1. How can you navigate by the stars?
You can navigate using bright stars. Navigation stars are the 26 brightest stars used for orientation. They indicate directions to certain sides of the horizon. Eg, polar Star always points towards North.
2. What is the Solar System? Which cosmic bodies are included in it?
The solar system is the Sun and the cosmic bodies moving around it. Part solar system enters the Sun and cosmic bodies moving around it (planets, satellites, comets, asteroids), interplanetary space with tiny particles and liquefied gas.
3. What is the orbit of a planet? What shape do the orbits of the planets in the solar system have?
Orbit is the path of a planet around the Sun. The orbits of the planets of the solar system are shaped like ellipses.
4. Which planet from the Sun is the Earth? Between which planets is it located?
Earth is the third planet from the Sun. It is located between Venus and Mars.
5. What groups are the planets of the solar system divided into? How are the planets in these groups different?
The planets of the solar system are divided into planets terrestrial group and giant planets. They differ in composition and size. Terrestrial planets are rocky and have small sizes. Giant planets have a gas-dust composition and are large in size.
6. How does the Sun affect the Earth?
The sun attracts the Earth and is responsible for its movement. It supplies the Earth with heat and light, which affects living organisms. Solar radiation influences the Earth's magnetic field.
7. Name the planets of the solar system. Which ones are received from the Sun? more light and heat than the Earth, and which ones are less?
Planets of the Solar System - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Mercury and Venus receive more light and heat than Earth. All other planets receive less heat and light compared to Earth.
8. What is called a day? What is the length of one earthly day? Under what conditions can the day become longer or shorter?
24 hours – natural, given by nature basic unit of time. The length of an earthly day is 24 hours. The length of the day can change when the speed of the Earth’s rotation around its axis changes: increasing the rotation speed will shorten the day, slowing it down will increase it.
9. What are geographical consequences rotation of the Earth around its axis?
Rotation around its axis affects the shape of the planet. As a result, there is a change of day and night. Due to the axial rotation of the Earth, everything moving objects on Earth deviate in the Northern Hemisphere to the right along the course of their movement, in Southern Hemisphere– to the left.
10. What is a year called? How long is one earthly year? Why is every fourth year on Earth longer than the previous three by one day? What are these elongated years called?
A year is the period of time during which the Earth makes full turn around the Sun in its orbit. The Earth year is 365 days. Every fourth year is one day longer than the previous three and is called a leap year. The fact is that the length of an earthly day is just over 24 hours. So in a year you accumulate an extra 6 hours. For convenience, a year is considered to be equal to 365 days. And every four years, add one more day.
11. What is a geographic pole, equator? What is the length of the Earth's equator?
The geographic pole is a conventional point on earth's surface, in which it intersects with the earth's axis.
The equator is an imaginary circle on the surface of the Earth drawn on equal distance from the North and South Pole.
The length of the equator is 40076 km.
12. Why is the distance from the center of the Earth to geographic poles less than from the center of the Earth to the equator?
The polar radius is smaller than the equatorial radius because the Earth is not a perfect sphere, but is slightly flattened at the poles.
13. Why do seasons change on Earth?
The Earth not only rotates around the Sun, but also maintains the tilt of its axis. This leads to uneven heating of different areas over the course of the year, which causes the change of seasons.
14. What are the geographical consequences of the Earth's rotation around the Sun?
The consequence of the movement of the Earth around the Sun is the change of seasons, the annual rhythms of living and inanimate nature.
Materials » An idea of the criterion for the truth of knowledge » What is the orbit of a planet? Can planets collide as they move around the Sun? What is the essence of Kepler's laws? At what average distance from the Sun is the planet Mercury if its period
Planetary orbits are the paths in space along which the planets revolve around the Sun; their shapes are close to circular and their planes are close to the ecliptic plane, with the exception of low-mass bodies (Mercury, Pluto, asteroids). Since each planet has its own path, i.e. their orbit, then they cannot collide.
