Astronomy: Understanding Time and Calendars

<p>The time equal to $9,192,631,770$ periods of radiation corresponding to the transition between two levels of the hyperfine structure of the ground state of the caesium 133Cs atom. (B)</p> Signup and view all the answers

<p>Clocks moving relative to an observer appear to run slower. (C)</p> Signup and view all the answers

<p>Time runs slower for an observer in a stronger gravitational field. (C)</p> Signup and view all the answers

<p>The hour angle of the (mean) vernal equinox. (D)</p> Signup and view all the answers

<p>It is a mathematical point of the celestial sphere. (A)</p> Signup and view all the answers

<p>The date is advanced by one day. (A)</p> Signup and view all the answers

<p>Lunar calendar (A)</p> Signup and view all the answers

<p>The sidereal time, which equals the object's right ascension at upper culmination. (D)</p> Signup and view all the answers

<p>CET = UT + 1h, EET = UT + 2h (D)</p> Signup and view all the answers

<p>29.530589 days (B)</p> Signup and view all the answers

<p>10 hours (D)</p> Signup and view all the answers

<p>$86400.0009 s$ (B)</p> Signup and view all the answers

<p>The precessional motion of the vernal equinox. (A)</p> Signup and view all the answers

<p>0.0084 seconds (B)</p> Signup and view all the answers

<p>$365.242190 d$ (B)</p> Signup and view all the answers

<p>$t - λ = const$ (A)</p> Signup and view all the answers

<p>To align the date change with midnight. (A)</p> Signup and view all the answers

<p>Mean solar time at Greenwich meridian (C)</p> Signup and view all the answers

<p>Sundial (A)</p> Signup and view all the answers

<p>Two successive lower culminations of the Sun. (A)</p> Signup and view all the answers

<p>18 hours (B)</p> Signup and view all the answers

<p>W m$^{-2}$ rad$^{-2}$ Hz$^{-1}$ (B)</p> Signup and view all the answers

<p>The net energy flow across an area per unit time in a spectral range (C)</p> Signup and view all the answers

<p>Flux emitted by a black body and its temperature (B)</p> Signup and view all the answers

<p>5780 K (C)</p> Signup and view all the answers

<p>Stars do not radiate as black bodies. (C)</p> Signup and view all the answers

<p>The radiation is isotropic. (C)</p> Signup and view all the answers

<p>John C. Mather (B)</p> Signup and view all the answers

<p>A local quantity representing the temperature a black body would need to have in order to emit the same total amount of radiation (B)</p> Signup and view all the answers

<p>Terrestrial Time (TT) (C)</p> Signup and view all the answers

<p>It indicates the standard offset for Terrestrial Time from International Atomic Time. (C)</p> Signup and view all the answers

<p>Universal Time (UT) (A)</p> Signup and view all the answers

<p>Polar motion of the Earth (D)</p> Signup and view all the answers

<p>As the difference between Terrestrial Time and UT1. (A)</p> Signup and view all the answers

<p>It was the last adjustment to account for Earth's rotational variations. (A)</p> Signup and view all the answers

<p>An idealized body that absorbs all incident electromagnetic radiation. (A)</p> Signup and view all the answers

<p>Radiation emitted by a black body in thermal equilibrium with its environment. (C)</p> Signup and view all the answers

<p>By measuring the angular diameter and total flux (D)</p> Signup and view all the answers

<p>It depends on the stellar radius and distance (A)</p> Signup and view all the answers

<p>Lunar occultations (D)</p> Signup and view all the answers

<p>It indicates that measurements are accurate even at great distances (A)</p> Signup and view all the answers

<p>Photomultiplier and time step (A)</p> Signup and view all the answers

<p>Diffraction at an opaque barrier (C)</p> Signup and view all the answers

<p>The brightness of a star as perceived from Earth (D)</p> Signup and view all the answers

<p>The angular diameter based on stellar radius and distance (A)</p> Signup and view all the answers

A system for measuring time based on astronomical phenomena.

Defined as 9,192,631,770 radiation periods of caesium 133.

Time defined by the hour angle of a specific astronomical object.

Time is perceived to pass slower for objects in motion.

Time runs slower in stronger gravitational fields.

Time defined by the hour angle of the mean vernal equinox.

Days, months, and years are independent astronomical measures.

The period it takes for Earth to spin once on its axis.

The time interval between two successive culminations of the vernal equinox.

Sidereal day is 23h 56m 04.0914s long due to Earth's rotation.

A diagram showing the position of the sun at the same time each day throughout the year.

The time it takes for the Earth to complete one rotation around its axis, 23h 56m 04.0998s.

Mean solar time at the Greenwich meridian, used as a time standard.

The difference in time between the sidereal day and Earth's rotation period, which is 0.0084s.

Region of the Earth that has the same standard time.

The time based on the position of the Sun, calculated as Tₙ = tₙ + 12h.

The point at which an astronomical object is at its highest point in the sky.

Time zone that is 1 hour ahead of Universal Time during winter.

The interval between two consecutive lower culminations of the Sun.

An imaginary line where the date changes when crossed.

The angular measurement of time since a celestial object's upper culmination, often related to true solar time.

Calendar based on the phases of the moon, such as new or full moons.

A calendar year based on the Earth's orbit around the sun, approximately 365.242 days.

The time between successive new moons, about 29.530589 days.

The proper time of an observer moving with the Earth, affected by relativistic time dilation from Earth's orbital speed.

The standard time scale adopted in 1991, equivalent to TDT and defined as TT = TAI + 32.184 s.

The primary global time standard, regulating clocks and time based on Earth's rotation adjustments.

A form of Universal Time that accounts for polar motion.

The difference between Terrestrial Time (TT) and Universal Time (UT1), represented as ΔT = TT - UT1.

An extra second added to UTC to keep it in sync with Earth's rotation, the last was on December 31, 2016.

An idealized object that absorbs all electromagnetic radiation and emits black-body radiation when in thermal equilibrium.

The temperature of a star derived from its total flux and angular diameter.

A fundamental principle stating that energy cannot be created or destroyed.

The total amount of energy emitted by a star per unit time.

The space between the Earth and the observed star.

The angle that an object appears to occupy in the sky.

When the Moon passes in front of a star, blocking its light.

The bending of waves around obstacles, affecting angular measurement.

A research reference used for deriving effective temperature methods.

Describes the spectral distribution of electromagnetic radiation from a black body.

The electromagnetic radiation emitted by an idealized perfect absorber at thermal equilibrium.

The total energy radiated per unit surface area is proportional to the fourth power of the temperature.

A measure of a star's radiative output based on its emitted spectrum.

The power per unit area per unit solid angle per unit frequency emitted by a source.

Net energy flow across an area in a specified direction over time in a spectral range.

Awarded to John C. Mather and George F. Smoot for discoveries in the cosmic microwave background radiation.

The effective temperature of the Sun is approximately 5780 K.