Milky way Definition and 113 Discussions

The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλακτικός κύκλος (galaktikos kýklos, "milky circle"). From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.
The Milky Way is a barred spiral galaxy with an estimated visible diameter of 100,000–200,000 light-years. Recent simulations suggest that a dark matter disk, also containing some visible stars, may extend up to a diameter of almost 2 million light-years. The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, which is itself a component of the Laniakea Supercluster.It is estimated to contain 100–400 billion stars and at least that number of planets. The Solar System is located at a radius of about 27,000 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust. The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The galactic center is an intense radio source known as Sagittarius A*, a supermassive black hole of 4.100 (± 0.034) million solar masses. Stars and gases at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much (about 90%) of the mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed "dark matter". The rotational period is about 240 million years at the radius of the Sun. The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest stars in the Milky Way are nearly as old as the Universe itself and thus probably formed shortly after the Dark Ages of the Big Bang.

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  1. C

    B Milky Way is "in the top percentile of all the galaxies that exist"

    Our Galaxy is far bigger, brighter, and more massive than most others: Knowable Magazine Check out the amazing video, which shows all the many--more than 50!--satellite galaxies of the Milky Way burst into existence as they are discovered, year after year.
  2. newrd

    B Andromeda Collision VS Expansion

    Hi Folks, I've read that by the time mankind is ready for intergalactic travel, our nearest galactic neighbour will be too far to even travel to. But I've also read that Andromeda is on a collision course with the Milky Way. Which is correct? And if the universe is expanding and everything is...
  3. Sasho Andonov

    I Collision of Milky Way and Andromeda....?

    I do not understand how (in few bilion years) Milky Way and Andromeda will collide? If the universe is expanding and these objects which are far away have bigger speeds than those who are closer, than Milky Way and Andromeda will just be far away every moment... (?) Could someone help? :-)
  4. Suyash Singh

    Width of milky way

    I was wondering that we always see the diameter of milky way but no one talks about its width. Even on google it is not there. This means that if I go up instead of forward then I would be out of milky in an instant?
  5. C

    I How Bright Would the Milky Way Look If It Had No Dust?

    Interstellar dust prevents us from seeing most of the light of the Milky Way. Does anyone know how bright it would look if it had no dust at all? As it is, the Milky Way is impossible to see from cities and many suburbs, but how would the situation improve if there were no dust between the stars?
  6. S

    I Actual number of stars in the Milky Way

    I hear wild varying estimates of how many stars there are in the Milky Way Galaxy, from 200 billion to 400 billion. Is the number closer to 200 billion or closer to 400 billion? What methods are being employed (other than GAIA) in order to count them?
  7. D

    Is the Parenago Discontinuity a real thing?

    Recently I came across a discussion on a Pantheist forum concerning the movement of cooler Stars & the Parenago Discontinuity. The proposal was that this disconinuity could be used as a way of testing whether cooler Star have self determination... yeah yeah I know, I'm not asking here for a...
  8. S

    I Do stars have any lower mass limit?

    Just read an article about a discovery of the smallest/least massive star in the Milky Way galaxy. The star has 85 times the mass of Jupiter and is known as EBLM J0555-57Ab located about 600 light-years from Earth. The entire article here -...
  9. TreeLover

    B An exercise related to the mass of the Milky Way, sort of.

    So, in preparation to the Portuguese Astronomy Olympiads, I've stumbled upon this problem (exercise): The sun, which is 8 kpc away from the centre of the Milky Way, has a rotation speed of approximately 220 kms-1 . Whereas a a star that is 15 kpc from the centre of the Galaxy orbits at a speed...
  10. Shellsunde

    I Dipole repeller - what is it?

    Recently, I read a few popularized articles portraying a study and associated calculations using astronomical measurements that posits a characterization of the direction and acceleration (or velocity) of our galaxy. The researchers assert not only is our galaxy being attracted by massive...
  11. J

    B Why the Milky Way shows band in all-sky energy scans

    I have just read about the Gleamoscope which allows users to dial up visions of the sky in any light that you prefer, for example CMB, Xray, etc. In all of these, the Milky Way shows up as a narrow horizontal band across the middle of theall-sky image. What is it in the analysis that leads to...
  12. F

    I Orientation of the Earth, Sun and Solar System in the Milky Way

    I've been tinkering with a few diagrams in an attempt to illustrate the motion of the solar system in its journey around the Milky Way. I also wanted portray how the celestial, ecliptic and galactic coordinate systems are related to each other in a single picture. Note: in the Celestial, or...
  13. C

    B Found: The Least Luminous Galaxy Ever Seen

    Lying 280,000 light-years from Earth, the Virgo I galaxy emits only 180 times as much light as the Sun, half as much as the previous faint-galaxy champ. The galaxy's proximity to the Milky Way suggests that our Galaxy has hundreds of other satellite galaxies. New Scientist has the exclusive...
  14. Borg

