Why the New Crescent Leans: Its Tilt and Height by Latitude and Season

The Short Answer

The young crescent does not look the same from everywhere, or in every month. Its tilt and its height at sunset are both set by one angle: how steeply the ecliptic, the Sun's path across the sky, meets the western horizon. That angle depends on your latitude and on the date.

On the evening after the new moon of 6 February 2027, a Moon 24 hours old is a nearly perfect bowl at 30° N (tilted 9° from a bowl), leans 27° at 45° N, and stands almost on its end at 45° S (75°). Over the year, at 45° N the same 24-hour-old Moon averages 9.9° high at sunset in March but only 2.7° in October. At 45° S the seasons are swapped. On the equator it stands about 10° high all year.

Every comparison here uses the same Moon age, 24 hours after conjunction, so the differences come from the sky and the season, not from an older or a younger Moon.

Why a Crescent Leans

The Sun and the Moon travel along almost the same line. The Sun follows the ecliptic, and the Moon stays within about 5° of it. The bright side of the crescent always faces the Sun. Twenty-four hours after the new moon, the Moon is about 12° from the Sun, further along the ecliptic. So the line from the Moon to the Sun runs along the ecliptic, and the tilt of the crescent follows the angle the ecliptic makes with the horizon.

• If the ecliptic meets the western horizon steeply, the Moon stands almost straight above the point where the Sun has set. The Sun is directly below the Moon, so the bright side faces down: the crescent is a bowl, a smile resting above the horizon.
• If the ecliptic meets the horizon at a shallow angle, the Moon stands to one side of the Sun and only a little higher. The bright side faces sideways: the crescent stands on its end, like the letter C.

To a first approximation the tilt from a bowl is 90° minus the ecliptic's angle with the horizon, give or take a few degrees, because the Moon is not exactly on the ecliptic. The height follows the same rule: a steep ecliptic lifts the Moon almost the whole 12° it is away from the Sun, and an ecliptic at 22° lifts it only about a third of that (the sine of 22° is 0.37).

How steep the ecliptic is at sunset depends on the latitude and on where the Sun is on the ecliptic, which is the season. Over a year the angle swings between 90° minus the latitude minus 23.4° and 90° minus the latitude plus 23.4°, where 23.4° is the tilt of the Earth's axis. We measured it at sunset on the equinoxes and solstices of 2026:

At 45° N the ecliptic is steepest around the March equinox (68°) and flattest around the September equinox (22°). In the Southern Hemisphere it is the other way round. On the equator it never drops below 66.6°, so the Moon is always close to straight above the Sun there.

One Evening, Six Latitudes

The figure shows one Moon from six places. It is 24 hours after the new moon of 6 February 2027, and each crescent is seen from the spot on its line of latitude where the Sun is setting at that moment (15:56 UTC on 7 February). The height above the horizon line is to scale. The size of the Moon and the thickness of the crescent are exaggerated: a real 24-hour-old crescent lights about 1 per cent of the disc.

Three things stand out:

• The tilt grows away from 30° N. It is 9° there, 27° at 45° N and 51° at 65° N. To the south it is 25° on the equator, 58° at 30° S and 75° at 45° S.
• The height changes just as much. The Moon is 9.2° high at 30° N and only 2.1° high at 45° S, on the same night and 24 hours after the same conjunction. In early February the ecliptic meets the sunset horizon steeply at 30° N and at a shallow angle at 45° S.
• The lean is mirrored. For an observer facing west, the Sun sets to the right of the Moon in the northern drawings and to the left in the others, and the bright side leans toward the Sun. At 45° N the Sun is on the right in every month of the year, and at 45° S on the left.

The Seasons

Now the whole year. For each of the 619 new moons from 2000 to 2049 we found the Moon 24 hours after conjunction, seen from the place on the latitude where the Sun is setting at that instant, and averaged by month.

