Podcast
Questions and Answers
What causes the lunisolar precession of Earth's axis?
What causes the lunisolar precession of Earth's axis?
- The gravitational forces of the Moon and the Sun acting on non-spherical Earth. (correct)
- The magnetic field of the Sun interacting with Earth's core.
- The gravitational forces of the Moon and the Sun acting on Earth's perfect spherical shape.
- The gravitational forces of other planets in the solar system.
Approximately how long does one complete cycle of Earth's axial precession take?
Approximately how long does one complete cycle of Earth's axial precession take?
- 1,000,000 years
- 100,000 years
- 25,772 years (correct)
- 12,000 years
Why might the Sun not actually be located within the constellation corresponding to a zodiacal sign when we say it is?
Why might the Sun not actually be located within the constellation corresponding to a zodiacal sign when we say it is?
- The Sun's path varies randomly throughout the year.
- Precession of Earth's rotation axis and the division of sky into 88 constellations of different sizes. (correct)
- The zodiacal signs are based on a different calendar system.
- The constellations are shrinking in size over time.
How many constellations are officially recognized by the International Astronomical Union (IAU)?
How many constellations are officially recognized by the International Astronomical Union (IAU)?
Which zodiacal constellation is associated with the autumn season?
Which zodiacal constellation is associated with the autumn season?
Which coordinate system is commonly used for mapping planets and other solar system objects?
Which coordinate system is commonly used for mapping planets and other solar system objects?
In the Galactic coordinate system, what serves as the plane of reference (PoR)?
In the Galactic coordinate system, what serves as the plane of reference (PoR)?
What are the approximate equatorial coordinates ($\alpha$, $\delta$) of the North Galactic Pole?
What are the approximate equatorial coordinates ($\alpha$, $\delta$) of the North Galactic Pole?
What range of values does ecliptic latitude ($\beta$) span in the ecliptic coordinate system?
What range of values does ecliptic latitude ($\beta$) span in the ecliptic coordinate system?
Why are right ascension ($\alpha$) and declination ($\delta$) used in star catalogs and maps?
Why are right ascension ($\alpha$) and declination ($\delta$) used in star catalogs and maps?
Which of the following stellar properties can be directly determined using stellar parallax?
Which of the following stellar properties can be directly determined using stellar parallax?
What is the primary focus of astrophysics as a field of study?
What is the primary focus of astrophysics as a field of study?
In what part of the electromagnetic spectrum is X-ray astronomy conducted?
In what part of the electromagnetic spectrum is X-ray astronomy conducted?
What aspect of a star does its 'colour index' primarily indicate?
What aspect of a star does its 'colour index' primarily indicate?
Which of the following phenomena is primarily associated with the Earth's axial precession?
Which of the following phenomena is primarily associated with the Earth's axial precession?
What does the Hertzsprung-Russell (H-R) diagram plot?
What does the Hertzsprung-Russell (H-R) diagram plot?
Which observational technique is primarily used to measure the magnetic field of a star?
Which observational technique is primarily used to measure the magnetic field of a star?
Which of the following is the primary energy source of the Sun?
Which of the following is the primary energy source of the Sun?
What is the primary period of the most significant changes resulting from nutation?
What is the primary period of the most significant changes resulting from nutation?
Why is the daytime slightly longer than the nighttime during the equinox?
Why is the daytime slightly longer than the nighttime during the equinox?
What is the angle of inclination of the Moon's orbit relative to the ecliptic?
What is the angle of inclination of the Moon's orbit relative to the ecliptic?
At what time of year does the declination of the Sun ($δ_{☉}$) equal $+ε$?
At what time of year does the declination of the Sun ($δ_{☉}$) equal $+ε$?
Near the equator, how does the length of day and night vary throughout the year?
Near the equator, how does the length of day and night vary throughout the year?
What happens on the time scale of precession?
What happens on the time scale of precession?
What is the declination of the Sun around March 20th and September 22nd?
What is the declination of the Sun around March 20th and September 22nd?
What approximate rate does precession cause the cardinal points of the ecliptic to travel along the equator?
What approximate rate does precession cause the cardinal points of the ecliptic to travel along the equator?