Each planet moves in its orbit in such a way that its radius vector describes in equal time intervals equal areas. This means that what closer planet towards the Sun, the greater the orbital speed. The ratio of the cubes of the semimajor axes of the orbits of two planets in the Solar System is equal to the ratio of the squares of their periods of revolution around the Sun. The semimajor axis is half the maximum distance between two points on the ellipse. This law made it possible to estimate the size of the solar system.
If Mercury's revolution is equal to 0.24 Earth years, then the distance from the planet to the Sun is approximately equal to ¼ of the distance to Earth.
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ORBIT in astronomy is the path of a celestial body in space. Although an orbit can be called the trajectory of any body, we usually mean the relative motion of interacting bodies: for example, the orbits of planets around the Sun, satellites around a planet, or stars in a complex star system relatively general center wt. An artificial satellite “enters orbit” when it begins to move in a cyclic path around the Earth or the Sun. The term "orbit" is also used in atomic physics when describing electronic configurations.
Absolute and relative orbits
An absolute orbit is the path of a body in a reference system, which in some sense can be considered universal and therefore absolute. The Universe on a large scale, taken as a whole, is considered such a system and is called an “inertial system.” A relative orbit is the path of a body in a reference frame that itself moves along absolute orbit(along a curved path with variable speed). For example, the orbit of an artificial satellite is usually specified by size, shape and orientation relative to the Earth. To a first approximation, this is an ellipse, the focus of which is the Earth, and the plane is motionless relative to the stars. Obviously, this is a relative orbit, since it is defined in relation to the Earth, which itself moves around the Sun. A distant observer will say that the satellite is moving relative to the stars along a complex helical trajectory; this is its absolute orbit. It is clear that the shape of the orbit depends on the motion of the observer's frame of reference.
The need to distinguish between absolute and relative orbits arises because Newton's laws are only valid in an inertial frame, so they can only be used for absolute orbits. However, we always deal with relative orbits celestial bodies, for we observe their movement from the Earth revolving around the Sun and rotating. But if the absolute orbit of an earthly observer is known, then one can either convert all relative orbits into absolute ones, or represent Newton’s laws by equations that are valid in the Earth’s reference frame.
Absolute and relative orbits can be illustrated with an example double star. For example, Sirius, which appears to be a single star to the naked eye, turns out to be a pair of stars when observed with a large telescope. The path of each of them can be traced separately in relation to neighboring stars (taking into account that they themselves are moving). Observations have shown that two stars not only revolve around each other, but also move in space so that between them there is always a point moving in a straight line with constant speed(Fig. 1). This point is called the center of mass of the system. Almost related to her inertial system reference, and the trajectories of stars relative to it represent their absolute orbits. The farther a star moves from the center of mass, the lighter it is. Knowing the absolute orbits allowed astronomers to calculate the masses of Sirius A and Sirius B separately.
If we measure the position of Sirius B relative to Sirius A, we obtain a relative orbit. The distance between these two stars is always equal to the sum of their distances from the center of mass, so the relative orbit has the same shape as the absolute ones, and is equal in size to their sum. Knowing the size of the relative orbit and the period of revolution, it is possible, using Kepler's third law, to calculate only the total mass of stars.
Celestial mechanics
More complex example represents the movement of the Earth, Moon and Sun. Each of these bodies moves in its own absolute orbit relative to a common center of mass. But since the Sun significantly exceeds everyone in mass, it is customary to depict the Moon and Earth as a pair, the center of mass of which moves in a relative elliptical orbit around the Sun. However, this relative orbit is very close to the absolute one.
The motion of the Earth relative to the center of mass of the Earth-Moon system is most accurately measured using radio telescopes, which determine the distance to interplanetary stations. In 1971, during the flight of the Mariner 9 apparatus to Mars, the amplitude of the Earth’s motion was determined from periodic variations in the distance to it with an accuracy of 20–30 m. The center of mass of the Earth–Moon system lies inside the Earth, 1700 km below its surface, and the ratio of the Earth’s masses and the Moon is 81.3007. Knowing their total mass, found from the parameters of the relative orbit, one can easily find the mass of each of the bodies.
