Astronomy Exam 1 Study Guide Chapters 1-5

How old is our solar system?

4.6 billion years old.

Example of: Total energy staying the same but changing form

A ball dropped from a height is an example of a change of energy from potential to kinetic energy.

What is an ellipse?

A closed plane curve generated by a point moving in a way that the sums of its distances from two fixed points is a constant, oval shape. (The shape of Earth's orbit)

What is a constellation?

A constellation is a group of stars that looks like a particular shape in the sky and has been given a name. These stars are far away from Earth. They are not connected to each other at all.

What is a star?

A fixed luminous point in the night sky which is a large, remote incandescent body like the sun.

What is a group of galaxies? (GRG)

A group consisting of 50 or fewer gravitationally bound members, each must be at least as luminous (or bright) as the Milky Way.

Kepler's Second Law of Motion

A planet moves faster when it is closer to the sun and slower when it is further away. Or, a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

What is a focus?

A point at which rays of light come together or from which they appear to spread apart, as after passing through a lens.

What is force?

A push or a pull.

What is an epicycle?

A small circle whose center moves around the circumference of a larger one.

What are solar and lunar eclipses?

A solar eclipse occurs when the moon passes directly between Earth and the sun, blocking sunlight from Earth. During a lunar eclipse, Earth blocks sunlight from reaching the moon.

What is a galaxy?

A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.

Why isn't the Sun always on the meridian at noon?

All meridians converge at the North Pole and the South Pole. So, unlike any other location on Earth, the poles don't have a longitude. By extension, there is no solar noon because there is no meridian the Sun can cross. In practice, the Sun does not go up and down on a daily basis like everywhere else on Earth.

What are eclipses?

An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer.

Newton's first law of Motion

An object in motion will remain in motion unless acted upon by another force.

How does the force of gravity depend on the two things pulling each other together, and how does it depend on how far apart they are?

Anything that has mass also has gravity. Objects with more mass have more gravity. Gravity also gets weaker with distance. So, the closer objects are to each other, the stronger their gravitational pull is. Earth's gravity comes from all its mass.

What causes the changing length of daylight?

As the Earth moves around the Sun, the length of the day changes. The length of day at a particular location on Earth is a periodic function of time. This is all caused by the 23.5-degree tilt of the Earth's axis as it travels around the sun.

Why aren't there eclipses each month?

Because the Earth's orbit around the sun is not in the same plane as the Moon's orbit around the Earth.

How did the ancient Greeks think that planets moved?

Circular.

What are conservation laws?

Conservation laws state that a particular measurable property of an isolated physical system does not change as the system evolves over time

What was the historical role of Johannes Kepler?

Discovered that the Earth and planets travel about the sun in elliptical orbits. He gave three fundamental laws of planetary motion

What are spectral lines (emission and absorption) and how are they related to energy levels of electrons in atoms?

Emission Lines: Emission lines are usually seen as bright lines, or lines of increased intensity, on a continuous spectrum. Absorption Lines: Absorption lines are usually seen as dark lines, or lines of reduced intensity, on a continuous spectrum. This is seen in the spectra of stars, where gas (mostly hydrogen) in the outer layers of the star absorbs some of the light from the underlying thermal blackbody spectrum.

Newton's Third Law of Motion

For every action there is an equal and opposite reaction.

How do we use spectral lines to learn what things are made of and how they are moving?

From spectral lines astronomers can determine not only the element, but the temperature and density of that element in the star. The spectral line also can tell us about any magnetic field of the star. The width of the line can tell us how fast the material is moving. We can learn about winds in stars from this.

What was the historical role of Galileo?

Galileo's discoveries about the Moon, Jupiter's moons, Venus, and sunspots supported the idea that the Sun - not the Earth - was the center of the Universe, as was commonly believed at the time.

What discoveries did Galileo make using a telescope that showed that the Earth was not at the center?

Galileo's observations of the phases of Venus virtually proved that the Earth was not the center of the universe.

Why are astronauts on the International Space Station weightless?

Gravity is almost as strong at the height of the International Space Station as on the surface of the Earth -- only about 10 percent weaker. It's not the height, but the motion of the spacecraft that causes weightlessness. Any object that is falling freely is weightless, no matter where it happens to be. (Freefall)

What was the historical role of Copernicus?

He was the first modern European scientist to propose that Earth and other planets revolve around the sun, or the Heliocentric Theory of the universe.

Example of: Momentum staying the same but changing among objects

If two objects (a car and a truck, for example) collide, momentum will always be conserved.

How did Ptolemy's model predict Venus went through phases and what did Copernicus's model predict?

