Sunrise and sunset are daily phenomena that can be enjoyed forever. Taking for granted, you are rarely interested in what algorithm the movement of the celestial body occurs, which affects the trajectory of why unusual things happen: polar days and nights, northern lights or eclipses.
The emergence of sunset and sunrise of the heavenly body
The earth is in constant motion both around the sun and around its axis. Once a day, with the exception of the polar latitudes, one can observe how a ball of fire disappears beyond the horizon and reappears there every other day, but on the other side. Sunrise and sunset is the time when the “burning” disk of the celestial body disappears from the field of view, and the extreme upper point is completely hidden or appears (at the time of dawn).
There is a concept of the “border of day and night”. This parameter significantly affects the zenith. The latter means a line directed from a point to the surface of the earth perpendicular to it. The zenith angle is the distance between the direction of the beam towards the center of the earth and the vertical. Depending on the size of the angle, it can be said whether the sun has fully risen. The same thing defines the end of twilight and the beginning of night.
In astronomy there is the concept of twilight:
- For high latitudes in winter and summer, the sun may not set or rise. Twilight is considered zero.
- The length of the day in such latitudes will be indicated either 24 hours or 00 hours.
- Twilight lasts from 15-25 minutes in different parts of the earth.
The conclusion follows: twilight has a beginning and an end. Their duration depends on the position of the sun at sunset. If the earth did not have an atmosphere, and the sun was a point, the zenith angle would be 90 degrees. Since the sun has no angular diameter, light is reflected by solid particles. Therefore, the upper edge of the disk depends on the movement of the center of the star. In a normal atmosphere, an angle of 90 degrees is converted into a straight line in 50 minutes. Accordingly, if sunset would begin by decreasing the right angle, twilight would last longer.
As soon as the sun disappeared beyond the horizon, the second stage of twilight begins - a civilian appearance. The zenith angle is less than 96 degrees to the opposite side of the hemisphere. Further, the angle increases to 102 degrees. These are nautical twilight. Still light, the horizon line visible on the water. Then comes the astronomical twilight: the angle is 108 degrees, and the visibility of objects becomes weak.
Important! Such calculation algorithms are not suitable for those cities where time does not give way to summer and winter. Also, the result will not be true, for example, for New Zealand. Summer time is valid from May to September. Therefore, the time of sunrise and sunset is different everywhere.
Why does the sun turn red?
Sunrise and sunset create an optical effect. The sun's rays illuminate the earth's surface, painting the sky in different colors. At dawn we see more delicate shades of red, yellow. At sunset, red and burgundy colors predominate.
The fact is that by evening the surface of the earth warms up, humidity decreases, and the speed of air flows increases. The difference in color scheme depends on the area:
- On flat terrain, the sunset will not be so saturated.
- Along the coastline - brighter.
- And in the northern latitudes - more colorful, but not so bright.
The sun's disk is far from the horizon. Rays are reflected from the surface. In the western part of the horizon, the colors are not so bright. They are orange, red or yellow.
The closer to the horizon, the more red we see. On either side of it is a golden edge. The dawn is visible above the dawn. On the other side of the earth, a bluish tint appears in the sky. This is the shadow of the earth. Above it, a segment of the sky is painted in ashen color - the Belt of Venus. Occurs over the horizon at a level of 10 to 20 °.
Interesting! The red rays of the sun are the longest, they are noticeable even at sunset. Yellow and white rays are the shortest, so they are not visible when the sun sets over the horizon.
How does the moon phase affect?
The moon does not always appear as a full disk. At first it looks like a crescent, then it starts to increase. When it becomes full again, it decreases. This process affects several phases, forming a cycle of 29.5 days in length:
- The first phase - the area of the illuminated disk is less than half the entire disk of the moon.
- The second phase is the end of the new moon and the transition to the full moon.
- The third phase is characterized by the appearance of a full disk.
- The fourth phase is the final stage of the full moon, turning into a new moon.
