While orbiting the sun, a planet revolves around itself. The time it takes a planet to orbit itself once is called a period of rotation. The rotation time of the earth is 23 hours and 56 minutes. Therefore, a day on earth is 24 hours. Only the planets in our solar system can survive on the earth we live on. Because it is at the right distance from the sun, the earth has the right temperature, the right source of water, the right atmosphere, and the ozone layer. Life can continue on earth. Due to the reflection of light on the water and land areas of the earth, when viewed from the sky the earth appears bluish-green.
Fig:1 Elliptical motion of planets
If the time duration of day and night is equal that day is referred to as Equinox. It occurs twice a year. One is on March 20 and another one is on September 22. When the planet's sub polar point crosses through its equator that process is called an equinox. Both Northern and southern hemispheres experience approximately identical time durations of day and night time in an equinox time. The sub polar point and equator are on the same point during the equinox in a year. The earth orbits the earth in an elliptical orbit. So it is a misconception that summer appears when the earth is closest to the sun and winter when it is in decline. Seasons are caused by the earth orbiting the sun at an angle of 23.5°.
These occur twice a year. One is on March 20 and another one is on September 22. These two equinoxes are named the vernal equinox and autumnal equinox. It is also called spring equinox and fall equinox. The earth’s northern hemisphere is farthest from the sun due to its 23.5°tilt, while the southern hemisphere is adjacent to the Sun. So while the northern hemisphere is winter, the southern hemisphere is summer.
The vernal equinox and autumnal equinox happen on different dates for both hemispheres. The equinox that happens in March is the Vernal equinox. The equinox that occurs in September is the autumnal equinox. When the vernal equinox is in the northern hemisphere, the southern hemisphere is in the autumnal equinox. The northern hemisphere is in the autumnal equinox then the southern hemisphere is in the vernal equinox. The solar declination is zero degrees in the time of equinoxes. The earth does not tilt 23.5° towards the sun during the time of equinoxes. This happens only during the equinoxes. The sub polar point and equator are on the same point during the equinox in a year. The sub polar points change their direction before and after the equinox from north or south. The sub polar point moves to the north and the Northern hemisphere tilt towards the sun after the March equinox. The sub polar points move to the south and the Southern hemisphere tilt towards the sun after the September equinox.
The longest day or night time of the year will happen when the sun is too far away from the equatorial plane. This time is called solstice. It happens twice a year. In other words, a pole of the planet is extremely closer or away from the orbit of the star which is orbiting the planet. Equinox does not change the period of day and night. But solstice changes the time duration of day and night. The complete display of daylight is the peak moment of the solstice in the poles. At the same time solstice is marked very rarely in the equator. The sub solar points are marked by solstice when it reaches the north and south most latitudes. The sub solar point will cross all latitudes between north and south latitudes two times a year.
The solstice occurs two times a year. Summer solstice and winter solstice are the two types of solstice. The summer solstice occurs in a year when the time duration of the day is long. The winter solstice occurs in a year when the time duration of the day is shorter. The summer solstice is on June 21 and the winter solstice is on December 22.
The Summer solstice and winter solstice are the seasons of the solstice. Solstice is also known as midsummer and midwinter because it happens in the middle of those seasons.
The longest day of the year is called the summer solstice. The shortest day of the year is called the winter solstice. The summer solstice is on June 21 and the winter solstice is on December 21. During the summer solstice, the intensity of rays from the sun will stay for a long time.
So the time of the daylight will be longer. The Winter solstice has a short time of daylight.
The planets orbit the Sun in a fixed curved orbit. It is elliptical. The time it takes for the planets to orbit the sun once is called the planetary orbit. If the time duration of day and night is equal that day is referred to as Equinox. It occurs twice a year. One is on March 20 and another one is on September 22.
The rotation time of the earth is 23 hours and 56 minutes. Therefore, a day on earth is 24 hours. The longest day or night time of the year will happen when the sun is too far away from the equatorial plane.
This time is called solstice. It happens twice a year. In other words, a pole of the planet is extremely closer or away from the orbit of the star which is orbiting the planet. Equinox does not change the period of day and night. But solstice changes the time duration of day and night.
Q1. Define Newton’s law of Gravitation
Ans: A particle with mass M in the galaxy attracts all particles in the galaxy with a certain force. That gravitational force is directly proportional to the multiplication of its mass and inversely proportional to the square of the distance between them.
$\mathrm{\widehat{F}=-\frac{GM_1M_2}{r^2}\widehat{r}}$
Q2. Describe the planet with the highest temperature among the planets found in the solar system?
Ans: Venus is the hottest planet in our solar system. After the moon, this is the brightest sky visible in the sky. Unlike other planets, which rotate in the opposite direction, the sun rises in the west and sets in the east. We can easily see Venus with the naked eye. It is visible in the lower sky in an east or west direction.
Q3. What is the cosmic year?
Ans: The cosmic year is the time it takes for the earth to orbit the Milky Way galaxy at the speed of 250km/h ( 9 million km/h). This equates to 225 million Earth years.
Q4. What is a polar galaxy?
Ans: Although all galaxies appear to move from east to west, only one is known to be immobile and is called a polar galaxy. The polar galaxy is not visible from the southern hemisphere of the Earth. The polar galaxy appears to be in one place, as it is located directly relative to the Earth’s spiral axis.
Q5. What is microgravity?
Ans: Microgravity is the state in which objects or humans appear to be weightless. Microgravity means very small gravity. When astronauts and a few objects float in space, we can sense the effects of microgravity.
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