Astronomy

oort cloud

noun

/ˈuːət klˈaʊd/

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a distant, hypothetical region surrounding the solar system, thought to harbor icy bodies and comets

corona

noun

/kɜ.roʊ.nə/ or /kē.rooo.nē/

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the outer layer of the Sun's atmosphere, observable as a plasma halo during a solar eclipse

ecliptic

noun

/ɪk.lɪp.tɪk/ or /ik.lip.tik/

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the apparent path that the Sun traces in the sky over the course of a year, which is also the plane of the Earth's orbit around the Sun

parallax

noun

/pɛ.rə.læks/ or /pe.rē.lāks/

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the apparent displacement or difference in the apparent position of an object when viewed along two different lines of sight, often used in astronomy to measure the distance of nearby stars

pulsar

noun

/pʊl.sɜr/ or /pool.sēr/

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a highly magnetized, rotating neutron star that emits beams of electromagnetic radiation from its magnetic poles

astronomical unit

noun

/ɐstɹənˈɑːmɪkəl jˈuːnɪt/

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a unit of measurement equal to the average distance between the Earth and the Sun, approximately 149.6 million kilometers

parsec

noun

/pɑr.sɛk/ or /paar.sek/

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a unit of astronomical distance equivalent to about 3.26 light-years

cosmic ray

noun

/kˈɑːzmɪk ɹˈeɪ/

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a high-energy particle, mainly originating from outside the Solar System, that travels through space at nearly the speed of light

cosmic microwave background

noun

/kˈɑːzmɪk mˈaɪkɹoʊwˌeɪv bˈækɡɹaʊnd/

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(cosmology) the faint glow of radiation spreading through the universe, believed to be residual radiation from the Big Bang

nebular hypothesis

noun

/nˈɛbjʊlɚ haɪpˈɑːθəsˌɪs/

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(cosmology) a theory proposing that the solar system formed from a rotating nebula of gas and dust about 4.6 billion years ago

Hubble constant

noun

/hˈʌbəl kˈɑːnstənt/

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(cosmology) a measure of the rate at which the universe is expanding, determined from the observation of distant galaxies' recession velocities

interstellar medium

noun

/ˌɪntɚstˈɛlɚ mˈiːdiəm/

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the matter and radiation that exists in the space between stars within a galaxy

heliosphere

noun

/hɛ.lɪɑ:s.fɪr/ or /he.liaas.fir/

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the space surrounding the Sun dominated by solar wind

cosmic dust

noun

/kˈɑːzmɪk dˈʌst/

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very small particles originally derived from stars, serving as raw material for forming planets, and existing between galaxies, stars, and other celestial bodies

inflation

noun

/ɪnf.leɪ.ʃən/ or /inf.lei.shēn/

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(cosmology) the rapid expansion of the universe following the Big Bang

magnetic storm

noun

/mæɡnˈɛɾɪk stˈoːɹm/

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a disruption in earth's magnetic field caused by solar activity, resulting in variations that can impact electronic systems and communications on earth

aurora australis

noun

/ɐɹˈoːɹə ɔːstɹˈɑːliz/

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the colored lights, mainly green and red, in the sky seen primarily near the southern magnetic pole

cosmogonic

Adjective

/kɑ:z.mə.gɑ:.nɪk/ or /kaaz.mē.gaa.nik/

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associated with the phenomena, processes, or theories related to the origin and formation of the universe or celestial bodies

extragalactic astronomy

noun

/ˌɛkstɹəɡɐlˈæktɪk ɐstɹˈɑːnəmi/

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study of celestial objects outside the Milky Way galaxy

nebular

Adjective

/nɛ.bjʊ.lər/ or /ne.byoo.lēr/

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relating to or resembling a nebula, which is a cloud of gas and dust in outer space

sidereal

Adjective

/saɪd.riəl/ or /said.riēl/

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relating to the stars or constellations, especially in terms of their positions relative to Earth