Astronomy Midterm 1

Cosmic Address

The hierarchical structure of the universe, from Earth to the largest known structures, such as superclusters and filaments.

Local Group

A group of galaxies that includes the Milky Way and about 54 other galaxies, which are gravitationally bound together.

Virgo Supercluster

A massive supercluster of galaxies that contains the Local Group and many other galaxy groups and clusters.

Most Abundant Elements in the Universe

The elements that are most commonly found in the universe, including hydrogen, helium, and oxygen.

Human Appearance in the History of the Universe

If the history of the Universe was 1 year, humans would appear in the very last second of the very last day (December 31).

Telescopes as Time Machines

Telescopes allow us to see objects as they were in the past because light takes time to travel from distant objects to reach us.

Speed of Light in the Universe

Light moves at a finite speed, and it takes time for light from distant objects to reach us.

Scientific Notation

A method of writing numbers as a product of a number between 1 and 10 and a power of 10, used to represent very large or very small numbers.

Celestial Sphere

An imaginary sphere surrounding Earth on which all celestial objects appear to be located.

Zenith

The point directly above an observer's head on the celestial sphere.

Horizon

The line where the celestial sphere appears to meet the Earth's surface.

Celestial Poles

The points about which the celestial sphere appears to rotate, located at the intersection of the celestial sphere with the Earth's polar axis.

Celestial Equator

A great circle on the celestial sphere that is 90 degrees from the celestial poles, where the celestial sphere intersects the plane of the Earth's equator.

Altitude

The angle of a celestial object measured upwards from the observer

What number is our planet

Earth is the 3rd planet

Azimuth

The angle measured along the hoprizon from north around to the right to a point on the horizon below the point in the sky

Equatorial system

Describes the sky is universal, all people at all locations on eartb would record the same position for a star

How do stars move in the sky over a 24 hour period

Due to earths rotation, however the stars in our galaxy are all orbiting in nealry a circular path around the center of the galaxy

Motion of stars

Celestial equator: stars are looking east/west ( move straight/vertically )

North pole: stars circle the zenith ( circular motion )

Latitude: overhead

Ecliptic

annual path of the sun on the celestial sphere ( planet, sun, moon move along the ecliptic, they trace the plane of our solar system )

Keplers 1st law

Planetary orbit are ellipses ( not perfect circles ) with the sun at one focus

Keplers 2nd law

Planets move faster when they are closer to the sun, move slower when they are farther away

Keplers 3rd law

The larger the orbital path the longer the orbital period.

Newtons 1st law

Objects at rest stay at rest. Objects in motion stay in motion unless acted on by an outisde force

Newtons 2nd law

A change in the motion of an object is proportional to and in the direction of the force applied to it

Newtons 3rd law

For every motion there is an equal opposite reaction

Mass

Measure of the amount of material within an object

Volume

Measure of the amount of space an object or material occupies

Density

mass / volume = the amount of material per unit volume

Newtons Law of Universal Gravitation

Every planet or mass is kept in orbit by gravity ( force between bodies ).

Increasing the mass > increasing the force of gravity

Increasing distance > decreasing the force of gravity

Prehelion / Perigee

Planet is closest to the sun in its orbit ( moves faster )

Aphelion / Apogee

The planet is farthest to the sun in its orbit ( moves slower )

Dwarf planet orbits

Orbits are inclined with respect to the orbital plane

Comets

Have larger, more eccentiric ( less circular ) orbits than asteroids and planets

How fast must an object be moving to leave Earth’s gravitational pull?

Escape velocity, or escape speed, is the speed an object must be moving to overcome the earth’s gravitational pull.

more massive planets = faster escape speeds to escape their gravitational pull

The use of right ascension and declination to map the sky?

Used to describe positions in the sky of all kinds of astronomical bodies

How does the tilt of earths axis cause the seasons

Earth is tilted about 23.5 degrees, Caused by a change in the incidence angle of sunlight at different points in the earth’s orbit around the sun. the earth’s axis points towards the sun ( it is summer for that hemisphere ). When the earth’s axis points away it is winter.

Seasonal differs with latitudes?

At the poles > summer solstice (sun never sets) winter solstice ( sun never rises )

Equator > days are 12 hours round

Elsewhere (intermediate latitudes) > days are longer in summer, shorter in the winter. Extreme seasonal variation depends on proximity to the poles

What causes the phases of the moon

As the moon goes around the earth different parts of the moon are illuminated by the sun, hence we see different phases from differnt perspectives as the moon orbits theeartg.

How long does the moon take to rotate once on its axis ?

27.32 days

How long does the moon take to revolve around the earth one time ?

29.53 days

What is the dark side of the moon? explain how this relates to the time it takes for the moon to rotate once on its axis and revolve around the earth once.

The dark side of the moon Is the side of the moon facing away from the earth that doesn't get sunlight.

Lunar eclipse

can occur during a full moon, the moon passes all or a portion of the earth’s shadow.

Why does the moon look red during a lunar eclipse?

Sunlight reaching the moon passes through the earth’s atmosphere. The more dust or clouds in earth’s atmosphere during the eclipse the redder the moon will appear.

Frequency

measures how far a wave or crest passes a particular point longer the wave → lower frequency shorter wave → higher frequency

Speed of light ?

300,000,00 m/s

Light a particle or wave ?

Light is both a particle and wave

How does light behave as a particle? what is the name of a light particle?

The way light interacts with atoms (the photoelectric effect). A photon carries a specific amount of energy, related to the wavelength of the light

Shorther wavelength= more energy

Longer wavelength= less energy Proportion

Proportion of Light

The further you are from a source of light, the weaker the light will get.

Weins law

Hotter objects > emit shirter wavelengths, more energetic, electromagnetic radiation

Cooler objects > emit longer wavelengths, less energetic, electromagnetic radiation

Reflection

light reflects off smooth surfaces

Refraction

Light bends when moving through diff materials

Dispersion

Light can be sperated into its constituent colors bc diff lcolor of lights get bent diff

Spectrometers

are used to disperse light to form a spectrum. with this spectroscopy, we can identify the chemical composition of matter hence determining its physical structure.

Emission lines

are formed when electrons move down an energy level and emit a photon. Produced when specific elements emit photons or light

Absorption lines

are formed when an electron absorbs a photon and moves up an energy level. Caused when a continuous spectrum passes a hot thin cloud of gas and elements absorb specific wavelengths or colors of light.

Doppler effect

Objects moving towards you will shift to shorter wavelengths of light so they will appear bluer or blueshift

Objects moving away from you will shift towards longer wavelengths so they will appear redder or redshift

Aperture

The diameter of the opening of the telescope.

bigger aperture = more light collecting area, makes image brighter shaper and more detailed

What is a Charge-coupled Device (CCD) and how are they used in astronomical imaging?

• CCD records digital images.

• Photons hit the CCD surface. CCD records where photons hit and how many hit each pixel. (more pixels-higher quality image)

What are the advantages of putting telescopes in space?

above earth atmosphere = better seeing (no atmospheric turbulence)

Some types of light can only be observed from space because our atmosphere is opaque to light at those wavelengths

What types of light are only observable from space?

High energy ( ultraviolet, X-ray, Gamma-ray) and most infrared observing must be done from space