In the Ptolemeic model, Venus is always between the earth and the sun, so would only show crescents. Even greatest elongation would not give a half Venus, because the triangle made between the sun, earth and Venus would not be a right triangle. Galileo's studies of motion also led him to discover the basic idea of inertia.

Further from the sun and larger than the other 4 planets

Jupiter, Saturn, Uranus & Neptune.

How is light like a particle?

Light as a Particle Light behaves mainly like a wave but it can also be considered to consist of tiny packages of energy called photons. Photons carry a fixed amount of energy but have no mass.

Which have higher and lower wavelength and frequency and energy: infrared, radio, X-ray, ultraviolet, visible, microwave, gamma rays?

Lowest to Highest Frequencies: Microwaves, infrared, red, ultraviolet, and gamma waves. The energy of an electromagnetic wave is directly proportional to its frequency.

Closer to the sun and smaller than the other 4 planets

Mercury, Venus, Earth & Mars

How did Newton's understanding of gravity help explain orbits better?

Newton went further and proposed that gravity was a "universal" force, and that the Sun's gravity was what held planets in their orbits. He was then able to show that Kepler's laws were a natural consequence of the "inverse squares law"

What is Newton's Law of Universal Gravitation?

Newton's law of gravitation, statement that any particle of matter in the universe attracts any other with a force varying directly as the product of the masses and inversely as the square of the distance between them.

How did Newton advance our understanding of how planets move?

Newton's laws of motion and gravity explained Earth's annual journey around the Sun. Earth would move straight forward through the universe, but the Sun exerts a constant pull on our planet. This force bends Earth's path toward the Sun, pulling the planet into an elliptical (almost circular) orbit.

What is a planet?

Objects within the solar system that orbit the sun. In order of closeness to the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

What is the semimajor axis?

One half the major axis of an ellipse.

What is a period?

Periods in astronomy are conveniently expressed in various units of time, often in hours, days, or years. They can be also defined under different specific astronomical definitions that are mostly caused by the small complex external gravitational influences of other celestial objects.

Kepler's 1st law of motion

Planets travel around the sun in an elliptical orbit. (A closed plane curve generated by a point moving in a way that the sums of its distances from two fixed points is a constant, oval shape)

What is the celestial equator?

Projection of the Earth's equator into space.

What was the historical role of Ptolemy?

Ptolemaic system Ptolemy believed that Earth was at the center of the universe and that the sun and planets orbited Earth (with the planets also moving in smaller circles called epicycles). In this system, the centers of Mercury's and Venus's epicycles always lie on the line shown in the diagram between Earth and the sun.

What is retrograde motion?

Retrograde motion simply describes an object that is moving in the opposite direction in relation to another moving object, and is a term that is commonly used in astronomy to describe the motion of various celestial bodies.

How was retrograde motion explained by having planets orbit the Sun instead of the Earth?

Rotation in the opposite direction of what is expected or most common is called retrograde. Copernicus argued that Earth orbits the Sun like all the other planets, providing a more natural explanation for retrograde motion.

How old do we think the universe is?

Roughly 13.7 billon years old.

What are millions, billions, and trillions written out in scientific notation?

Scientific notation represents numbers in powers of ten. So 60m million would be 6x10 to the 7th power.

What are sidereal and solar time?

Solar time: is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Two types of solar times are apparent solar time (sundial time) and mean solar time (clock time) Sidereal time: Time reckoned from the motion of the earth (or a planet) relative to the distant stars (rather than with respect to the sun).

What causes tides? How are tides related to gravity?

Stronger gravitational pull on the Earth that faces the moon results in a higher tide, if the moon isn't directly facing directly in front of earth then there's a weaker gravitational pull.

What is a solar system?

System of the sun and the objects that orbit it (The 8 planets, asteroids, & dwarf planets).

What is the moon?

The Moon is an astronomical body that orbits planet Earth and is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits (its primary).

Newton's Second Law of Motion

The acceleration of an object depends on the mass of the object and the amount of force applied. Force = Mass x Acceleration

What is mass?

The amount of matter in an object.

What is the electromagnetic spectrum?

The complete range of electromagnetic waves placed in order of increasing frequency.

How does conservation of angular momentum help to explain one of Kepler's Laws?

The conservation of orbital momentum actually explains Kepler's second law of planetary motion. According Kepler's second law of planetary motion, as a planet moves around its orbit, it sweeps out equal areas in equal time. The formula for orbital angular momentum is: angular momentum = m*v*r

What is an astronomical unit?

The distance between the earth and the sun, used to track light years. One light year is equal to 63,200 AU. It takes slightly more than 8 minutes to travel 1 astronomical unit, which means the latest news we receive from the Sun is always 8 minutes old.

