Over the centuries, astronomers have learned about the structure of the solar system and its many planets and moons. These discoveries have opened new vistas of planetary exploration.
Over the last decade, NASA has been expanding its human space program and pursuing joint robotic missions to Mars and near-Earth asteroids. This has increased the importance of a well-funded exploration program for our nation and the world.
Astronomy is the study of celestial objects – including planets, stars, comets and galaxies – and phenomena that originate outside Earth’s atmosphere. It focuses on the origin, evolution and current state of these varied objects in our universe as well as their interactions with each other.
Astronomers also investigate a variety of other issues, such as the search for extraterrestrial life. This includes astrochemistry, which looks at how substances in space can affect our planet and how life might develop on other worlds. In addition, astronomy scientists use astrophysics to learn about the formation of stars and galaxy clusters.
For ancient cultures, astronomy was an important part of their lives, especially as it allowed them to predict seasons and navigate over large distances. Astronomy also allowed them to form calendars that helped them track events throughout the year.
Early astronomers also studied the stars in our galaxy, developing a wide range of names that are still used today. They were also able to calculate the positions of the Sun and Moon, which became an essential tool for farmers who needed to know when to sow seeds or harvest crops.
In terms of observing objects, most astronomical research is done with optical instruments, such as telescopes and spectrographs. These tools use mirrors, lenses and cameras to observe light wavelengths that range from near infrared to visible (about 400 – 700 nm). High-energy astronomy, on the other hand, uses more sensitive instruments that look for X-rays, gamma rays and extreme UV light.
The observable universe is vast and ancient, full of ever-astounding phenomena. As a result, astronomy has been one of the most popular sciences for students throughout history.
There are several subfields in astronomy, with some of them related directly to space exploration, such as instrumentation and planetary sciences. Others, such as cosmology and data science, are more theoretical.
Astronomy has a long history, with its roots reaching back to the Babylonian era. Ancient Greeks elevated sky-watching to a new level, using mathematical methods to estimate the sizes and motions of the planets and stars. These methods were also used by many other cultures across the globe, and have since led to some of the most important discoveries in astronomy.
Spacecraft are vehicles that travel in the solar system and beyond, outside of Earth’s atmosphere. They are used for a variety of purposes, including communications, meteorology, navigation, and space exploration.
A spacecraft usually consists of several subsystems, depending on its mission profile. These include: attitude determination and control (variously referred to as ADAC, ADC or ACS); guidance, navigation and control; communications; command and data handling; power; thermal control; structures; and payloads.
Attitude control is the process of adjusting a spacecraft’s position and direction to achieve the desired flight path, often using specialized sensors. It can be done through radio signals or computer software commands sent from Earth.
The Sun, planets and moons are constantly moving, so scientists must predict where a spacecraft will be and how fast it will move in order to reach its destination. They also need to consider gravity, which can bend a spacecraft’s path and force it to swing by or be pulled into orbit by a planet or moon.
Many spacecraft are ‘three-axis stabilised’, meaning that they have their attitude determined by an axes that point at the Sun or other stars. Planck, for example, revolves about a Sun-pointing axis once every minute to stabilise its orientation.
For most interplanetary spacecraft, the trajectory is set before launch. From there, the spacecraft uses small engines or thrusters to correct its trajectory until it reaches its destination.
There are many types of propulsion systems for interplanetary spacecraft, from traditional chemical rockets to ion drives and nuclear engines. The simplest type of propulsion system is called ‘cold gas’, which involves pressing a stream of pressurized gas through a nozzle.
Other systems may include reaction or momentum wheels to control the spacecraft’s attitude. These are controlled by a series of computer algorithms that take into account the spacecraft’s position, orientation and velocity.
In addition, spacecraft may have a communication system that allows them to send messages back and forth with ground stations on Earth. These can be made of a variety of technologies, such as RF and optical transmissions.
A spacecraft also has a life support system, which can include oxygen systems and other equipment to supply the crew with air, food, water, and other materials needed to live in space. These can be expensive to build and launch, but they are important for a variety of reasons, including:
The solar system contains eight planets and numerous other objects, including satellites, planetary rings, comets, asteroids, meteoroids, and moons. Scientists are interested in the composition and evolution of these bodies, as well as what makes them habitable or unhabitable.
Astronomers have a wide range of tools for studying the solar system, including spacecraft and telescopes. They use these instruments to determine the composition of the planets and their atmospheres, and to study their magnetic fields and tectonics. They also use these instruments to make more accurate predictions about the sun’s impact on Earth and other planets.
Most of the planets in our Solar System are gas giants, consisting of hydrogen and helium. They were formed when the earliest stars began to shed material, leaving behind a disk of gas and debris. The gas in this disk was drawn into the solar system by the Sun’s gravity.
These gases cooled into solids, and eventually became planets. The four gas giants – Jupiter, Saturn, Uranus, and Neptune – are about 11 times the size of the Earth; they are almost as large as a star.
Besides the gas giants, there are a number of smaller planets called dwarf planets. Some of these dwarf planets are rocky, while others are made of ice.
A large number of these smaller planets are found in a belt around the Sun, called the asteroid belt. The asteroid belt is filled with millions of asteroids; some of these asteroids are small enough to be seen with the naked eye.
Many of the asteroids and minor planets that are located in our asteroid belt and around the Sun have orbits very close to the Earth’s. These orbits are called perihelions and aphelions, respectively. The perihelions are closest to the Sun, while the aphelions are farthest away.
The asteroid belt is also home to many comets, most of which are very short-period. These comets are not visible to the naked eye, but they can be detected using radio signals from spacecraft or other instruments in the astronomical community.
The International Astronomical Union (IAU) uses the geophysical definition of a planet to classify a body as a planet when it satisfies three criteria. The first is that it must be in orbit around the Sun; the second is that it must have sufficient mass for its self-gravity to overcome its rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape; and the third is that it must have “cleared its neighborhood” of most other orbiting bodies. Because Pluto has not met all of these criteria, it was reclassified as a dwarf planet in 2006.
The Moon is one of the most important bodies in the solar system. Not only does it orbit around Earth, but it is also the only extraterrestrial body that has ever been visited by humans. Its gravity helps stabilize the axis of rotation for our planet, and its orbital motion also causes rises and falls in sea levels called tides.
Scientists have been studying the moon for decades, learning more about its origin and geologic history. Its craters preserve evidence of past impacts by asteroids and comets.
These impacts, which occurred about 4 billion years ago, blasted rocks from the early Earth and other parts of our solar system into space. They formed a series of huge basins, which later became filled in with dark rock.
During this time, the Moon also experienced intense bombardment by asteroids and comets. These impacts, which happened in waves or a single massive storm, have shaped the surface of the Moon and its craters to a great extent.
For this reason, the Moon is a critical research target for many human spaceflight programs. It is an ideal environment to study how space radiation and micrometeorite bombardment can affect astronauts in space, particularly if they are living on a long-term basis, as is the case for future missions to Mars.
It is also a valuable research tool for understanding the effects of planetary climate change on Earth. The Moon’s libration, or apparent spinning motion, creates variations in sunlight and temperature. The resulting shifts in brightness and temperature can cause changes in local weather patterns, which are critical for the survival of animals such as the California grunion fish and several types of sea turtles.
Finally, the moon is a key source of information about our solar system’s formation and evolution. It has been analyzed for its chemical composition, topography, magnetic fields and other characteristics.
Since 2009, NASA’s Lunar Reconnaissance Orbiter has been orbiting the Moon to scout the surface for potential landing sites. It has also detected water ice on the Moon’s poles, which could help fuel the development of future lunar habitats.