What is Astronomy: Definition and 820 Discussions

Astronomy (from Greek: ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates outside Earth's atmosphere. Cosmology is a branch of astronomy that studies the universe as a whole.Astronomy is one of the oldest natural sciences. The early civilizations in recorded history made methodical observations of the night sky. These include the Babylonians, Greeks, Indians, Egyptians, Chinese, Maya, and many ancient indigenous peoples of the Americas. In the past, astronomy included disciplines as diverse as astrometry, celestial navigation, observational astronomy, and the making of calendars. Nowadays, professional astronomy is often said to be the same as astrophysics.Professional astronomy is split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects. This data is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. These two fields complement each other. Theoretical astronomy seeks to explain observational results and observations are used to confirm theoretical results.
Astronomy is one of the few sciences in which amateurs play an active role. This is especially true for the discovery and observation of transient events. Amateur astronomers have helped with many important discoveries, such as finding new comets.

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  1. A

    B Is there a standard mapping of celestial coordinates to geo-coordinates

    Sorry, I'm not an astronomer. This question relates to the book "S." by Doug Dorst. I understand that the celestial coordinates have a zero-point at the vernal equinox. (0h, 0m, 0s RA, 0⁰, 0", 0' Dec.) I also understand that it's possible to map these coordinates to spherical, or...
  2. C

    Courses Course advice for an enthusiast

    Hey all, firstly let me give some background, i`m a Cloud Computing Engineer and have been in the I.T. industry for the past 20 years since I left university. I have always had an interest in science and astronomy (My dad was a keen amateur astronomer) but never really taken it very seriously...
  3. C

    Observing galaxies: area of sky would I need to survey

    Homework Statement Given that there are 10-2 Ellipticals per Mpc3 and my garden telescope can reach to 14 mag. How large an area of sky would I need to survey to find 100 Elliptical galaxies ? (assume the typical absolute magnitude for an Elliptical galaxy is -21 mag).Homework Equations...
  4. C

    About initial mass function and mean mass in stellar cluster

    Homework Statement Assuming a Salpeter IMF with upper and lower mass limits of 0.1 and 20 M⊙ respectively, calculate: (i) the mass point at which half the mass formed in a stellar cluster lies in more massive systems and half in less massive systems. ii) the mass point at which half the...
  5. A

    Schools Which university to go to for a physics degree?

    I graduated from Georgia Tech a few years ago with a Bachelors in Applied Mathematics and now I am currently a software developer, however, my passion is in astronomy. I have looked at opportunities in astronomy that is towards the engineering route i.e. image processing engineer, detector...
  6. Vanadium 50

    I Bad astronomy = bad statistics?

    Phil Plait, creator of Bad Astronomy, has an article on Planet 9. Overall, it's pretty good, but there was one part that got my hackles up: It may be more clear, but at a cost of being more wrong.
  7. H

    What is the connection between organic chemistry, trigonometry, and astronomy?

    Hi, I am a retired Organic Chemist. I was looking around for the answer to a trig question and found this site. It looks interesting so I signed up. I am also an amateur astronomer, and have an interest in arduinos and raspberry pis as well as other computers. I mainly use linux and my...
  8. astroman707

    Admissions Phyics REU personal statement critiques?

    I just finished my personal statement for physics REU applications, and I was wondering if anyone would be willing to read it and give it some critiques or general advice. If accepted, this will be my first REU. I'm applying to 10 schools. Thanks! *** Physics never actually caught my eye until...
  9. James Beedy

    Comparing image sizes of the hotter stars with the cooler stars

    Homework Statement When comparing image sizes of the hotter stars with the cooler stars, do hotter stars consistently appear larger in one image and cooler stars consistently appear smaller in the other image? Why or why not? Homework Equations Stellar Spectra Classification[/B]The Attempt...
  10. kechloo

    B What Mysteries Lie Between the Galaxies?

    Hello, Well, first, I’m sorry if I’m doing mistakes in the english… (not my first language). I’m not profesionnal on physics and astronomy but I’m really curious. I have somes basics questions : Where is the place of our solar system in the milky way ? Is it possible to have like « physical...
  11. Brian Leist

    Admissions How to enter theoretical physics with astronomy background?

