Astronomy 110 Exam 1

Accuracy

The degree to which a measured or calculated value corresponds to the true value. In astronomy, accuracy is crucial for obtaining reliable data and making precise observations.

Precision

The degree to which repeated measurements under unchanged conditions show the same results. Precision is important in astronomy for assessing the consistency of observations.

Horizion

The boundary between the sky and the ground/your surroundings

Nadir

The point directly beneath you, opposite the zenith

Altitude

How high an object is above the horizion

Azimuth

The direction around the horizion, typically measured from north to east

Celestial sphere

The celestial sphere is an imaginary sphere surrounding Earth onto which we imagine the stars and other celestial objects projected.

Celestial poles

Imaginary points where earth’s rotational axis extends into space, creating a North and South pole

Celestial Equator

Earth’s equator projected onto the sky

The Ecliptic

the apparent path of the Sun across the celestial sphere during the year.

Constellation

An officially recognized region of the sky

Asterism

A recognizable pattern of stars that is not necessarily an offical constellation

Retrograde Motion

Planets normally move eastward relative to the stars, but sometimes appear to temporarily move westward.

Aristotle

Earth-centered cosmos

heavenly objects associated with perfection

heavens considered unchanging

circular motions regarded as natural/perfect

Ptolemy

Developed a detailed geocentric model

Epicycle

A small circular motion superimposed on another circular motion

Deferent

The larger circle along which the center of an epicycle moves

Kepler

discovered that planets move in elliptical orbits, rather than perfect circles

Occam’s Razor

The general principle that, when multiple explanations account for the evidence, we should prefer the one that does not introduce unnecessary complexity

Two books model

Galileo argued that nature and Scripture could be thought of as two "books" that reveal truth in different ways.

Scientism

The view that scientific methods/science are the primary or exclusive reliable ways of obtaining knowledge.

Naturalism

generally holds that reality can be understood in terms of natural phenomena rather than supernatural causes.

Materialism

emphasizes physical matter/processes as fundamental.

Young-Earth Creationism

Generally holds that Earth and life are relatively young and that creation occurred through divine action as described by a particular interpretation of Genesis

Old-Earth Creationism

Accepts an ancient Earth but maintains that God played a direct role in creation.

Theistic Evolution

Accepts evolutionary science while maintaining that God is compatible with, or involved in, creation/evolution.

Intelligent Design

Argues that certain features of nature are best explained by an intelligent cause rather than solely by undirected natural processes.

Deism

The belief that God created the universe but generally does not intervene in its ongoing operation.

Kepler's First Law

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

Ellipse

An oval-shaped curve

Semimajor axis

Half the longest diameter of an ellipse

Eccentricity

Measures how stretched an ellipse is

Kepler's Second Law

A line connecting a planet to the Sun sweeps out equal areas in equal amounts of time.

Kepler’s Third LAw

For objects orbiting the same central body:

P^2=a^3 when P is measured in years and a in AU for objects orbiting the Sun.

Newton’s first law of Motion - inertia

An object remains at rest or moves at constant velocity unless acted upon by a net external force.

Newton’s Second Law of Motion

Force equals mass times acceleration.

Newton’s Third law of Motion

Forces come in equal and opposite pairs.

If object A exerts a force on object B, B exerts an equal and opposite force on A.

Rotation

An object spins around its own axis.

Revolution

An object travels around another object.

Waxing

The illuminated portion we see is increasing.

Waning

The illuminated portion we see is decreasing.

Lunar Cycle

Solar Eclipse

Moon comes between Earth and Sun.

Solar corona

The Sun's outer atmosphere, visible especially during a total solar eclipse.

Lunar Eclipse

Earth comes between Sun and Moon.

Umbra

The darkest central portion of a shadow

Penumbra

The lighter, partial-shadow region.

Tides

primarily caused by the gravitational effects of the Moon and Sun, with the Moon being the dominant contributor.

Reflection

Light bounces off matter.

Refraction

Light changes direction because its speed changes when it moves between materials.

Absorption

Matter takes in light energy.

Transmission

Light passes through matter

Emission

Matter releases light

Electromagnetic Spectrum

Radio → Microwave → Infrared → Visible → UV → X-ray → Gamma

Electron moves upward

It must absorb energy

Electron moves downward

It emits energy as a photon

Why do atoms have unique spectra?

Each type of atom has a unique set of allowed energy levels.

Therefore, each atom can absorb or emit particular photon energies.

This produces a unique spectral pattern — effectively a fingerprint of the atom.

Kirchhoff’s 1st law of spectroscopy - Continuous Spectrum

A hot, dense object produces a continuous spectrum.

Kirchhoff's 2nd Law of Spectroscopy - Emission Spectrum

A hot, low-density gas produces bright emission lines at specific wavelengths.

Kirchhoff's 3rd Law of Spectroscopy - Absorption spectrum

A cooler, low-density gas in front of a continuous-spectrum source produces dark absorption lines.

Blackbody

an idealized object that emits thermal radiation according to its temperature

Refractor telescope

Uses lenses to collect and focus light.

Reflector telescope

Uses mirrors to collect and focus light.

Aperture

the diameter of a telescope's primary light-collecting lens or mirror.

Why Build Bigger Telescopes?

greater light-gathering ability

ability to observe fainter objects

improved potential resolution

better observations of distant objects