The length of nighttime hours varies throughout the year due to the position of the Earth in relation to the sun. As the seasons change, the number of daylight and nighttime hours shifts. So what month specifically do nights start to get longer? The answer lies in understanding the relationship between Earth’s orbit around the sun and its tilted axis.
Earth’s Tilt and Orbit Around the Sun
Earth is tilted on its axis by 23.5 degrees relative to the plane of its orbit around the sun. This tilt is what causes the seasons. As Earth revolves around the sun over the course of a year, its tilted axis always points in the same direction. So sometimes the Northern Hemisphere is tilted towards the sun, and other times it is tilted away. Here’s a more detailed explanation:
- During the Northern Hemisphere summer, the northern axis is tilted towards the sun. This means the Northern Hemisphere receives more direct sunlight and longer days.
- During the Northern Hemisphere winter, the situation is reversed. The northern axis tilts away from the sun, resulting in less direct sunlight and shorter days.
The amount of daylight continues to shift from season to season as Earth maintains its tilted orientation circling the sun. So when exactly does this transition to shorter days begin?
Nights Start Getting Longer in June
In June, the Northern Hemisphere is tilted maximally towards the sun marking the summer solstice. This corresponds with the longest day and shortest night of the year. For example, in New York City, the summer solstice yields about 15 hours and 5 minutes of daylight. After the solstice in late June, the number of daylight hours gradually begins to decrease as the Northern Hemisphere starts tilting away from the sun.
Therefore, the nights start getting longer beginning in the month of June for the Northern Hemisphere. The further we progress from the June solstice, the more noticeable the shorter days become. By September, daylight hours are significantly reduced compared to the peak days of June. Below is a table showing this progression using New York City as an example:
| Month | Hours of Daylight |
|---|---|
| June 21 (Summer Solstice) | 15 hours 5 minutes |
| July | 14 hours 45 minutes |
| August | 13 hours 49 minutes |
| September | 12 hours 30 minutes |
The Effect of Latitude
The exact day/night lengths vary depending on latitude. Locations at higher latitudes in the Northern Hemisphere will experience even more extreme contrasts over the course of the year. For example, Helsinki, Finland at 60°N latitude has nearly 19 hours of daylight at the summer solstice in June, but only about 5.5 hours in December. Contrast that with Quito, Ecuador which is near the equator and experiences roughly 12 hours of daylight year-round.
High Latitude Locations
At higher Northern Hemisphere latitudes:
– Summer days can last up to 20+ hours
– Winter days can be as short as 4-5 hours
– Nights can begin getting longer as early as late April/May after the early summer solstice
Low Latitude Locations
At lower Northern Hemisphere latitudes closer to the equator:
– Day length varies only 1-2 hours over the course of the year
– Nights get longer only slightly after June solstice
The Southern Hemisphere
Everything is flipped in the Southern Hemisphere due to the opposite orientation relative to the sun. When the north is tilted towards the sun in June, the south is tilted away resulting in its winter season. Therefore, for the Southern Hemisphere, the June solstice marks the longest night and shortest day of the year. So for locations south of the equator, nights get longer starting in June.
The Vernal and Autumnal Equinox
On the autumnal equinox around September 22, day and night are approximately equal in length around the globe. This marks when the Northern Hemisphere transitions from summer to fall. After this point, nights continue to lengthen until the winter solstice in December.
The vernal equinox in March is the midpoint transitioning from winter to spring when day and night are again roughly equal. For the Northern Hemisphere, nights continue to shorten from this point forward culminating in the longest day of the year in June.
Conclusion
To summarize, the key points are:
- Earth’s tilted axis causes seasons as it orbits the sun
- In the Northern Hemisphere, nights start getting longer in June after the summer solstice
- The effect is more extreme at higher latitudes further from the equator
- The pattern is opposite south of the equator in the Southern Hemisphere
- Equinoxes in March and September mark equal day/night around the globe
So if you notice your evening stroll getting a little darker in the early summer, you can now attribute it to Earth’s seasonal progression as it makes its yearly journey around the sun. Next time you wonder “what month do nights get longer?”, you’ll know the answer points to June in the Northern Hemisphere.