Which of the following best describes the primary effect of precession?
Which of the following best describes the primary effect of precession?
What is the main cause of nutation?
What is the main cause of nutation?
How does precession affect the celestial coordinates of distant objects?
How does precession affect the celestial coordinates of distant objects?
What is the significance of specifying an epoch when providing celestial coordinates (α, δ)?
What is the significance of specifying an epoch when providing celestial coordinates (α, δ)?
Which of the following is true regarding the cardinal points of the ecliptic and precession?
Which of the following is true regarding the cardinal points of the ecliptic and precession?
If the right ascension (α) and declination (δ) of a star are given for the epoch 2000.0, and you want to find its approximate coordinates for the current year, which phenomenon do you primarily need to account for?
If the right ascension (α) and declination (δ) of a star are given for the epoch 2000.0, and you want to find its approximate coordinates for the current year, which phenomenon do you primarily need to account for?
What are the approximate ecliptic coordinates of the point in the sky located in the constellation Ophiuchus according to the diagram?
What are the approximate ecliptic coordinates of the point in the sky located in the constellation Ophiuchus according to the diagram?
What range does the declination ($δ$) span in the equatorial coordinate system?
What range does the declination ($δ$) span in the equatorial coordinate system?
What serves as the plane of reference (PoR) for the equatorial coordinate system?
What serves as the plane of reference (PoR) for the equatorial coordinate system?
Which of the following angles represents the axial tilt or obliquity ($\varepsilon$)?
Which of the following angles represents the axial tilt or obliquity ($\varepsilon$)?
What is the range of values for right ascension ($α$)?
What is the range of values for right ascension ($α$)?
In the context of celestial coordinates, what is the 'first point of Aries'?
In the context of celestial coordinates, what is the 'first point of Aries'?
What is the name of the angle measured along the celestial equator from the vernal equinox to the hour circle passing through an object?
What is the name of the angle measured along the celestial equator from the vernal equinox to the hour circle passing through an object?
If you have values for right ascension and declination, what coordinate system are you working with?
If you have values for right ascension and declination, what coordinate system are you working with?
What is the approximate value of the axial tilt or obliquity ($\varepsilon$)?
What is the approximate value of the axial tilt or obliquity ($\varepsilon$)?
Flashcards
Ecliptic Coordinates
Ecliptic Coordinates
Coordinates based on the plane of the ecliptic, used for Solar System bodies.
Ecliptic Longitude (𝛌)
Ecliptic Longitude (𝛌)
The angle measured along the ecliptic, ranging from 0º to 360º.
Ecliptic Latitude (𝛃)
Ecliptic Latitude (𝛃)
The angle measured from the ecliptic plane, from -90º to +90º.
Galactic Coordinates
Galactic Coordinates
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Galactic Center (l = 0°)
Galactic Center (l = 0°)
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IAU Constellations
IAU Constellations
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Lunisolar Precession
Lunisolar Precession
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Precession Period
Precession Period
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Zodiacal Constellations
Zodiacal Constellations
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Sun's Position in Zodiac
Sun's Position in Zodiac
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Astronomy
Astronomy
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Celestial Sphere
Celestial Sphere
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Coordinate Systems
Coordinate Systems
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Stellar Parallax
Stellar Parallax
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Hertzsprung-Russell Diagram
Hertzsprung-Russell Diagram
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Electromagnetic Spectrum
Electromagnetic Spectrum
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Photometry
Photometry
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Astrometry
Astrometry
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Hour Angle (t)
Hour Angle (t)
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Tan Formula for Hour Angle
Tan Formula for Hour Angle
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Azimuth (A)
Azimuth (A)
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Tan Formula for Azimuth
Tan Formula for Azimuth
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Altitude (h)
Altitude (h)
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Declination (δ)
Declination (δ)
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Right Ascension (𝛂)
Right Ascension (𝛂)
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Plane of Celestial Equator
Plane of Celestial Equator
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Nutation period
Nutation period
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Precession of nodes
Precession of nodes
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Equinox
Equinox
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Atmospheric refraction
Atmospheric refraction
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Solar declination (δ)
Solar declination (δ)
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Length of day at equator
Length of day at equator
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Rises and settings of the Sun
Rises and settings of the Sun
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Tilt of Earth's axis
Tilt of Earth's axis
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Cardinal Points of Ecliptic
Cardinal Points of Ecliptic
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Precession
Precession
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Nutation
Nutation
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Celestial Poles
Celestial Poles
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Coordinate Change Rate
Coordinate Change Rate
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Epoch
Epoch
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Ophiuchus
Ophiuchus
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Study Notes
Astrophysics I Lecture 1
- Lecture 1 covers introductions, coordinate systems used in astronomy, and the annual motion of the Sun.