    Hi all, I am interested in advancing my education in theoretical physics, specifically topics concerning quantum field theories and quantum gravity. However, I have a somewhat rocky background as an early undergrad and while my Master's degree was achieved with great success in the classroom...
  12. A

    Astronomy Physics Extended Essay

    Hi, I was told today that I will be starting my EE (an EE stands for Extended Essay, where we have to write 4000 words research paper where you analyse data, do experiments etc... for a particular topic of your choice) One of my main areas of interest in physics is astronomy and I would like to...
  13. Fatima7

    Studying Medical (Radiography) and Astronomy

    Good morning, I would like to know if its possible to do my Master degree in any field related to space and astronomy, actually I graduated with bachelor of applied science (Medical Imaging). I deal with x-ray and imaging machines. My courses were somewhere between biology, x-ray (radiation)...
  14. P

    A Is there any astro-field that uses QM or GR frequently?

    Hi all! Happy New year! I will select my supervisor soon but i want to involve in the field that uses QM or GR frequently I love physics and i want to apply physics to explain astrophysical phenomenon. I know that Compact objects and Astrochemistry use such physics but i wonder to know more...
  15. astroman707

    Programs Is a 2nd major in comp sci useful in computational physics?

    I'm majoring in physics and I'm planning on pursuing computational astrophysics in graduate school. Will a second major in computer science/programming look good to graduate schools, and/or will it give me great advantages in the field of computational astrophysics or astronomy?
  16. sams

    A How to calculate Saturn's mass from Kepler's third law?

    This is not a homework. In Chapter 8: Central-Force Motion, in the Classical Dynamics of Particles and Systems book by Thornton and Marion, Fifth Edition, page 325, Problem 8-19, we are asked to calculate the mass of the planet Saturn. In the instructor's solution manual, the solution for this...
  17. astroman707

    Programs Difference between an astronomy and astrophysics PhD?

    Is there really much of a difference between an astronomy PhD and an astrophysics PhD? There seems to be a lot of overlap in the fields, and it seems that both can qualify you for many of the same careers, it just depends on the PhD focus. For an example, I'm very interested in almost all areas...
  18. D

    Dave Parham, Raleigh, NC, I love Science

    hi there, i have always loved Science, and from astronomy transitioned into particle physics because of the Higg Boson, learning about the implications of Dark Matter, and Dark Energy. i am also studying things like Zero Point Energy, have always been fascinated with the flight dynamics of...
  19. F

    I Correlation between a Star's Luminosity and Distance?

    I made three charts from several different sources plotting the luminosity and distance from Earth of 26 to 300 Stars. In each chart, there appears to be a correlation between a star's luminosity (in solar units) and its distance from Earth (or solar system, whichever you prefer) in light years...
  20. StillLearningToronto

    Astronomy- Initial Mass Function problem

    1. Homework Statement The Initial Mass Function (IMF) defines the distribution of stellar masses created in a star-forming event. The probability P(m)dm of forming a star with a mass between m and m + dm is given by P(m)dm = km−α dm where α is the exponent of the power law and k is a constant...
  21. starstruck_

    Spectrum of hot gas uniformly mixed with dust

    hey! EDIT: I didn’t post this in homework help because there aren’t any computational questions, it’s just conceptual My assignment scenario consists of a star (blackbody) surrounded by an expanding shell of hot gas. I’m given its spectrum and it is a continuous emission spectrum. Emission...
  22. Neha98

    Programs Applied or pure physics major is best for an astronomy career?

    I'm willing to make postgraduate studies in astronomy or astrophysics so which major is more suitable for me applied or pure phyics?
  23. Urmi

    What sparked my passion for physics?

    Hey guys! I'm Urmi and I'm just a regular teen who's crazy about Physics. Physics has been my area of interest since my step into middle school and now when I see TV Series like Stranger Things, I feel so darn good that kids nowadays (and in the 80s) dig science stuffs so freaking much. I dream...
  24. Frimus

    Astronomy A free Modern Introduction to Astronomy textbook

    Recently I found a real gem for astronomy enthusiasts and junior undergraduate students. It has a plenty of pictures, diagrams, links to other resources and visualizations. You can access this excellent up-to-date Astronomy textbook (cca 1200 pages) for free in web view or PDF. I have included...
  25. MichaelJT

    How Can an Undergraduate Physics Student Contribute to a Physics Forum?