    Stargazing GAIA - 1 billion stars and counting

    The GAIA telescope has been mapping stars in the Milky Way with unprecedented quality and quantities. It has been assembling the most detailed 3D map ever made of our Milky Way galaxy and has currently mapped over 1 billion stars. There are already hints that the Milky Way may be shaped...
  15. C

    B The Milky Way's Dark Twin Revealed

    A galaxy as massive as the Milky Way emits only 1% as much light. Link: Nature.
  16. Erenjaeger

    I Rate of supernovae

    Which option is closest to scientists' current best estimate for the rate at which a supernova explosions occur somewhere in the milky way galaxy? a) once a day b) once a year c) once every hundred years d) once every thousand years From what I have found online, the current estimate is one...
  17. C

    B New Galaxy is Largest Found Orbiting Milky Way in 20+ Years

    The Milky Way now has 49 known satellite galaxies, and the new one is the fourth largest. Link: New Scientist
  18. Stephanus

    Orbits in the universe

    Dear PF Forum, Lunar Satelite orbits the moon, The moon orbits the earth, The Earth orbits the sun, I know that some of you know about this picture You might want to tell me. "No Steven, the Sun also orbits the earth" But for all practical purpose, we'd say that the earth orbits the sun. So...
  19. C

    Hubble Finds Origin of Huge Cloud Crashing into our Galaxy

    In 2008, astronomers discovered that a multi-million-solar-mass cloud named Smith's Cloud would hit the Milky Way's disk in about 27 million years. Now new Hubble observations have identified the mysterious cloud's likely origin. Link: New Scientist
  20. C

    Milky Way stole its farthest star cluster from another galaxy

    by Ken Croswell Call it the case of the purloined star cluster. Observations reveal that our galaxy stole a distant globular star cluster from one of its neighbours. Link: New Scientist
  21. SheriffPeabody

    Gravitational lensing as a way of observing Milky Way?

    Hi Everyone, first post here, another enthusiastic amateur I'm afraid so please excuse my general ignorance! I struck me the other day that it should be possible to find an arrangement of large galaxies that would allow light emitting from our galaxy to be bent back towards us. This would give...
  22. ViperSRT3g

    Milky Way's Mass

    I just read this article on, and am now looking for any further insight into this. The article claims that the milky way may have approximately 210 billion solar masses of matter within 60,000 ly of the galactic center. If this is true, wouldn't that make the milky way nearly twice the...
  23. T

    Milky way jets

    Milky Way core drives wind at 2 million miles per hour -- ScienceDaily The article graphic shows three distinct flows of material... One moving towards earth One moving away from earth And One with no net motion along the line of...
  24. S

    Seeing the milky way in it's past

    Alright, this has been egging me for awhile now, so here it goes. If light has a finite speed, and the rate of acceleration of the expansion of the universe has sped inflation up past this finite speed, is it possible that one of the young galactic cores we observed through the deep field image...
  25. C

    Galaxy Wavelength (Milky Way)

    I am creating this wavelength chart (attached). I was told to use Compton's formula; I got this: (6.626068 × (10^(-34))) / (1.1542e+42 * 299 792 458) = 1.91493535 × 10-84 Apparently, it is substantially off scale. I was then told to try de Broglie wave. Wikipedia only shows relations...
  26. T

    THE CENTER of The Milky Way Galaxy

    THE CENTER of The Milky Way Galaxy! Supposedly, in the center of our galaxy (and in most galaxies, if I'm not mistaken) there is a super massive black hole. In my mind I've always had the picture of a galaxy where there is a bright light in the center and lots of starts orbiting it... so if...
  27. V

    Theoretical Question about Milky Way

    This may be a stupid question, but it just popped up in my mind a few minutes ago. Considering we are able to "look back in time" so to speak, because light takes so long to get here, is it possible for us to look in the night sky and see light that came from the Milky Way? Considering the...
  28. M

    Radio Noise from the Milky Way

    First of all, new to the forums, so HELLO! I am currently working on a project and cannot catch a break on what I need to be looking for. The project consists of calibrating antennas based on the radio noise from the Milky Way. We would like to point the antenna at the center of the milky way...
  29. D

    Density of dark matter in milky way

    Does anyone happen to know the average density of dark matter per unit volume in the milky way? I've seen at least one formula, but I'm not sure I fully comprehend it. Here is the equation I found: ρ0 = 4.5 × 10−2(r0/kpc) − (2/3)2x10^30kg pc−3 The only part of this equation that I can't...
  30. W

    Are LMC, SMC approaching the Milky Way ?

    Are LMC, SMC approaching the Milky Way ?? Are the LMC & SMC approaching towards, or receding from, the MWG ? According to my calculations, using the data from here, and accounting for a ~220 km / sec velocity of the Sun, towards galactic longitude b=90 degrees, the LMC is moving nearly...
  31. C

    Milky way gets a makeover

    Spiral galaxies are among the most beautiful and familiar objects in the heavens, but a working explanation as to why galaxies evolve into spirals has eluded astronomers for decades. Now, two independent researchers have published a compelling solution to this eighty year old problem, which...
  32. D

    Milky Way excess Microwave Radiation

    Could some of the cosmic background radiation be produced within the fabric of space itself? What if the big bang was not a one of event 15billion years ago but is happening right now today, now, all around us within the quantum world? If indeed the CBr was occurring within the fabric of...
  33. S

    How do you see the Milky Way?