- Coordinate systems used in Astronomy are discussed in the presentations.
- The annual motion of the Sun is explained in lecture material
Astrophysics I & II Course Contents
- Astrophysics I
- An Introduction providing basic definitions, stellar parameters (4 hours)
- Tools of astrophysics (6 hours)
- The Sun (2 hours)
- Stellar atmospheres (8 hours)
- Stellar structure and evolution (10 hours)
- Astrophysics II
- Final stages of stellar evolution (8 hours)
- Close binary stars (6 hours)
- Solar system, extrasolar planets (4 hours)
- Galaxies (6 hours)
- Cosmology (6 hours)
Astrophysics I Lecture Times and Dates
- Lectures: Wednesdays, 4:00 PM EET/CET
- Classes: Mondays, 2:00 PM EET/CET (with Kamil Bicz)
- Academic year: 2024/2025 (October 1st, 2024 - February 21st, 2025)
Astrophysics: Lecture Contents
- Astronomy is an observational science, with astrophysics being a subset that uses physical laws.
- Celestial sphere coordinate systems are used in Astronomy.
- The annual motion of the Sun, precession and rises/settings of celestial bodies are included in the lecture notes.
- Astronomical calendars and related time systems.
- Blackbody radiation, stellar spectra, fluxes, and effective temperatures
- Stellar magnitudes (bolometric, luminosity, color index)
- Measurements of parallax, cosmic distance scale
- Stellar parameters (masses, radii) and the Hertzsprung-Russell diagram
Tools of Astrophysics (6 hours)
- Electromagnetic spectrum and observational windows
- Ground-based and space observatories
- Telescopes and detectors
- Infrared, ultraviolet, X-ray, gamma-ray astronomy
- Observing techniques (imaging, photometry, spectroscopy, optical and radio interferometry, astrometry, polarimetry)
Textbooks
- Fundamental Astronomy by H. Karttunen et al.
- An Introduction to Astrophysics by B. Basu et al.
- Astrophysical Concepts by M. Harwit
- Introduction to Modern Astrophysics by B.W. Carroll and D.A. Ostlie
Celestial Sphere: Elements of Spherical Astronomy
- Coordinate system components, including axes (X, Y, Z).
- Transformations between different coordinate systems.
- Spherical coordinates (r, ψ, φ)
- Coordinate conversions (x, y, z) and relations among coordinates.
- Descriptions using planes and circles.
- Formulas to convert from spherical coordinates to Cartesian coordinates
Celestial Sphere Introduction
- Plane of Reference (POR): A plane utilized to divide the sphere into hemispheres. This is a key concept that allows for dividing the sphere into hemispheres.
- Circle of Reference (COR): An initial semicircle.
- Two coordinates: Great and Small circles.
- Centre of the system (O): The origin point in the coordinate system.
An Example: Geographical Coordinates
- Plane of reference: plane of Earth's equator
- Circle of reference: equator
- Initial semicircle: Greenwich (prime) meridian
- Coordinates: longitude λ (traditional 0-180° E and 0-180° W), latitude φ (-90° to +90°), traditional 0-90° N and 0-90° S.
- Wrocław example: 51° 6′ N, 17° 2′ E
Spherical Triangle
- Relationships involving angles (α, β, γ) and sides (a, b, c).
- Spherical excess (ε) calculations
- Formulas for sine, cosine angles, cosine formulas are highlighted to define spherical triangles.