Talking about relative motion, we can arbitrarily choose a reference point: the relative orbit of the Earth around the Sun is exactly the same as the relative orbit of the Sun around the Earth. The projection of this orbit onto celestial sphere called the "ecliptic". Over the course of a year, the Sun moves along the ecliptic by approximately 1° per day, and when viewed from the Sun, the Earth moves in the same way. The plane of the ecliptic is inclined to the plane of the celestial equator by 23°27", that is, this is the angle between the earth's equator and its orbital plane. All orbits in the Solar System point relative to the plane of the ecliptic.
Orbits of the Moon and planets
Using the example of the Moon, we will show how the orbit is described. This is a relative orbit, the plane of which is inclined approximately 5° to the ecliptic. This angle is called "inclination" lunar orbit. The plane of the lunar orbit intersects the ecliptic along the “line of nodes.” The one where the Moon passes from south to north is called the “ascending node,” and the other is called the “descending node.”
If the Earth and Moon were isolated from gravitational influence other bodies, the nodes of the lunar orbit would always have a constant position in the sky. But due to the influence of the Sun on the movement of the Moon, reverse movement nodes, i.e. they move west along the ecliptic, completing a full revolution in 18.6 years. Similarly, the orbital nodes artificial satellites move due to the disturbing influence of the equatorial bulge of the Earth.
The Earth is not located in the center of the lunar orbit, but at one of its foci. Therefore, at some point in the orbit the Moon is closest to the Earth; this is "perigee". IN opposite point it is the furthest from Earth; this is the "apogee". (The corresponding terms for the Sun are “perihelion” and “aphelion.”) Half the sum of the distances at perigee and apogee is called the mean distance; it is equal to half largest diameter(major axis) of the orbit, which is why it is called the "semimajor axis". Perigee and apogee are called “apse”, and the line connecting them - the major axis - is called the “apse line”. If it were not for disturbances from the Sun and planets, the line of apses would have a fixed direction in space. But due to disturbances, the line of apses of the lunar orbit moves east with a period of 8.85 years. The same thing happens with the lines of apses of artificial satellites under the influence of the equatorial swelling of the Earth. Planets have apsidal lines (between perihelion and aphelion) moving forward under the influence of other planets.
Conic sections
The size of the orbit is determined by the length of the semimajor axis, and its shape by a quantity called “eccentricity.” The eccentricity of the lunar orbit is calculated by the formula:
(Apogee Distance - Average Distance) / Average Distance
or by formula
(Average distance – Distance at perigee) / Average distance
For planets, apogee and perigee in these formulas are replaced by aphelion and perihelion. Circular orbit eccentricity equal to zero; for all elliptical orbits it is less than 1.0; for a parabolic orbit it is exactly 1.0; for hyperbolic orbits it is greater than 1.0.
An orbit is fully defined if its size (average distance), shape (eccentricity), inclination, position are specified upstream node and the position of perigee (for the Moon) or perihelion (for planets). These quantities are called the “elements” of the orbit. The orbital elements of an artificial satellite are specified in the same way as for the Moon, but usually in relation not to the ecliptic, but to the plane of the earth's equator.
The Moon revolves around the Earth in a time called the “sidereal period” (27.32 days); after it expires, it returns to its original place relative to the stars; this is its true orbital period. But during this time the Sun moves along the ecliptic, and the Moon needs two more days to be in the initial phase, i.e. in the same position relative to the Sun. This period of time is called the “synodic period” of the Moon (approx. 29.5 days). Likewise, the planets revolve around the Sun during the sidereal period, and pass full cycle configurations – from “evening star” to “ morning star"and back - for the synodic period. Some elements of the planets' orbits are indicated in the table.
