Class Notes Objects in the Universe Major components

Class Notes: Objects in the Universe Major components of the universe include Galaxies Black Holes Nebulae Stars A galaxy is a large grouping of stars and interstellar gas and dust. These components are held together in the galaxy by their gravity. A black hole is a dense body thought to have zero volume but infinite density, which forms an intense gravity well in space A nebula is a hot cloud of gas and dust. Stars are formed in the nebula as its materials slowly condense into regions of higher density due to gravity. a star is a large ball of gas or plasma that is held together by its own gravity.

Universe, Galaxy, Solar System

How do we define the term “universe” ? Universe: commonly defined as the totality of existence, including planets, stars, galaxies, the contents of intergalactic space (areas between galaxies), and all matter and energy

Galaxies: massive, gravitationally bound systems consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter

Solar System Solar System: The Sun together with the group of planets and other celestial bodies that are held by its gravitational attraction and revolve around it

There is a wide range of galaxy shapes and sizes. There are four classifications of galaxies, based on their shapes: elliptical spiral lenticular (lens-shaped) irregular. Our galaxy, the Milky Way, is a spiral galaxy.

Astronomical bodies Planets Stars Moons Asteroids Nebulae Galaxies Dwarf planets Comets

Distance There are enormous distances between objects in space. We use the idea of light years and scientific notation to help us grasp these large distances A light-year-How far a beam of light travels in one year In one year light travels 9. 4607 × 1012 km Or you can think about it in miles 6 trillion miles

Stars radiate energy through the process of fusion in which two hydrogen atoms are combined to form a helium atom, and large amounts of energy are released. Some of the energy generated by the star is in the form of visible light.

Stars The size and composition of a star determine the amount of gravity (more mass generates more gravity) and energy it emits. Scientists use the Hertzsprung-Russell diagram to understand the relationship between a star’s brightness and its surface temperature.

Where are most of the stars? On the Hertzsprung-Russell diagram there is a band known as the main sequence which contains about 90% of all stars. This shows that there is a strong relationship between a star’s brightness and its surface temperature. The other 10% of stars are special types (supergiants, and white dwarfs), and each group falls in a specific area on the diagram.

Hertzsprung-Russell diagram A B S O L U T E Scientists use the Hertzsprung-Russell diagram to understand the relationship between a star’s brightness and its surface temperature.

The physical properties of stars: Apparent Magnitude (brightness) Ø gives the brightness of an object, observed from any point. Absolute brightness (Luminosity) Ø gives the brightness of an object as seen from 10 parsecs away. Temperature Ø color Size

Apparent magnitude gives the brightness of an object, observed from any point. Absolute magnitude gives the brightness of an object as seen from 10 parsecs away.

Brightness The closer and object is to earth the brighter it looks to the human eye. Closer=brighter More distant=fainter in its brightness

Absolute Magnitude The absolute magnitude of an object is defined as the brightness of an object at a distance of 10 parsecs away from it. (A parsec is a unit used to measuring distances between stars. A parsec is about 3. 26 light years, and the distance between the Sun and Proxima Centauri, the closest star to the Sun is about 1. 3 parsecs).

How do I actually Use this?

The law of Universal Gravitation Key concepts: Gravity is a force of attraction between two or more masses. The Sun, as the most massive object in our solar system, determines the motion of all other bodies in the system by the force of gravity. Bodies of the solar system remain in their orbital paths due to a balance between gravitational forces and the constant forward motion of the celestial bodies. Strength of the gravitational attraction depends on the mass of the objects involved and on the distance between them. Gravitational attraction exhibited by an object increases with increasing mass. If the distance between objects increases, gravitational attraction between the objects decreases.

Spectrograph-Scientists uses these to determine the elements found in stars. It breaks light into colors and produces an image of the resulting spectrum

Background Info All of the celestial bodies in the solar system move in predictable patterns known as orbits, and this motion is controlled by gravity. Every celestial body (including Earth) is surrounded by its own gravitational field, which exerts an attractive force on all objects. The Sun’s massive gravitational field causes the entire solar system to orbit around it. Earth’s gravitational field attracts the Moon and holds it in orbit. The Moon’s gravitational field has attracted numerous meteorites that made impact craters, and so on.