Systems of Coordinates: Location of the Centre
- Topocentric, Geocentric, Selenocentric, Planetocentric, Heliocentric, Barocentric, and Galactocentric
Horizontal System of Coordinates/Frame
- PoR: plane tangent to Earth's surface through the observer (O)
- CoR: horizon
- Vertical: great circle through zenith (Z)
- Nadir (Nd)
- Local meridian (ISC)
- Cardinal points, direction (N, S, E, W)
- First vertical
- Celestial North and South Pole
- Astronomical Meridian.
Horizontal System of Coordinates: Azimuth and Altitude
- Azimuth (A): angle measured along the horizon from the north direction (0°-360°)
- Altitude (h): Angle measured up from the observer's horizon and the object (–90° to +90°)
- Zenith distance (z): vertical angle between the object and the zenith (0° to 180°).
Equatorial System of Coordinates/Frame
- PoR: plane of celestial equator
- CoR: celestial equator, vertical
- P: celestial north pole
- P': celestial south pole
- ISC: Local meridian through Z
Equatorial System of Coordinates/Frame (II)
- Hour Angle(t): The angle between the vertical through Z and the vertical through the object G, measured along the celestial equator. 0°– 360° or 0h - 24h;
- Declination (δ): Angle between the plane of the celestial equator and the direction toward the object G; -90° to +90°.
Dependencies between Coordinates Frames
- Transformation matrix equations for coordinate conversions.
Ecliptic System of Coordinates
- Plane of reference (PoR): plane of ecliptic
- Circle of reference (CoR): The ecliptic
- Initial semicircle (ISC): great circle through vernal equinox.
- Coordinates Ecliptic Longitude (λ) and Ecliptic Latitude (β).
Constellations
- IAU-designated constellations (88) including northern and southern maps.
Lunisolar precession of Earth's axis
- Gravitational forces of the Moon and the Sunt
- Axis of rotation: Period of 26,000 years.
Annual motion of the Sun
- Cardinal points of the ecliptic.
- Descriptions of the vernal equinox (March 20–21), summer solstice (June 21), autumnal equinox (September 22–23), and winter solstice (December 21–22) in terms of right ascensions and declinations.
Changes of the Declination of Sun
- Negative declinations, between autumnal & vernal equinoxes (Sep - Mar)
- Positive declinations between vernal & autumnal equinoxes (Mar - Sep)
Ecliptic system of coordinates
- Ecliptic longitude (λ), defining the angle between the vernal equinox ray and an object G. Values from 0° to 360°.
- Ecliptic latitude (β), the angle between the ecliptic plane and an object G. Values from -90° to +90°.
Refraction
- Apparent change in altitude of objects in the Earth's atmosphere.
- Relationship between observed (h) and true (h₀) altitudes, and the refractive index (n) of the atmosphere.
Atmospheric Effects due to Refraction
- Effects on solar disc shape (deformation, flattening)
- Green flash phenomenon (at sunrise and sunset)
Other effects affecting apparent position: Parallax
- Apparent position difference of an object viewed from two different lines of sight.
- Trigonometric parallax measurement techniques.
- Heliocentric parallax and orbital motion of Earth
Other effects affecting apparent position: Aberration
- Apparent star shift caused by orbital motion of Earth and finite speed of light.
- Discovered by James Bradley to measure parallax.
- Relationship between observed (α), mean (α₀) position of object, speed of light and Earth's orbital velocity.
Aberration
- Location of the aberration and parallax ellipses relative to each other.
- Aberration of nearby and distant objects
Twilights and Dawns
- Gradual transitions from night to day defined by three types (civil, nautical, astronomical) based on horizon altitude.
- Twilight periods (civil, nautical, astronomical) defined by various horizon angles.
Solarigraphy
- Photographic technique for recording the Sun
Rises and Settings of the Sun
- Locations of upper culminations and lower culminations are discussed.
- Hour Angle (t) and Azimuth (A) are presented at the time of rising and setting events
Digression: Comet C/2023 A3 (Tsuchinshan-ATLAS)
- Information about comet path and position relative to other celestial bodies.
- Perihelion (closest point to the Sun) and closest approach to Earth provided.
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