Orbital speed
The average distance of a satellite from the main component is determined by its speed at some fixed distance. For example, the Earth revolves in an almost circular orbit at a distance of 1 AU. ( astronomical unit) from the Sun at a speed of 29.8 km/s; any other body that has the same speed at the same distance will also move in an orbit with an average distance from the Sun of 1 AU, regardless of the shape of this orbit and the direction of movement along it. Thus, for a body in given point the size of the orbit depends on the value of the speed, and its shape depends on the direction of the speed (see figure).
This has a direct bearing on the orbits of artificial satellites. To put a satellite into a given orbit, it is necessary to deliver it to a certain height above the Earth and give it a certain speed in a certain direction. Moreover, this must be done with high accuracy. If it is required, for example, that the orbit passes at an altitude of 320 km and does not deviate from it by more than 30 km, then at an altitude of 310–330 km its speed should not differ from the calculated one (7.72 km/s) by more than 5 m /s, and the direction of speed should be parallel to the earth’s surface with an accuracy of 0.08°
The above also applies to comets. They usually move in very elongated orbits, the eccentricities of which often reach 0.99. And although their average distances and orbital periods are very long, at perihelion they can approach major planets, for example to Jupiter. Depending on the direction from which the comet approaches Jupiter, its gravity can increase or decrease its speed (see figure). If the speed decreases, the comet will move into a smaller orbit; in this case it is said to be "captured" by the planet. All comets with periods less than a few million years were probably captured in this way.
If the speed of the comet relative to the Sun increases, then its orbit will increase. Moreover, as the speed approaches a certain limit, the growth of the orbit rapidly accelerates. At a distance of 1 AU from the Sun, this maximum speed is 42 km/s. The body moves at a higher speed along a hyperbolic orbit and never returns to perihelion. Therefore, this maximum speed is called “escape speed” with earth's orbit. Closer to the Sun the escape velocity is higher, and farther from the Sun it is lower.
If a comet approaches Jupiter from a great distance, its speed is close to its escape speed. Therefore, flying near Jupiter, the comet only needs to increase its speed slightly to exceed the limit and never return to the vicinity of the Sun. Such comets are called "ejected".
Escape velocity from the Earth
The concept of escape velocity is very important. By the way, it is often also called the “escape” or “escape” speed, and also “parabolic” or “second cosmic velocity”. The last term is used in astronautics when we're talking about about launches to other planets. As already mentioned, for a satellite to move in a low circular orbit, it needs to be given a speed of about 8 km/s, which is called the “first cosmic speed”. (More precisely, if the atmosphere did not interfere, it would be equal to 7.9 km/s at the Earth’s surface.) As the satellite’s speed at the Earth’s surface increases, its orbit becomes more and more elongated: its average distance increases. When the escape velocity is reached, the device will leave the Earth forever.
Calculating this critical speed is quite simple. Near Earth kinetic energy body must be equal to the work done by gravity when moving a body from the surface of the Earth “to infinity”. Since attraction decreases rapidly with height (inversely proportional to the square of the distance), we can limit ourselves to working at a distance of the radius of the Earth:
Here on the left is the kinetic energy of a body of mass moving with speed, and on the right is the work of gravity mg at a distance of the radius of the Earth (R = 6371 km). From this equation we find the speed (and this is not an approximate, but an exact expression):
Because acceleration free fall at the Earth's surface is g = 9.8 m/s2, the escape velocity will be equal to 11.2 km/s.
Orbit of the Sun
The Sun itself, together with the surrounding planets and small bodies of the Solar System, moves in its galactic orbit. Towards to the nearest stars The sun flies at a speed of 19 km/s towards a point in the constellation Hercules. This point is called the "apex" solar movement. In general, the entire group of nearby stars, including the Sun, revolves around the center of the Galaxy in an orbit with a radius of 251016 km at a speed of 220 km/s and a period of 230 million years. This orbit is quite complex because the Sun's motion is constantly being disturbed by other stars and massive clouds of interstellar gas.
Bibliography
To prepare this work, materials from the site http://www.astro-azbuka.info were used
What is "Orbit"? How to spell given word. Concept and interpretation.
