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Earth's Climate Timeline

Diurnal Cycle Timeline

Driven by the Earth's spin on its axis, the diurnal cycle of night and day is a powerful driver of variability of weather

Image of Earth spinning on axis (NOAA)

Sunlight hits the surface of the Earth

Image of dawn on Earth from space (NASA)

Mid Morning
Temperatures rise most quickly during mid morning
High Noon
Heated air circulates in bottom 1 km of atmosphere
Image of sun in clouds (NOAA)
Temperatures are hottest during the mid afternoon


Sunlight stops hitting Earth's surface.


Image of moonrise (NASA)
Temperatures fall most quickly around sunset as surface and atmosphere radiate heat

Lowest level of atmosphere becomes cooler.

Middle of the Night
Earth, water surfaces and human communities release stored heat.
Image of lights at night from NGDC/NOAA
Right before Dawn
Temperatures are coldest around dawn

Summary of 1 Year Time Scale

One full orbit around the sun- the period of a year- serves as a fundamental force of climate variability as well as a measure of time. The essential cause of seasonal climate change during the year is the tilt of Earth's axis, currently 23.5 degree tilt off its axis, which alters the angle of solar radiation and thus its intensity over the course of the year

Annual Cycle
Time of Year
Climate Variability
Dec. 21 or 22, shortest day in Northern Hemisphere, longest in Southern
Image of Crater Lake from NPSNorthern Hemisphere tilts away from sun, receiving less direct solar radiation, while the Southern Hemisphere tilts towards the sun.

Blizzards and ice storms can occur throughout the boreal (Northern Hemisphere) winter months in higher latitudes and elevations.
Image of Crater Lake by NPS.
Spring (Vernal) Equinox
March 20 or 21 in Northern Hemisphere

Image of New River from NPSWhen the sun's direct rays pass the equator, the length of day and night are the same. (Equinox means " equal night"). Without sufficient spring precipitation, droughts may occur later in the year as evapotranspiration increases. In regions where winter and spring precipitation falls as snow, runoff peaks start in the Spring in the southern regions and progresses northward and upward in elevation as the season progresses.
Image of New River by NPS

June 21 or 22, shortest day in the Southern Hemisphere, longest day in Northern Hemisphere

Image of Death Valley from NPSNorthern Hemisphere tilts toward the sun, receiving more intense direct solar radiation, while the Southern Hemisphere tilts away from the sun and experiences winter.

In regions where winter and spring precipitation falls as snow, there is often a peak in snow melt runoff around the solstice. Droughts, flash floods, forest fires and hurricanes are all climate-related events that usually occur during the summer months and into the fall.

Wet season during the Indian Monsoon generally begins in June and goes through September.
Image of Death Valley by NPs

(Autumnal) Equinox
Sept. 22 or 23
in Northern Hemisphere

Black Rock Mountain State Park by USFSSun's direct rays pass the equator and length of day and night are the same. The seasonal cooling of the climate during autumn may include the end of the growing season in some climates. Hurricane activity may extend well into the Autumn season.

Image of Black Rock State Park, GA by Tom Wilson, USFS.