Sunrises and moons are interconnected. The surface of the satellite reflects sunlight, showing the amplitude of motion around the Earth.
Calculation of sunrise and sunset
To calculate when the sun rises and sets, astronomical physicists use a formula taking into account the declination of the celestial body. The latitude value can be found on the world map, and the pole height - according to geographical latitude (one value).
For instance:
cos (t) = - (0.0148 + sin (f) * sin (d)) / (cos (f) * cos (d)),
- where t is the hour angle
- f is the latitude
- d is the declination.
0.0148 (this is the 51 'sine) is the contribution from refraction and disk size. If it weren’t, the formula would be much more beautiful, on the right side would be: tg (f) * tg (d) *.
So, in the extreme case, when day is equal to night during the solstice, it is obvious: t is 6 hours (90 °), cos (t) = 0. We get a simple equation: sin (f) * sin (-23.5 °) = -0.0148 , whence f = 2.1 ° (approximately). At this latitude, December 21, day is equal to night, that is, 12 hours.
Now you can find out the schedule of sunrise and sunset by downloading a special application, referring to calendar sources. Various calculation options are also available on the Internet, simplified and expanded, taking into account amendments, sun movement and the location of a person. Sunrise and sunset are interesting phenomena, but also, in addition to this, many mysteries remain in the world, the scientific nature of which is divided into the realities of perception of information.
Why is the day length different?
When the front pages of The Quiet Flows the Don appeared information about the time of sunset and sunrise, readers had questions. For example, why is the longitude of the day different from what is stated on the calendars?
Longitude of the day is the period between sunrise and sunset. But it is not always possible to calculate even the approximate time of this process. The fact is that the declination angle of the star has a certain meaning. It affects the seasonal changes in the weather, the longitude of the day. Sunrise and sunset determines how many hours there will be day, how many - night. In winter, the night is longer; in summer, the day.
But geographical latitude affects the duration of daylight hours. The farther from the equator, the shorter the day in winter and the more in summer.
Here is a simple example:
Moscow is located at about 55 about with. w. (northern latitude), the village of Veshenskaya - 49 about with. sh., and Rostov-on-Don - 47 about s. w. The longitude of the day depending on latitude changes as follows: on the same day, January 22, in Moscow it is 8 hours 01 minutes, in Veshenskaya station - 8 hours 54 minutes, and in Rostov-on-Don 9 hours 10 minutes
In summer, the opposite is true: while in the south of Russia at the end of June the longitude of the day is 15 hours, in St. Petersburg it reaches 18 hours, i.e. the farther north, the longer the summer day.
The longest day length occurs on the summer solstice (approximately June 22), and the smallest on the winter solstice (approximately December 22).
As regards calendars, one thing can be said: they mainly print the longitude of the day for a latitude of about 55-56 about . This is the latitude of Moscow. And in the newspaper Tikhiy Don, the longitude of the day is indicated specifically for Veshenskaya. Therefore, the numbers differ.
Interesting facts: polar days, equinoxes, northern lights
In addition to the schedule of sunrise and sunset, the inconsistency of the movement of light rays, there are many interesting facts about celestial bodies. Recently, astronomers decided to show what the Earth looks like from the moon. And so, what happened:
Earthrise is a common thing for guests moon satellite. Did you know that:
- Mars rover Spirit captured the sunset on Mars. He is surprisingly beautiful in blue-gray shades.
- Aurora borealis happens not only on the Earth. On Jupiter, it will be colored purple.
- Polar nights are inevitable in Murmansk. In Alaska, about a ton of large pumpkins grows during the polar days.
- The shortest polar night lasts 2 days (at the latitude of the Northern Hemisphere). The longest is at the South Pole. It lasts almost six months.
All scientific research known to mankind does not cover even 1% of knowledge about space, planets and their behavior in the Universe. What other secrets does the Earth keep, how long will the sun shine, and how much energy does our galaxy have?