    How do you see the whole of milky way if we are in it?
  34. G

    Question about our solar systems orbital path through the milky way

    Hello everyone this is my first time posting on this website. I wanted to know if our solar system takes a path through the milky way on a linear plane or if it garbages up and down on an unstable x and y path? Just so you all know I'm not an expert in theories or have any type of degree in...
  35. R

    The gravitational binding energy of the Milky Way?

    Does this even make sense? Just how immense would that be?
  36. Astronuc

    Large Gas Cloud near Aquila Rift in Milky Way

    Cosmic Cloud Poised to Birth Massive Star Ref: [Broken] A sleeping giant
  37. Y

    Photos of the our milky way galaxy

    I have seen several photos of the our milky way galaxy, other galaxies and some photos of even 100's of galaxies in the same picture. How do they do it? Usually if you see in the sky, all you see is the stars. (naked eyes) I believe to be able to see actual of our milky way galaxy we need to...
  38. S

    Is It Possible To View The Milky Way In The UK

    Is It Possible To View The Milky Way In The UK, during the UK summer time months, i have just moved here and i was wondering whether i can see the milky way on a clear summer night, the shot I am looking for is something like this...
  39. W

    Stellar orbits around the milky way.

    I was just thinking about how this is done. I have looked online and I can't find a none mathematical explanation. If I am getting it right, we get the orbits by measuring the radial and tangential velocities of several stars relative to our sun. I thought the tangential velocity was...
  40. H

    What I see in sky - Milky Way, other stars

    I've wondered about this for a while: -the Milky Way which we are part of appears to be a white cloudish streak in the sky. I guess this is because the stars are so far away that it appears as a cloud of light? -But I would assume that all the stars in the Milky Way, our own galazy, must...
  41. C

    What is our Solar System's orbital plane around the Milky Way?

    Does anyone know a good link to an animation or nice diagram showing how our solar system orbits the center of our milky way? I always imagined the milky way's plane, where most of the material is accumulated, as a record, granted, with a bigger bulge and 2/3 out from the center of that record...
  42. Redbelly98

    Milky Way spins faster, has more mass than thought

    Saw this on Yahoo! News; the title pretty much sums it up. [Broken] My question for the regular astro PFers: what would be the sun's revolution period around the galaxy based on this new information?
  43. D

    Traversing the milky way galaxy! when?

    Traversing the milky way galaxy! when? Traversing our own galaxy is a lifelong quest for me and I am actually pondering it and long for it all the time, except when I am sleeping. Maybe it's just a fantasy, though I am not into science-fiction version of it, but many of us want to eventually...
  44. S

    The Milky Way is twice the size we thought it was

    It took just a couple of hours using data available on the internet for University of Sydney scientists to discover that the Milky Way is twice as wide as previously thought. Astrophysicist Professor Bryan Gaensler led a team that has found that our galaxy - a flattened spiral about 100,000...
  45. P

    The ecliptic planes of the Milky Way and the solar system

    Our Milky Way is a spiral galaxy whose ecliptic plane is the same with the ecliptic of the Sun (or nearly). So do you think all other solar systems in the Milky Way also have the same characteristics?
  46. Holocene

    Typical stellar distances of visible stars in the Milky Way

    How far away is the average star in the night sky? I mean, can we see stars that are on the other side of the galaxy? Perhaps most of the visible stars are maybe just a few dozen light years away?
  47. jal

    WMAP tend to coincide with radio emissions from the Milky Way

    Have these papers been discused. High Galactic Latitude Interstellar Neutral Hydrogen Structure and Associated (WMAP) High Frequency Continuum Emission Authors: Gerrit L. Verschuur (Submitted on 9 Apr 2007 (v1), last revised 23 Jul 2007 (this version, v2))...
  48. Loren Booda

    More stars in the Milky Way or galaxies in the universe?

    Do you think there are more stars in our Milky Way galaxy, or galaxies in the observable universe?
  49. PhanthomJay

    View of Milky Way from Earth

    When we view the Milky Way with the naked eye from Earth in the winter night sky, we see the streakish 'cloud' of its spiral arms. Are we looking in toward its center toward the inner arms, or out toward its outer arms? And vice versa in summer? I don't recall ever noticing any difference in the...
  50. R

    Orbits of Andromeda and Milky Way Galaxy About Each Other

    The orbits of the Magellanic Clouds about the Milky Way Galaxy have apparently been determined, and the two dwarf irregular galaxies are now about as close as they will get to the MW in their 2.2 billion year orbit. See p. 42 of "Our Growing, Breathing Galaxy" by Wakker and Richter, Scientific...