Orbit in astronomy, the path of a celestial body in space. Although an orbit can be called the trajectory of any body, it usually refers to the relative motion of interacting bodies: for example, the orbits of planets around the Sun, satellites around a planet, or stars in a complex star system relative to a common center of mass. An artificial satellite “enters orbit” when it begins to move in a cyclic path around the Earth or the Sun. The term "orbit" is also used in atomic physics to describe electron configurations. See also ATOM. Absolute and relative orbits. An absolute orbit is the path of a body in a reference system, which in some sense can be considered universal and therefore absolute. The Universe on a large scale, taken as a whole, is considered such a system and is called an “inertial system.” A relative orbit is the path of a body in a reference system that itself moves along an absolute orbit (along a curved path with variable speed). For example, the orbit of an artificial satellite is usually specified by size, shape and orientation relative to the Earth. To a first approximation, this is an ellipse, the focus of which is the Earth, and the plane is motionless relative to the stars. Obviously, this is a relative orbit, since it is defined in relation to the Earth, which itself moves around the Sun. A distant observer will say that the satellite is moving relative to the stars along a complex helical trajectory; this is its absolute orbit. It is clear that the shape of the orbit depends on the motion of the observer's frame of reference. The need to distinguish between absolute and relative orbits arises because Newton's laws are only valid in an inertial frame, so they can only be used for absolute orbits. However, we always deal with the relative orbits of celestial bodies, because we observe their movement from the Earth revolving around the Sun and rotating. But if the absolute orbit of an earthly observer is known, then one can either convert all relative orbits into absolute ones, or represent Newton’s laws by equations that are valid in the Earth’s reference frame. Absolute and relative orbits can be illustrated using the example of a binary star. For example, Sirius, which appears to be a single star to the naked eye, turns out to be a pair of stars when observed with a large telescope. The path of each of them can be traced separately in relation to neighboring stars (taking into account that they themselves are moving). Observations have shown that two stars not only revolve around each other, but also move in space so that between them there is always a point moving in a straight line with a constant speed (Fig. 1). This point is called the center of mass of the system. In practice, an inertial reference frame is associated with it, and the trajectories of stars relative to it represent their absolute orbits. The farther a star moves from the center of mass, the lighter it is. Knowing the absolute orbits allowed astronomers to separately calculate the masses of Sirius A and Sirius B. Fig. 1. ABSOLUTE ORBIT of Sirius A and Sirius B according to observations over 100 years. The center of mass of this binary star is moving in a straight line in an inertial frame; therefore, the trajectories of both stars in this system are their absolute orbits.
Orbit- ORBIT w. lat. astr. the planet's circular path around the sun; cru" ovina. doctor. eye orbit, cavity... Dahl's Explanatory Dictionary
Orbit- ORBIT, orbits, w. (Latin orbita, lit. wheel trace) (book). 1. The path of movement of a celestial body (ast... Ushakov’s Explanatory Dictionary
Orbit- and. 1. The path along which a celestial body moves under the influence of the attraction of other celestial bodies. // Put... Efremova's Explanatory Dictionary
Orbit- ORBIT (from the Latin orbita - track, path), 1) the path along which one celestial body (planet, its back...
ORBIT in astronomy is the path of a celestial body in space. Although an orbit can be called the trajectory of any body, it usually refers to the relative motion of interacting bodies: for example, the orbits of planets around the Sun, satellites around a planet, or stars in a complex star system relative to a common center of mass. An artificial satellite “enters orbit” when it begins to move in a cyclic path around the Earth or the Sun. The term "orbit" is also used in atomic physics to describe electron configurations.
Absolute and relative orbits
An absolute orbit is the path of a body in a reference system, which in some sense can be considered universal and therefore absolute. The Universe on a large scale, taken as a whole, is considered such a system and is called an “inertial system.” A relative orbit is the path of a body in a reference system that itself moves along an absolute orbit (along a curved path with variable speed). For example, the orbit of an artificial satellite is usually specified by size, shape and orientation relative to the Earth. To a first approximation, this is an ellipse, the focus of which is the Earth, and the plane is motionless relative to the stars. Obviously, this is a relative orbit, since it is defined in relation to the Earth, which itself moves around the Sun. A distant observer will say that the satellite is moving relative to the stars along a complex helical trajectory; this is its absolute orbit. It is clear that the shape of the orbit depends on the motion of the observer's frame of reference.
