astronomy unit 1

https://docs.google.com/document/d/1jNTBQRU655YQwXrrojZ_AmXp-kbI48rsiSppQfVRln0/edit?tab=t.0 and https://docs.google.com/presentation/d/1g2g8VEz_aeVMl3xvWRDSDmo94lI2vvoK/edit?slide=id.p22#slide=id.p22

Describe what astronomers mean by the universe and compare the sizes of its main components.

Astronomers define the universe as everything that exists: all space, time, matter, and energy. The universe is organized into structures of increasing size. Planets orbit stars, stars form solar systems, solar systems are part of galaxies, and galaxies are grouped into clusters and superclusters. Because the universe is extremely large, astronomers measure distances using light-years, the distance light travels in one year.

Distinguish scientific theories, hypotheses, predictions, observations and describe how scientists combine observation, theory and testing in their study of the universe.

An observation is something scientists measure or detect. A hypothesis is a testable explanation for those observations. A prediction describes what should happen if the hypothesis is correct. A scientific theory is a well-tested explanation supported by many observations and experiments. Scientists study the universe by making observations, developing theories, testing predictions, and revising ideas when new evidence appears.

Describe the celestial sphere, and explain how astronomers use constellations and angular measurement to locate objects in the sky.

The celestial sphere is an imaginary sphere surrounding Earth on which stars and planets appear to be fixed. Astronomers use constellations as reference patterns to map the sky. Objects are located using angular measurements, measured in degrees, which describe how far apart objects appear in the sky relative to one another.

Describe how and why the Sun and the stars appear to change position from night to night, from month to month and over thousands of years.

From night to night, stars appear to move because Earth rotates on its axis. From month to month, different constellations are visible because Earth orbits the Sun. Over thousands of years, Earth’s axis slowly changes direction due to precession, causing the positions of stars and constellations to shift over long periods of time.

Explain how Earth’s axial tilt causes the seasons, and why the seasons change over time as Earth precesses.

Earth’s axis is tilted about 23.5 degrees, which causes different parts of Earth to receive different amounts of sunlight during the year. This tilt produces the seasons, not Earth’s distance from the Sun. Over time, Earth’s axis slowly wobbles in a motion called precession, which changes the timing of seasons over tens of thousands of years.

Account of the exchanging phases of the moon, and explain how the relative positions of Earth, the Sun and the Moon lead to eclipses.

The phases of the Moon occur because we see different portions of the Moon’s sunlit half as it orbits Earth. Phases are not caused by Earth’s shadow. Solar eclipses occur when the Moon passes between Earth and the Sun, blocking sunlight. Lunar eclipses occur when Earth’s shadow falls on the Moon. Eclipses only happen when the Sun, Earth, and Moon line up correctly.

Explain how geometric reasoning can be used to measure the distances and sizes of otherwise inaccessible objects. 

The phases of the Moon occur because we see different portions of the Moon’s sunlit half as it orbits Earth. Phases are not caused by Earth’s shadow. Solar eclipses occur when the Moon passes between Earth and the Sun, blocking sunlight. Lunar eclipses occur when Earth’s shadow falls on the Moon. Eclipses only happen when the Sun, Earth, and Moon line up correctly.

Know the phases of the moon and terminology associated with the phases of the moon. 

The Moon’s phases follow a repeating cycle: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter, and waning crescent. Waxing means the lit portion is growing, and waning means it is shrinking.

Universe

All space, time, matter, and energy that exists

Astronomy

Study of objects and events beyond Earth

Light Year

Distance light travels in one year

Scientific Method

Process of observation, hypothesis, testing, and revision

Constellations

Recognized star patterns used to map the sky

Celestial Sphere

Imaginary sphere surrounding Earth where stars appear fixed

Celestial Poles

Points directly above Earth’s North and South Poles

Celestial Equator

Projection of Earth’s equator onto the sky

Solar Day

Time between successive noons (24 hours)