What is a light-year?

The distance light travels during one year.

What is the ecliptic?

The ecliptic is the plane of Earth's orbit around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year

What is our motion in the Universe?

The entire universe is expanding. Essentially all galaxies we see are moving away from us. The speed at which they are moving away is proportional to their distance; more distant galaxies appear to be moving away faster than closer galaxies.

What are the phases called?

The four main Moon phases in order are the New Moon, First Quarter Moon, Full Moon and Last Quarter Moon. These phases occur at very specific times and are measured by both the Moon's luminosity and how far along the Moon is in its orbit around Earth.

What does it mean when something is in orbit about a center of mass?

The orbit does depend on mass because it exerts a pull on the object around which it orbits. If two Earth mass bodies were orbiting each other, ignoring the gravity ofother bodies, the barycenter of the system would be perfectly in between them.

What causes the phases of the Moon?

The phases of the moon are actually just a result of our perception of the moon's half-illuminated surface. When the moon does pass through Earth's shadow the result is a lunar eclipse. This can be spectacular as the moon turns a deep shade of red.

What is acceleration?

The rate at which velocity changes.

How do we use continuous thermal spectra to learn temperature?

The shape of a star's thermal continuous spectrum is determined primarily by the temperature at the photosphere. The absolute brightness depends also on the radius of the photosphere. In a supernova, the temperature and radius of the photosphere change with time.

What does it mean that some constellations are in the zodiac?

The term zodiac is mostly associated with astrology, with the 12 signs of the western zodiac corresponding to the 12 constellations seen along the ecliptic.

What causes the seasons?

The tilt of the Earth's axis.

Kepler's Third Law of Motion

This law states that If you know the planet's distance from the sun you can find how long it takes to orbit the sun. Or, the square of a planet's orbital period is directly proportional to the cube of the semimajor axis of its orbit

What is the precession of the Earth's spin?

This motion is called precession, or "precession of the equinoxes". The Earth's spin causes it to be slightly flattened at the poles relative to the equator. Precession occurs because the Sun's gravity induces torque, or angular force, which pulls the Earth's equatorial bulge toward the ecliptic.

What phase is the Moon in for a lunar or solar eclipse?

Total lunar eclipse composite image by Fred Espenak. A solar eclipse happens at new moon, when the moon passes between the sun and Earth. A lunar eclipse happens at the opposite moon phase - at full moon - when the Earth, sun and moon align in space, with Earth between the sun and moon

What are partial, total, penumbral, and annular eclipses?

Total: This total eclipse happens about every year and a half somewhere on Earth. A partial eclipse, when the Moon doesn't completely cover the Sun, happens at least twice a year somewhere on Earth. Penumbral: The penumbra is the lighter outer shadow cast by the Moon or Earth. During a solar eclipse, viewers inside the penumbra see a partial solar eclipse. The Moon's color changes to a reddish or grayish tint when the Earth casts its penumbra shadow across the Moon. Annular: An annular eclipse occurs when the Sun and Moon are exactly in line with the Earth, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the dark disk of the Moon. A hybrid eclipse (also called annular/total eclipse) shifts between a total and annular eclipse.

What was the historical role of Tycho Brahe?

Tycho Brahe created a model of the solar system which would combine what he saw as the mathematical benefits of the Copernican system with the philosophical and "physical" benefits of the Ptolemaic system. It is essentially a geocentric model (with the Earth at the center of the universe), around which revolves the Sun, and around the Sun revolves the other planets.

What is wavelength and frequency?

Wavelength is the distance between crests (in nm). Frequency is how many cycles per second (s^-1). You can interchange between s-1 and Hz.

Example of: Angular momentum staying the same

When an ice-skater goes for a spin she starts off with her hands and legs far apart from the center of her body. But when she needs more angular velocity to spin, she gets her hands and leg closer to her body. Hence, her angular momentum is conserved, and she spins faster.

How is light like a wave?

When light moves from one medium (like air) to another medium (like water) it will change directions. This is a "wave-like" behavior and is called refraction. In this way light behaves like other waves such as sound waves. The speed of the light wave also changes when it moves from medium to medium.

Can you draw diagrams to show about what time a full moon rises, etc.?

Yes, study image.

How does your weight on a planet depend on the planet's size and mass?

Your mass doesn't change on other planets, but the gravity and size of those planets affect how much you weigh. So, your weight depends upon the gravity of the planet and your weight keeps changing based on planet gravity. The amount of gravity depends on the size of the planet.

What is the umbra and what is the penumbra?

umbra is the distinctly sharp area of the shadow. Penumbra is the unsharp shadow surrounding the Umbra.