    Hello! I am a current undergraduate physics student with a keen interest in primarily astronomy and particle physics. Keen to help out some with some basic homework questions and read more about people's experiences in the field of physics!
  26. Andrew Church

    I Composition of the Sun: How We Know via Spectral Absorption Lines

    The question “how do we know the composition of the sun” falls shorts everywhere I look. 1. There is the spectral absorption lines. Explanations given how that works, indicate how we know the elements, but fails to tell us how we know about the preponderance of Hydrogen and Helium...
  27. starstruck_

    Programs Still confused: Physics or Astronomy?

    Hey everyone! In a dilemma again, oops. I'm in the physics and astronomy program in university - going into my second year. I've completed courses for Astronomy and Physics in first year (same courses except astronomy has an extra - astronomy- course). Now that I'm selecting courses for second...
  28. GabrielLight

    I About gravitational binding energy and kinetic energy

    If a celestial body's kinetic energy (say, the Moon's) surpassed the energy necessary to exceed the gravitational binding energy (GBE), would said body break apart because of it? For example, the Moon is currently orbiting the Earth at a speed of 1020 meters per second, giving it a kinetic...
  29. Merlin3189

    Iridium flares end with replacement satellites

    For a long time I'd heard about Iridium flares, but not taken much trouble to see one. This week I took advantage of the uncommon spell of clear nights to pop out and look at a couple. Not quite what I'd expected, so I went to look into them a little more. One of the things I discovered is...
  30. P

    What was the rotational velocity of Earth on Dec 31, 1899

    I ask because time is defined with reference to this day (the SI second is based on a caesium clock is calibrated with reference to the 1952 ephemeris time standard, which was based on a second being 1/86 400th of Jan 0, 1900 (with Jan 0 being Dec 31 of 1899). So... how do I calculate the...
  31. P

    I How many degrees / radians is one full orbit of the Earth?

    One day consists of slightly more than 360° of rotation (360.9856°) on it's axis (due to Earth's orbit around the Sun). I imagine that one orbit is also either > or < 360° around the sun, relative to the motion of the sun around some object. Is this true, or is the orbit of the Earth...
  32. Sophrosyne

    B Spectroscopy of Stars: Electrons in Plasma

    Astronomers can determine the presence various elements in a star through spectroscopy of the incoming light from that star. The characteristic spectral lines of each element are formed by electrons transitioning between the various orbital energy levels around the nucleus of their atom. But...
  33. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 1: Introduction

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 1: Introduction

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  34. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 2: Kepler's Law

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 2: Kepler's Law

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  35. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 3: The Solar System

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 3: The Solar System

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  36. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 4: The Solar System (Contd.)

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 4: The Solar System (Contd.)

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  37. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 5: Binary Systems

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 5: Binary Systems

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  38. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 6: Binary Systems (Contd.)

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 6: Binary Systems (Contd.)

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  39. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 7: Tidal Forces and the Earth Moon System

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 7: Tidal Forces and the Earth Moon System

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  40. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 8: Fluid Mechanics

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 8: Fluid Mechanics

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  41. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 9: Hydrostatics and the Solar Wind

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 9: Hydrostatics and the Solar Wind

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  42. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 10: Radiative Transfer

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 10: Radiative Transfer

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  43. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 11: Radiative Transfer (Contd.)

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 11: Radiative Transfer (Contd.)

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  44. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 12: Thermal Radiation

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 12: Thermal Radiation

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  45. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 13: Thermal Radiation and the Sun

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 13: Thermal Radiation and the Sun

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  46. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 14: Virial Theorem and Its Application to Stars

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 14: Virial Theorem and Its Application to Stars

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  47. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 15: Stars: Magnitudes and the H-R Diagram

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 15: Stars: Magnitudes and the H-R Diagram

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  48. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 16: Stellar Physics - I

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 16: Stellar Physics - I

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  49. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 17:  Stellar Physics - II

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 17: Stellar Physics - II

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
  50. Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 18: Stellar Physics - III

    Astrophysics & Cosmology by Prof. S. Bharadwaj (NPTEL):- Lecture 18: Stellar Physics - III

    Copyright reserved to Prof. Bharadwaj and NPTEL, Govt. of India. Lectures: http://www.nptel.ac.in/courses/115105046/ Syllabus: http://www.nptel.ac.in/syllabus/syllabus.php?subjectId=115105046
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