Introduction to Astronomy: Telescopes, Light, and Celestial Motions

Comprehensive review flashcards covering telescope designs, detectors, electromagnetic radiation, spectral analysis, the Bohr atom, the Doppler effect, coordinate systems, seasons, calendars, lunar phases, tides, and eclipse mechanics.

The astronomical telescope was originally invented in the year __________.

$$1608$$

In the optical diagram shown, the telescope design that collects starlight using a curved mirror at the bottom is a __________.

reflector

In a Cassegrain focus reflecting telescope, the secondary mirror reflects light through a hole in the __________.

primary mirror

A telescope's light gathering power is proportional to the __________ of the primary lens or mirror.

square of the size

The optical defect where different colors of light are refracted to different focal points by a lens is known as __________.

chromatic aberration

Completed in 1897 at the University of Chicago's Yerkes Observatory, the world's largest refracting telescope features a lens measuring __________ inches in diameter.

$$40$$

Completed in 1948 on Mt. Palomar, the Hale Telescope was built with a primary mirror measuring __________ inches in diameter.

$$200$$

To overcome the atmospheric blurring known as 'seeing', astronomers use computer-controlled deformable mirrors in a system called __________ optics.

active/adaptive

While photographic plates record only about $1\%$ of incoming light, modern charge-coupled devices (CCDs) record __________ of incident light.

$$60\text{--}70\%$$

In the 1930s, Karl Jansky discovered radio emission from the galactic center that repeated 4 minutes earlier each day, corresponding to Earth's __________ period.

sidereal

The observational method of combining signals from multiple separate radio dishes to synthesize the resolution of a telescope the size of their separation is called __________.

interferometry

Following the 1988 collapse of the 300-foot Green Bank Telescope, the replacement 100-meter fully steerable dish completed in 2000 was named the __________ Radio Telescope.

Robert C. Byrd

Until China completed the 500-meter FAST telescope in 2016, the largest single-dish radio telescope in the world was the 300-meter __________ Telescope.

Arecibo

Space-based infrared observatories such as IRAS and Spitzer require active cooling because an uncooled detector would emit its own __________.

infrared radiation

The Hubble Space Telescope, launched on April 24, 1990, operates above Earth's atmosphere with a primary mirror diameter of __________ meters.

$$2.4$$

Launched on December 25, 2021, the James Webb Space Telescope operates in an orbit beyond the Moon with a primary mirror measuring __________ meters.

$$6.5$$

Compared to the James Webb Space Telescope, the Nancy Grace Roman Space Telescope is uniquely designed with a much wider __________ to survey large areas of the universe quickly.

field of view

The speed of light in a vacuum ($c$) is equal to wavelength multiplied by frequency, which is __________.

$$300{,}000\,\text{km/sec}$$

In the particle description of light, photon energy is calculated by the formula $E = h\nu$, where $h$ is Planck's constant and $\nu$ represents __________.

frequency

The ejection of electrons from a metal surface when struck by photons of sufficient energy is known as the __________ effect.

photoelectric

X-rays span wavelengths from $0.01\text{ to }20\,\text{nm}$ and are typically emitted by objects with temperatures between __________.

$$10^6\text{ and }10^8\,\text{K}$$

Ultraviolet radiation covers wavelengths from $20\text{ to }400\,\text{nm}$ and is typically emitted by supernova remnants and __________.

very hot stars

In the blackbody radiation curves shown, the wavelength of maximum emission ($\lambda_{\text{maximum}}$) shifts toward shorter wavelengths as the temperature __________.

increases

The Stefan-Boltzmann law indicates that the total energy radiated per second by a blackbody is proportional to the __________ power of its temperature.

fourth

According to Kirchhoff's laws, a continuous spectrum containing all wavelengths without interruption is produced by an incandescent solid, liquid, or __________.

dense gas

An emission spectrum consists of bright spectral lines at discrete wavelengths and is emitted by an excited, __________.

diffuse gas

An absorption spectrum featuring dark lines is created when continuous light passes through a __________ gas.

cooler

An atom that has the same number of protons but a different number of neutrons in its nucleus is classified as an __________.

isotope

When an atom gains or loses electrons, its mass remains virtually unchanged but its net electrical __________ changes, creating an ion.

charge

In the Bohr model of the hydrogen atom, electron transitions that drop down to the lowest orbit ($n = 1$) produce ultraviolet lines known as the __________ series.

Lyman

Transitions in a hydrogen atom between higher energy levels and the second energy level ($n = 2$) produce visible lines known as the __________ series.

Balmer

The astronomical Doppler effect only detects motion that is directed along the observer's __________.

line of sight

If an astronomical object's spectral lines are shifted toward longer wavelengths (a red shift), the object is __________ the observer.

moving away from

A spectral line with rest wavelength $\lambda_0 = 656.3\,\text{nm}$ observed at $\lambda = 656.5\,\text{nm}$ corresponds to a radial velocity of recession equal to __________.

$$91.4\,\text{km/sec}$$

On Earth, __________ is the angular distance measured north or south from the equator.

latitude

In the celestial equatorial coordinate system, Right Ascension is measured eastward from the vernal equinox in units of __________.

hours

The long, freely oscillating device shown that demonstrates the rotation of the Earth beneath its swinging plane is called a __________.

Foucault pendulum

The underlying astronomical cause of Earth's seasonal temperature changes is the __________ tilt of Earth's rotational axis.

$$23.5^\circ$$

The variation in distance between Earth and the Sun during its elliptical orbit is only about __________, ruling it out as the cause of seasons.

$$3\%$$

At geographic locations situated precisely on the Tropic of Cancer or Tropic of Capricorn, the Sun reaches the zenith on exactly __________ day(s) a year.

one

The June 21 summer solstice is not the hottest day of the summer in the northern hemisphere because it takes time to __________.

warm the Earth after a cold winter

Earth's true rotation period relative to distant stars (a sidereal day) is exactly __________.

$$23\text{ hours }56\text{ minutes}$$

The length of one tropical solar year is approximately __________ days.

$$365.2422$$

The Julian calendar introduced by Julius Caesar accumulated an error of about 11 minutes per year because it assumed a year was exactly __________ days.

$$365.25$$

When Pope Gregory XIII reformed the calendar in 1582 to restore the equinox, the day immediately following October 4 became __________.

October 15

The Moon requires $27.3\,\text{days}$ to complete one orbit around Earth (sidereal month), but takes __________ days to complete a full cycle of lunar phases (synodic month).

$$29.5$$

Because the Moon is in synchronous rotation, the side facing away from Earth was completely hidden from human observation until the Soviet spacecraft __________ photographed it in 1959.

Luna 3

In the diagram shown, when the gravitational tidal bulges of the Moon and the Sun align along the same axis, Earth experiences a __________.

spring tide

In the eclipse shadow diagram shown, the completely dark central conical shadow region (labeled 1) where sunlight is completely blocked is the __________.

umbra

Eclipses repeat in a predictable cycle known as the Saros cycle, which has an interval of exactly __________.

$$18\text{ years, }11\text{ days, }8\text{ hours}$$