Gravity in Space- MASS and DISTANCE Everything that has mass has gravity. The more mass an object has, the stronger its gravitational pull on other objects. For example, Earth has more mass than the Moon, so its gravitational field is stronger. As the distance between two masses increases, the gravitational attraction between them decreases So gravity depends directly on the mass of the objects and inversely on how far apart they are:

What would happen if there was no gravity in space? Earth’s orbit around the Sun is determined by the balance of the Sun’s gravitational pull on Earth and Earth’s forward momentum as it travels around the Sun. Without the Sun’s gravitational pull, Earth would not move in a circle around the Sun, but would continue moving in a straight line through the Milky Way. Without Earth’s momentum, the Sun would pull Earth into itself. If an object does not have enough orbital speed or momentum to resist the pull of gravity, then it will be pulled into the surface of the larger object. That is why meteorites crash into the surface of moons and planets. That is also why the Moon does not crash into Earth; it is orbiting at just the right speed and has just the right forward momentum to stay in orbit around Earth.

Planets that orbit the sun The Planets Eight major planets orbit the Sun. They fall into two main categories: Inner Planets Outer Planets

Inner Planets The inner planets: Mercury, Venus, Earth, and Mars. “terrestrial” (“like Earth”) rocky planets small and have a dense, solid core and surface, which we could stand on

Outer Planets The outer planets Jupiter, Saturn, Uranus, and Neptune “Jovian” (“like Jupiter”) planets or gas giants large and have extensive atmospheres. Trying to stand on their visible surfaces would be like trying to stand on a cloud.

Pluto is a special case. It used to be called the ninth planet, but after the discovery of several objects similar to Pluto further out in the Solar System— the largest of which is larger than Pluto—the International Astronomical Union decided in 2006 that Pluto belongs to a new class of objects called dwarf planets, and is not an actual planet. It is small, like the terrestrial planets, but unlike them, is made of a mixture of ice and rock.

Comparing Objects in our Solar System-Review and New Content The Sun is at the center of our solar system, and its strong gravitational pull holds eight planets, asteroids, and other celestial objects in orbital paths around it. Planets in the solar system revolve around the Sun in an orbital path and can be either rocky, terrestrial objects, or large and gaseous. Each planet rotates (spins) on an axis. The inner planets of Mercury, Venus, Earth, and Mars are mostly solid with minerals similar to those on Earth. The outer planets of Jupiter, Saturn, Uranus, and Neptune are gaseous masses with rocky cores surrounded by liquids. Moons are smaller celestial objects that orbit planets.

Sun Is a medium-sized star The most massive object in our solar system It is an extremely hot, dense mass of gases, which radiates visible light and charged particles. Located at the center of our solar system, the Sun rotates (spins) on its axis and does not have a solid surface. Planets in the solar system revolve around the Sun in an orbital path

Electromagnetic Spectrum The electromagnetic spectrum is a range of all types of electromagnetic radiation ranging from very short wavelengths, including gamma and x-rays, to very long wavelengths, including microwaves and radio waves. Radiation is energy that travels and spreads through space. By studying wavelengths of the electromagnetic spectrum that reach Earth from stars and other bodies in the universe, scientists have been able to analyze properties, distances, and motion of objects in the universe.

Electromagnetic Spectrum All objects in the universe emit electromagnetic radiation. By measuring the wavelengths or frequencies of light coming from objects, scientists can infer some of their physical properties. The amount of radiation emitted at each wavelength indicates the temperature of the object. Therefore, scientists can estimate the temperatures of faraway celestial bodies based on the wavelengths of radiation they emit

Technology Until space travel becomes more commonplace, scientists must depend on electromagnetic radiation to bring them information about distant objects in space. New technologies developed in the late 20 th century and early 21 st century allow scientists to use many regions of the electromagnetic spectrum to explore and measure the universe. Using devices that are sensitive to light that is not detectable by human eyes, scientists can “see” by using computer imageprocessing techniques that assign arbitrary color values to the light.

EM Spectrum

Longest wavelength: Radio Waves Shortest wavelength: Gamma Rays LONGEST----RMIVUXG-----SHORTEST

Visible Light (ROYGBIV) The only region in the electromagnetic spectrum that human eyes can detect is called the visible region. Visible light includes the colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet. Within the visible light region, red light has the longest wavelength and violet light has the shortest.

Jupiter’s diameter is roughly 11 times that of Earth, and 2. 5 the mass of all the other planets in the Solar System combined.

Mercury The smallest planet in regards to both mass and volume is Mercury—this tiny planet is nearly 20 times less massive than Earth, and its diameter is about times 2 ½ smaller. In fact, Mercury is closer in size to our Moon than to Earth.

Grapefruit Peppercorn Large blueberry Pea Watermelon Apple Lime Cherry Tomato

A size comparison of the planets in our solar system. In order of increasing distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.