Astronomy Concepts

World Geodetic System

• A parallel plane on the surface is not part of the World Geodetic System.
• A gravitational equipotential surface, standard coordinate system, and standard spheroidal reference surface are components of the system.

Reference Systems

• Horizontal and Equatorial systems share the East-West axis.

Vernal Point

• Vernal Point is defined as the intersection between the Equator and the Ecliptic.

Definition of Parsec

• Parsec is the distance at which one astronomical unit subtends an angle of one arc second.

The Sun's Motion

• The motion of the Sun on the Equator is not uniform because it moves on the Ecliptic.

Wrong Definition for Proposed Years

• Draconic year is not related to the Moon's passage on the Vernal Point.

Wrong Sentence on Spectral Lines

• Absorption lines are not formed when photons from a cold source pass through a hotter one.

Electromagnetic Spectrum Order

• Energy associated with a photon decreases with increasing wavelength.

Wrong Sentence on Color Index

• Color index is affected by the stellar radius or the distance of the star.

Wrong Sentence on Measurement of Radiation

• The total intensity is obtained by integrating the specific density over a solid angle.

Wrong Sentence on Spectrographs

• Echelle spectrographs allow for extremely high resolution, but only for ground instruments.

Wrong Sentence on Slit Spectroscopy

• Slit spectroscopy allows high spectral resolution but its complexity makes it not suitable for space telescopes.

Primordial Solar Nebula

• Hydrogen and Helium constitute 98% of the main components of the primordial solar nebula.

Differences Between Planets

• Planets have primitive atmospheres, outer planets have secondary atmospheres.

Earth's Atmosphere

• Nitrogen is the main component of the Earth's atmosphere.

Mass Dependency

• Radius of the main planet times the cubic root of the ratio of the densities of the two bodies.

Shepherd Satellites

• Small satellites orbit among Saturn's rings and other giant planets' rings.

Jupiter's Mass Compared to Earth

• Jupiter's mass is 317 times bigger compared to Earth.

Jovian planet gas

• Helium and Hydrogen dominate Jovian planets in terms of gas.

Cometary Formation

• Cometary ion tail forms due to the interaction between cometary ions and solar wind.

Thick Atmosphere Satellite

• Titan is a satellite in the Solar System with a thick atmosphere.

Main Sequence

• Main Sequence stars are randomly scattered all across the diagram.

Radiating as the Sun Lifetime

• Nuclear reactions keep a star in balance for billions of years only if all of its mass is converted to energy.

Massive Star Evolution

• Each nuclear burning phase converts the totality of the mass of the star in an element with higher atomic number.

Stars Nuclear Fusion

• In the Sun 99% of the energy is produced by the proton-proton chain, and 91% by the ppl chain

White Dwarf Sentences

• Electron degeneracy pressure can support a white dwarf of any mass, regardless of its origin.

Compact objects

• From the outside, the observer does not see the clock of someone falling into a black hole increasing its speed exponentially.

Sun Rotation

• The Sun rotates at the same angular velocity from its equator to the poles, and it can be approximated to a rotating rigid body

Sun Atmosphere

• The solar atmosphere is divided into the corona (300-500 km thick) and the photosphere (over 500 km). The chromosphere extends much further out

Definition of planet

• A planet/exoplanet can orbit another planet or float free in space

Classification of planet

• Candidate planet: a planet selected by the International Astronomical Union as a possible Earth 2.0

Galaxies Properties

• It is nearly impossible for galaxies to collide or merge. Structural properties are preserved since their formation

cluster associations

• The Messier and NGC catalogues include a careful selection of open and globular clusters, with all possible constellations and asterisms cleaned out

Propreties of galaxies

• Small galaxies do exist isolated from other galaxies, and they never orbit larger galaxies

exoplanets

• Warm Jupiter/Neptunes: gas giants with temperature adequate to host liquid water

White Dwarfs

• White dwarfs are very cold, so they are dim (low luminosity) despite their large size (several solar radii)

mean motion resonance

• Only a small number of neutron stars emits a radio beam sweeping the sky regularly, and all of them take the name of pulsars

mass-temperature relationship

• The CNO cycle is less sensitive to temperature, so in massive stars, nuclei reactions occur at a much slower rate

white dwarfs

• Electron degeneracy pressure can support a white dwarf of any mass, regardless of its origin

A star as the sun wrong statement

• Chemical reactions or radioactivity are not efficient enough to justify the luminosity of the Sun

hydrostatic equilibrium in stars

• Hydrostatic equilibrium is naturally realized without requiring any source of energy

The sun inner energy

• In the Sun, only 19% of the energy is produced within 0.25 solar radii. Every second four tonnes of mass are converted into energy

Magnetic activity

• The lifetime of a single spot can be of several years. Spots appear and disappear randomly on the on the of the Sun

wrong lifetimes

• Both the intensity and the peak frequency of a blackbody increase with decreasing temperature

The vorrect sentences

• During its lifetime, a massive star is able to burn all the hydrogen in the core and outside the core

Stellar clusters

• Open clusters and associations appear to be randomly distributed in the galactic disk, so they do not provide any information on the shape of the Milky Way

stellar evolution

• At the end of their life, low-mass stars will evolve into Carbon-Oxygen white dwarfs and slowly cool down

Prostar sentences

• During the protostar phase, the central temperature in the core is high enough for Hydrogen fusion