Mississippi State University Weather

Meteorological vs. Astronomical Winter

Astronomical winter starts on December 21st, but for meteorologists, it started on December 1st.

Seasons for meteorologists and climatologists are grouped into time periods of three months. This is based on the annual temperature cycle as well as the calendar. For example, meteorological winter lasts from the beginning of December through the end of February. Seasons are grouped this way because it would be more accurate for weather observations, forecasting purposes, and recording climatological data (NCDC, 2013). Meteorological seasons also have a more consistent length. During a non-leap year, fall and winter are approximately 90 days, whereas spring and summer are about 92 days. The consistency of the climatological records since meteorological seasons first started taking place in the mid-1900s have helped with many industries across the United States, such as agriculture and commerce.

According to the National Climatic Data Center, the natural rotation of the Earth revolving around the Sun forms the astronomical calendar and its seasons (2013). The seasons can last anywhere from 89-93 days, depending on the Earth’s rotation. The astronomical calendar has two solstices and two equinoxes. The solstices, which occur in winter and summer, note when the Earth’s equator is farthest from the Sun. The equinoxes, which occur in spring and autumn, note when the Sun is directly over the Earth’s equator. For example, the winter solstice in the Northern Hemisphere is when the Sun’s path is the farthest North it can be from the Earth’s equator (NCDC, 2013). However, the astronomical seasons are opposite in the Southern Hemisphere. When it is winter in the United States, it is summer in Australia.

winter

The astronomical seasons also determine the length of day. For example, because the Northern Hemisphere and the Sun are so far apart during the Winter Solstice, the length of days near the middle of December are much shorter. In addition, the annual temperature cycle is based off of the astronomical seasons; because of this, meteorological winter and astronomical winter are usually separated by about three weeks.  ~ Scott Sincoff

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Works Cited:

National Climatic Data Center, 2013: Meteorological Versus Astronomical Summer—What’s       the Difference?. National Climatic Data Center. National Oceanic and Atmospheric       Administration. Web. https://www.ncdc.noaa.gov/news/meteorological-versus-      astronomical-  summer%E2%80%94what%E2%80%99s-difference.