Sidereal Day

Time Earth takes to rotate once relative to the stars

Ecliptic

Apparent yearly path of the Sun across the sky

Zodiac

Constellations located along the ecliptic

Summer Solstice

Longest day of the year

Winter Solstice

Shortest day of the year

Seasons

Changes caused by Earth’s axial tilt

Equinoxe

Day when day and night are equal

Autumnal Equinoxe

First day of fall

Precession

Slow wobble of Earth’s axis over ~26,000 years

Moon Phases

Changing appearance of the Moon due to its position

Waning

Moon appears to shrink

Waxing

Moon appears to grow brighter

New Moon

Moon not visible from Earth

Crescent Moon

Less than half of the Moon is lit

Gibbous Moon

More than half of the Moon is lit

Lunar Eclipse

Earth’s shadow falls on the Moon

Solar Eclipse

Moon blocks sunlight from reaching Earth

Umbra

Darkest part of a shadow

Penumbra

Lighter outer part of a shadow

Parallax

Apparent shift of a nearby object due to a change in viewpoint

Maria

Dark, flat lava plains on the Moon

Craters

Bowl-shaped depressions caused by impacts

Highlands

Light-colored, mountainous regions on the Moon

Describe some of the observations made and models of the universe developed by ancient civilizations.

Ancient civilizations carefully observed the motions of the Sun, Moon, stars, and planets. Structures like Stonehenge show early understanding of solstices. Most ancient cultures supported a geocentric (Earth-centered) model, believing Earth was stationary and everything else moved around it.

Explain how the observed motions of the planets and the application of the scientific method led to our modern view of the Sun-centered solar system.

Planets sometimes appear to move backward in the sky, called retrograde motion. Geocentric models explained this using epicycles, but these models were complex and inaccurate. Applying the scientific method and better observations led astronomers to accept a heliocentric (Sun-centered) model, which explained planetary motion more simply and accurately.

Describe the major contributions of Copernicus, Galileo, Brahe, and Kepler to our understanding of the solar system.

• Copernicus proposed the heliocentric model

• Brahe made extremely accurate planetary measurements

• Kepler used Brahe’s data to discover mathematical laws of motion

• Galileo provided telescopic evidence supporting heliocentrism

State Kepler’s laws of planetary motion.

• Planets orbit the Sun in ellipses, with the Sun at one focus

• Planets move faster when closer to the Sun

• A planet’s orbital period is related to its distance from the Sun

Explain how astronomers have measured the true size of the solar system.

Astronomers measure distances using the astronomical unit (AU), the average Earth–Sun distance. Radar signals bounced off planets allow precise distance measurements, helping determine the true scale of the solar system.

State Newton’s laws of motion and universal gravitation and explain how they account for Kpler’s laws.

Newton’s laws of motion explain how objects move, and the law of universal gravitation explains the force attracting objects with mass. Together, these laws explain Kepler’s laws and show why planets move in predictable orbits.

Explain how the law of gravitation enables us to predict motions and measure the masses of astronomical bodies.

The law of gravitation allows astronomers to predict the motions of planets and moons and calculate their masses by observing how strongly they pull on other objects.

Stonehenge

Ancient stone structure in England aligned with solar events like solstices

Retrograde Motion

Apparent backward motion of a planet as seen from Earth

Geocentric

Earth-centered model of the universe

Epicycle

Small circular path used to explain retrograde motion in geocentric models

Deferent

Large circular path that epicycles moved along

Ptolemiac Model

Geocentric model using epicycles and deferents

Heliocentric

Sun-centered model of the solar system

Copernican Revolution

Shift from Earth-centered to Sun-centered view of the universe

Ellipse

Oval-shaped orbit of planets

Focus

One of two points inside an ellipse (the Sun is at one)

Semimajor axis

Half the longest diameter of an ellipse

Eccentricity

Measure of how stretched an orbit is

Period

Time required to complete one orbit

Astronomical Unit

Average distance between Earth and the Sun

Radar

Method using reflected radio waves to measure distances

Newtonian Mechanics

Laws describing motion and forces

Force

A push or pull

Weight

Force of gravity acting on an object

Inertia

Resistance to change in motion

Mass

Amount of matter in an object

Veloctiy

Speed and direction of motion

Gravity

Force of attraction between masses

Acceleration

Rate of change in velocity

Gravitational Force

Strength of gravity between two objects

Escape Speed

Speed needed to break free from gravity

Unbound

Not held by gravity

Orbits

Curved paths caused by gravity and forward motion

Aphelion

Point where an object is farthest from the Sun

Perihelion

Point where an object is closest to the Sun

Sidereal Year

Time Earth takes to orbit the Sun relative to the stars