days

Look at the unlit part of the crescent. It is not black: a faint ashen disc shows through, and in binoculars it is frankly obvious. That glow has a name, earthshine, and a simple cause: the Earth is lighting the Moon.

The effect is measurable, and it is large. Tonight the Moon is 381,582 km away: from its surface, the Earth spans 1.91° of apparent diameter, against 31.3′ for the Moon seen from here. A ratio of 3.7 in diameter, so 13.4 in area. Add that the Earth returns about 31 % of the light it receives against 11 % for the Moon, according to the NASA fact sheets, and tonight’s lunar sky holds an object delivering on the order of 37 times what our full Moon gives us.

And the phases are exactly complementary: while we see a crescent lit to 11.9 %, an observer standing on the dark side of the Moon would see an Earth close to 88 % full. That is why earthshine is spectacular on thin crescents and invisible at first quarter: the fuller our crescent grows, the thinner the Earth becomes in the lunar sky, and the more the lit limb overwhelms the contrast. The useful window is a few evenings a month, and we are in one.

How to see it, and how to photograph it

To the naked eye you need a clear western horizon and a little patience: earthshine appears once the sky background gets darker than it is, so nearer 21:30 than 21:10. Binoculars reveal it at once, with the great lunar seas drawn in grey on grey.

In photographs the difficulty is the brightness gap between the crescent and the ashen part. A phone in night mode, propped on a ledge or a small tripod, overexposes the crescent but brings out the earthshine very well. With a camera, reckon on one second at f/4 and ISO 800 on a telephoto: the crescent will burn out, and that is the price of seeing the Earth.

And what is Venus showing tonight?

Something almost nobody suspects: Venus has phases, like the Moon. Tonight it is 101.9 million kilometres away, its disc measures 24.5 arcseconds, and it is 48.4 % lit. A half Venus, then, at its greatest elongation of 45.9° from the Sun, which falls today. Steadily held binoculars are sometimes enough to suspect it; a small refractor settles the matter, and it is precisely the observation that finished convincing Galileo that the planets go round the Sun.

To place both objects from your exact position tonight, the SkyChart sky map recomputes altitudes and azimuths for your latitude. And if your western horizon is blocked, the night is still worth having: the Perseids are still running, in a sky that goes fully dark from 23:14, as we set out the day before yesterday.

The limits of these figures

Altitudes, azimuths and separations are topocentric, computed for Paris and corrected for standard refraction; allow a few minutes of difference per hundred kilometres. The figure of 37 for the ratio of earthlight to moonlight is an order of magnitude, not a photometric measurement: it combines an exact ratio of apparent areas with a ratio of Bond albedos taken from the NASA fact sheets, which varies with the day’s cloud cover on Earth. And none of this contains any weather, which at seven degrees of altitude remains the deciding factor.

• Earthshine
• Venus
• August 2026 sky