The need to distinguish between absolute and relative orbits arises because Newton's laws are only valid in an inertial frame, so they can only be used for absolute orbits. However, we always deal with the relative orbits of celestial bodies, because we observe their movement from the Earth revolving around the Sun and rotating. But if the absolute orbit of an earthly observer is known, then one can either convert all relative orbits into absolute ones, or represent Newton’s laws by equations that are valid in the Earth’s reference frame.
Absolute and relative orbits can be illustrated using the example of a binary star. For example, Sirius, which appears to be a single star to the naked eye, turns out to be a pair of stars when observed with a large telescope. The path of each of them can be traced separately in relation to neighboring stars (taking into account that they themselves are moving). Observations have shown that two stars not only revolve around each other, but also move in space so that between them there is always a point moving in a straight line with a constant speed (Fig. 1). This point is called the center of mass of the system. In practice, an inertial reference frame is associated with it, and the trajectories of stars relative to it represent their absolute orbits. The farther a star moves from the center of mass, the lighter it is. Knowing the absolute orbits allowed astronomers to calculate the masses of Sirius A and Sirius B separately.
If we measure the position of Sirius B relative to Sirius A, we obtain a relative orbit. The distance between these two stars is always equal to the sum of their distances from the center of mass, so the relative orbit has the same shape as the absolute ones, and is equal in size to their sum. Knowing the size of the relative orbit and the period of revolution, it is possible, using Kepler's third law, to calculate only the total mass of stars.
Celestial mechanics
A more complex example is the movement of the Earth, Moon and Sun. Each of these bodies moves in its own absolute orbit relative to a common center of mass. But since the Sun significantly exceeds everyone in mass, it is customary to depict the Moon and Earth as a pair, the center of mass of which moves in a relative elliptical orbit around the Sun. However, this relative orbit is very close to the absolute one.
The motion of the Earth relative to the center of mass of the Earth-Moon system is most accurately measured using radio telescopes, which determine the distance to interplanetary stations. In 1971, during the flight of the Mariner 9 apparatus to Mars, the amplitude of the Earth’s motion was determined from periodic variations in the distance to it with an accuracy of 20–30 m. The center of mass of the Earth–Moon system lies inside the Earth, 1700 km below its surface, and the ratio of the Earth’s masses and the Moon is 81.3007. Knowing their total mass, found from the parameters of the relative orbit, one can easily find the mass of each of the bodies.
When talking about relative motion, we can arbitrarily choose a reference point: the relative orbit of the Earth around the Sun is exactly the same as the relative orbit of the Sun around the Earth. The projection of this orbit onto the celestial sphere is called the “ecliptic.” Over the course of a year, the Sun moves along the ecliptic by approximately 1° per day, and when viewed from the Sun, the Earth moves in the same way. The plane of the ecliptic is inclined to the plane of the celestial equator by 23°27", that is, this is the angle between the earth's equator and its orbital plane. All orbits in the Solar System point relative to the plane of the ecliptic.
Orbits of the Moon and planets
Using the example of the Moon, we will show how the orbit is described. This is a relative orbit, the plane of which is inclined approximately 5° to the ecliptic. This angle is called the "inclination" of the lunar orbit. The plane of the lunar orbit intersects the ecliptic along the “line of nodes.” The one where the Moon passes from south to north is called the “ascending node,” and the other is called the “descending node.”
If the Earth and Moon were isolated from the gravitational influence of other bodies, the nodes of the lunar orbit would always have a constant position in the sky. But due to the influence of the Sun on the movement of the Moon, the reverse movement of the nodes occurs, i.e. they move west along the ecliptic, completing a full revolution in 18.6 years. Similarly, the orbital nodes of artificial satellites move due to the disturbing influence of the Earth's equatorial bulge.