At 45° N the average height of the Moon at sunset is 9.9° in March and 2.7° in October. The band shows how much single evenings vary: in March, 80 per cent of the evenings fall between 6.9° and 11.9°. In October they run from 1.2° below the horizon to 7.2° above it, so on at least one October evening in ten the Moon has already set before the Sun. At 45° S it is the same curve shifted by six months: 9.9° in September, 2.8° in March. In February, when Ramadan 1448 begins, the average is 9.0° at 45° N and 3.4° at 45° S.

The high, bowl-shaped crescents come in the spring of each hemisphere: February to May at 45° N, August to November at 45° S. The low, upright ones come in the autumn. On the equator there is no good or bad season: the height stays between 9.7° and 10.6° and the crescent stays close to a bowl.

A Hijri month does not stay in one season. It falls about 11 days earlier in the Gregorian year each year, so it passes through all the seasons in about 33 years. No month is permanently the easy one or the hard one for a given latitude.

What This Does and Does Not Tell You

• These are averages at a fixed age. A real first evening finds the Moon anywhere from newly born to about 30 hours old, depending on your longitude and on the month. The 24 hours is there to compare seasons fairly, not to describe any one sighting.
• The altitudes are geometric. They leave out refraction, which makes the Moon look about half a degree higher near the horizon.
• Tilt is geometry, not visibility. The visibility criteria on this site, Yallop and Odeh, work from the Moon's height above the Sun and the width of the crescent. Neither uses the tilt. Height matters because it sets how much sky and haze the light crosses, and this is where season and latitude do make a real difference.

Check Your Own Sky

Open the Sky Dome at sunset on the first evening of a month and compare the Moon's position with the horizon, then look at the visibility map for the same evening to see how the zones change with latitude. The calendar page shows which evening to look on.

Frequently Asked Questions

Why is the crescent a bowl in the tropics?

Because the ecliptic is steep at sunset all year there: between 67° and 90° on the equator. The Moon stands almost straight above the setting Sun, so the Sun is directly below it and the bright edge faces down.

Is the crescent upside down in the Southern Hemisphere?

No. A bowl is a bowl on both sides of the equator. What differs is which way the bright side leans: for an observer facing west it leans toward the Sun, which is on the right of the Moon at northern latitudes and on the left at southern ones. On the equator it changes with the season: on most evenings from January to June the Sun is to the left of the Moon, and from July to December to the right.

Which season gives the highest new crescent?

The spring of your hemisphere, when the ecliptic is steepest at sunset: roughly February to May in the north at mid-latitudes, and August to November in the south. Near the equator the height hardly changes.

Does a more upright crescent mean it is easier to see?

Not by these numbers. A higher Moon is generally easier because the light passes through less of the thick air near the horizon, but the tilt itself is not part of the criteria. A 24-hour-old Moon that is 10° up in March at 45° N and one that is 3° up in October are both 24 hours old, and the second is much harder to find.

Why is the Moon sometimes below the horizon at sunset even though it is 24 hours old?

Because 24 hours of age is not a height. If the ecliptic lies nearly flat on the horizon, the Moon, 12° from the Sun along it, can be level with or below the horizon. This is why the autumn evenings at mid-latitudes are the hardest.

See Also

• The science behind the crescent
• What is the hilal?
• Why the crescent is visible in some countries and not others
• Why the Moon's path across the sky changes every month
• The annular eclipse of 6 February 2027
• The Moon's 18.6-Year Cycle, and Why Northern Autumn Crescents Hug the Horizon Until the Early 2030s
• The Crescent and the Star: When the Young Moon Meets Venus or Jupiter, Every Evening to 2030

References

• Meeus, J. (1998). Astronomical Algorithms (2nd ed.). Willmann-Bell. Chapter 14 covers the angle between the ecliptic and the horizon.
• The numbers and the charts in this post are reproduced by docs/research/crescent-tilt-season.mjs, and computed by packages/astronomy/src/crescentSeason.ts, in the Hilal Vision source.