Vernal

The Spring Equinox 2021 is about to happen on March 20. Equinox has its own unique identity for celebration time, dates, images, wallpapers, rituals, and more about Spring Equinox and Autumnal Equinox. The Spring or Vernal refers to Spring season that comes after Winter season and before Summer. In the other hand the definition of spring varies according to the local climate, culture and customs. In Spring season the days becomes longer and weather gets warmer in the temperature zone. Because the Earth tilts its orbital plane around the Sun. It is the season when flowers blooms and plant grow.

Spring Equinox 2021

Equinox is the instant of time when the plane of earth’s equator passes through the center of the sun. This occurs twice each year around 20th march and 23rd September. In other words it is the moment in which the sun is directly above the equator.

Equinox is derived from Latin word which means “equality of day and night”. On the day of an equinox daytime and nighttime have similar but not quite equal lengths. This has everything to do with the way our planet moves. Earth’s axis is tilted at a 23.5 degree angle relative to the plane of its orbit around the sun.

An equinox marks the exact moment when the sun enters an imaginary line in the sky. This invisible ring around the Earth sits directly above the equator. Scientist called this ring the Celestial equator. It is a line the sun only crosses twice a year, on the spring and autumn equinoxes. Due to that solar angle, every region of our planet will experience close to 12 hours of daylight and 12 hours of darkness.(Technically the daytime is going to last a few minutes longer than the nighttime)

Spring Equinox

According to the Northern Hemisphere the March Equinox is also known as Spring or Vernal Equinox. Rather according to the Southern Hemisphere the September Equinox is also known as Autumnal Equinox or Fall Equinox. The word Vernal or Spring Equinox is combination of two words “the Vernal/Spring” and “The Equinox”.

Equinox Time for Upcoming Years:

An Equinox refers to the time or date at which the sun crosses the celestial equator. It happens twice in each year. During the equinox the day and night are equal in length. The Equinox happens in March 20, and September 23 of each year. In other hand, the experts says that when equinox comes the Earth passes the equator through the center of the Sun. In the equinox time the center of the visible Sun is directly above the equator.

Spring Equinox YearDateTime
202020 March3:50 AM
202120 March9:37 AM
202220 March15:33 PM
202320 March21:24 PM
202420 March3:07 AM
202520 March8:54 PM
Autumnal Equinox YearDateTime
202022 September13:31 PM
202122 September19:21 PM
202223 September01:04 AM
202323 September06:50 AM
202422 September12:44 PM
202522 September22:18 PM

EQUINOXES ON EARTH

The equinoxes are the only times when the solar terminator is perpendicular to the equator. As a result, the northern and southern hemispheres are equally illuminated. For the same reason, this is also the time when the Sun rises for an observer at one of Earth’s rotational poles and sets at the other; for a brief period, both North and South Poles are in daylight. This is possible because atmospheric refraction “lofts” the Sun’s apparent disk above its true position in the sky.

Spring Equinox - Vernal Equinox

Systematically observing the sunrise, people  discovered that it occurs between two extreme locations at the horizon and eventually noted the midpoint between the two. Later it was realized that this happens on a day when the durations of the day and the night are practically equal.

VERNAL EQUINOX

In the northern hemisphere the spring or vernal equinox happens around march 21, when the sun moves north across the celestial equator. It marks the beginning of spring in northern hemisphere and autumn in the southern hemisphere. It is considered the start of New year in Assyrian calendar, Hindu and Persian calendars or Iranian calendars as Nowruz (New day).

DATE OF SPRING EQUINOX

According to Julian calendar 25th march was the date of spring equinox, which was already the starting day of the year in the Persian and Indian calendars. As Julian year is longer than the Tropical year by about 11.3 minutes on average, the calendar drifted with respect to the two equinoxes. So in AD 300 spring equinox occurred on 21st march and by AD 1500 it had drifted backwards to 11th march.

Due to this drift the Pope Gregory XIII create the modern Gregorian calendar. The pope wanted to continue to coincide with the edicts of the Council of Nicaea in AD 325 concerning the date of Easter, which means he wanted to move the vernal equinox to the date on which it fell at that time (21 March is the day allocated to it in the Easter table of the Julian calendar). He also wanted to maintain it around that date in the future and to achieve this he reduced the number of leap years from 100 to 97 every 400 years.

However there remained a small variation of ±27 hours from its mean position because the distribution of 24 hour centurial leap days causes large jumps. This raises the possibility that it could fall on 22nd march and the Easter day might theoretically start before the equinox. To swing the equinox from 19th to 21st march, the astronomers choose appropriate number of days to omit.

AUTUMNAL EQUNIOX

Autumnal equinox occurs around 22nd September, when the sun crosses the Celestial equator going south. It marks the beginning of autumn in northern hemisphere and spring in southern hemisphere.

Autumnal Equinox

NAMES OF BOTH EQUINOXES

Vernal and autumnal

These are historically universal and most widely used names for equinoxes. They are derived from Latin, vernal means spring and autumnal means autumn. Beside they are widely used but they are confusing as in southern hemisphere the vernal does not occur in spring and the autumnal does not occur in autumn. The terms spring equinox and autumn equinox of common English are used to overcome this confusion.

March equinox and September equinox

These names refer to the month of the year in which they occur, with no uncertainty as to which hemisphere is the context. As not all cultures use solar-based calendar where the equinox occur every year in the same month(as they do not in the Islamic calendar) that’s why these names are not universal. Though the terms have become very common in 21st century.

Northward equinox and southward equinox

The march equinox occurs when sun crosses when the sun crosses the equator from south to north, that’s why it is also known as Northward equinox. The Southward equinox occur in September when sun crosses the equator from north to south. These terms can be used clearly for other planets.

EFFECT OF EQUINOX ON SATELLITES

Temporary disruption of communication satellites is the major effect of equinoctial period. There are few days around the equinox when the Sun goes directly behind the satellites(geostationary satellites)relative to Earth, for a short period each day. The sun has more powerful radiations than Earth and the spectrum of these powerful and immense radiations overload the Earth station’s reception circuits with noise. Moreover depending on antenna size and other factors these radiations temporarily disrupt or degrade the circuit. The duration of these effects varies from few minute to an hour. For example, for a given frequency band, a larger antenna has a narrower beam-width and hence experiences shorter duration.

During equinoctial period the geostationary satellites have to travel through Earth’s shadow and rely only on battery power due to which they experience difficulties in maintaining power. Usually, a satellite will travel either north or south of the Earth’s shadow due to its shifted axis throughout the year. During the equinox, since geostationary satellites are situated above the Equator, they will be put into Earth’s shadow for the longest duration all year.

EQUINOXES ON OTHER PLANETS

Equinoxes occur on any planet with a tilted rotational axis. One example is Saturn, where the equinox places its ring system edge-on facing the Sun. As a result, they are visible only as a thin line when seen from Earth. A view seen during an equinox for the first time from the Cassini space probe in 2009 – they receive very little sunshine, indeed more planet shine than light from the Sun. This phenomenon occurs once every 14.7 years on average, and can last a few weeks before and after the exact equinox. Saturn’s most recent equinox was on 11 August 2009, and its next equinox will take place on 6 May 2025.

The equinoxes also occur on mars and the most recent equinox on mars was on 23rd march, 2019 (northern spring). The next equinox on mars will be on 8th April 2020 (northern autumn).

Reviewed by; Hina Himat