![]() ![]() That means during cold months, when we are closest to the Sun, we are sweeping fastest through our orbit in space. And the closer a celestial body is to the Sun, the faster it must move in its orbit-gravity insists upon that, that’s a fundamental, natural law that was demonstrated 400 years ago by the astronomer, Johann Kepler. We are 3.1 million miles closer to the Sun (called perihelion) in early January, as compared to early July, when we are farthest (called aphelion). It goes back to Earth’s elliptical orbit again, as mentioned above. So why, you might ask, are the “warm seasons” (spring and summer), longer than Winter is the shortest astronomical season, and with its seasonal duration continuing to decrease, it is expected to attain its minimum value - 88.71 days - by about the year 3500. Summer is gaining the minute lost from spring, and autumn is gaining the half a minute lost from winter. However, spring is currently being reduced by approximately one minute per year and winter by about one-half a minute per year. The current seasonal lengths for the Northern Hemisphere are (approximately):Īs you can see, the warm seasons, spring and summer, combined are 7.584 days longer than the colder seasons, fall and winter (good news for warm weather admirers!). Second, the pull of gravity from the other planets also affects the location of Earth in its orbit. Since the seasons are defined as beginning at strict 90-degree intervals, these positional changes affect the time the earth reaches each 90-degree location in its orbit around the sun. Earth’s elliptical orbit is changing its orientation (skew), which causes the its axis to constantly point in a different direction, called precession.A year is not an even number of days and neither are the seasons.There are a few reasons why seasonal dates can vary from year to year. Thus, thanks to atmospheric refraction, the length of daylight on any given day is increased by approximately six or seven minutes. Put in another way, when you watch the Sun either coming up above the horizon at sunrise, or going down below the horizon at sunset, you are looking at an illusion - the Sun is not really there, but already below the horizon.Īs a result, we actually end up seeing the Sun for a few minutes before its disc actually rises and for a few minutes after it has actually set. However, our atmosphere acts like a lens and refracts (bends) its light above the edge of the horizon. If Earth was a planet that did not have an atmosphere, then yes, on the equinox days the length of the day and night would be exactly even. ![]() The reason this happens can be attributed to our atmosphere. In fact, our tables tell you that on the days of the spring and fall equinox, the length of daylight is actually longer than darkness by several minutes. Yet, if you check the calendar pages in our Almanac, you will find that this is not so. We have been taught that on the first days of spring and autumn, the day and night are equal to exactly 12 hours all over the world. After the vernal equinox, the direct rays of the Sun migrate north of the Equator (with hours of daylight steadily growing longer) until they finally arrive at the Tropic of the Cancer (latitude 23.5 degrees north).Ī question revolving around the vernal equinox concerns the length of day versus night. The vernal equinox marks the turning point when daylight begins to win out over darkness.Īt this moment, the direct rays of the Sun are shining down on the equator producing the effect of equal day and night (give or take a few minutes, see below). So what does that mean? Essentially, our hours of daylight-the period of time each day between sunrise and sunset-have been growing slightly longer each day since the winter solstice in December, which is the shortest day of the year (at least in terms of light).Įven though we know that after December 21st, the days start getting steadily longer, we still see more darkness than light over the course of a day in those three months leading up to spring. Vernal translates to “new” and “fresh,” and equinox derived from the Latin aequus (equal) and nox (night). Regardless of what the weather is doing outside, spring equinox marks the official start of the spring season. In 2020, spring fell on March 19th, the earliest first day of spring in 124 years! Traditionally, we celebrate the first day of spring on March 21, but astronomers and calendar manufacturers alike now say that the spring season starts on March 20th, in all time zones in North America. For those of us in the Northern Hemisphere, this was marked by the arrival of the Vernal Equinox (otherwise known as the “First Point of Aries“). The first day of spring is Monday, March 20, 2023, at 5:24 p.m. ![]()
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