The Earth is not located in the center of the lunar orbit, but at one of its foci. Therefore, at some point in the orbit the Moon is closest to the Earth; this is "perigee". At the opposite point it is furthest from Earth; this is the "apogee". (The corresponding terms for the Sun are “perihelion” and “aphelion.”) Half the sum of the distances at perigee and apogee is called the mean distance; it is equal to half the largest diameter (major axis) of the orbit, which is why it is called the “semimajor axis.” Perigee and apogee are called “apse”, and the line connecting them - the major axis - is called the “apse line”. If it were not for disturbances from the Sun and planets, the line of apses would have a fixed direction in space. But due to disturbances, the line of apses of the lunar orbit moves east with a period of 8.85 years. The same thing happens with the lines of apses of artificial satellites under the influence of the equatorial swelling of the Earth. Planets have apsidal lines (between perihelion and aphelion) moving forward under the influence of other planets.
Conic sections
The size of the orbit is determined by the length of the semimajor axis, and its shape by a quantity called “eccentricity.” The eccentricity of the lunar orbit is calculated by the formula:
(Apogee Distance - Average Distance) / Average Distance
or by formula
(Average distance – Distance at perigee) / Average distance
For planets, apogee and perigee in these formulas are replaced by aphelion and perihelion. The eccentricity of a circular orbit is zero; for all elliptical orbits it is less than 1.0; for a parabolic orbit it is exactly 1.0; for hyperbolic orbits it is greater than 1.0.
An orbit is fully defined when its size (average distance), shape (eccentricity), inclination, position of the ascending node, and position of perigee (for the Moon) or perihelion (for planets) are specified. These quantities are called the “elements” of the orbit. The orbital elements of an artificial satellite are specified in the same way as for the Moon, but usually in relation not to the ecliptic, but to the plane of the earth's equator.
The Moon revolves around the Earth in a time called the “sidereal period” (27.32 days); after it expires, it returns to its original place relative to the stars; this is its true orbital period. But during this time the Sun moves along the ecliptic, and the Moon needs two more days to be in the initial phase, i.e. in the same position relative to the Sun. This period of time is called the “synodic period” of the Moon (approx. 29.5 days). In the same way, the planets revolve around the Sun during the sidereal period, and go through a full cycle of configurations - from the “evening star” to the “morning star” and back - during the synodic period. Some elements of the planets' orbits are indicated in the table.
Orbital speed
The average distance of a satellite from the main component is determined by its speed at some fixed distance. For example, the Earth revolves in an almost circular orbit at a distance of 1 AU. (astronomical unit) from the Sun at a speed of 29.8 km/s; any other body that has the same speed at the same distance will also move in an orbit with an average distance from the Sun of 1 AU, regardless of the shape of this orbit and the direction of movement along it. Thus, for a body at a given point, the size of the orbit depends on the value of the velocity, and its shape depends on the direction of the velocity (see figure).
This has a direct bearing on the orbits of artificial satellites. To put a satellite into a given orbit, it is necessary to deliver it to a certain height above the Earth and give it a certain speed in a certain direction. Moreover, this must be done with high precision. If it is required, for example, that the orbit passes at an altitude of 320 km and does not deviate from it by more than 30 km, then at an altitude of 310–330 km its speed should not differ from the calculated one (7.72 km/s) by more than 5 m /s, and the direction of speed should be parallel to the earth’s surface with an accuracy of 0.08°
The above also applies to comets. They usually move in very elongated orbits, the eccentricities of which often reach 0.99. And although their average distances and orbital periods are very long, at perihelion they can approach large planets, such as Jupiter. Depending on the direction from which the comet approaches Jupiter, its gravity can increase or decrease its speed (see figure). If the speed decreases, the comet will move into a smaller orbit; in this case it is said to be "captured" by the planet. All comets with periods less than a few million years were probably captured in this way.