NASA astronaut Greg Chamitoff during a 2011 spacewalk on the International Space Station. Reflected in his visor is NASA crewmate Mike Fincke. Both astronauts were mission specialists aboard shuttle mission STS-134. Credit: NASA
Spacewalks have been described by astronauts as magical, amazing, and “holy moly!” This new 30-minute NASA documentary called “Suit Up!” celebrates 50 years of extravehicular activity (EVA) or spacewalks. 50 years ago this year, the first spacewalks were conducted by Russian Alexei Leonov in March 1965 and then American astronaut Edward White followed soon after in June 1965. The documentary features interviews with astronauts past and present, as well as other astronauts, engineers, technicians, managers from the history of spacewalks.
They share their personal stories and thoughts that cover the full EVA experience — from the early spacewalking experiences, to spacesuit manufacturing, to modern day spacewalks aboard the International Space Station as well as what the future holds for humans working on a tether in space.
“Suit Up,” is narrated by actor and fan of space exploration Jon Cryer.
Nuclear physicist Enrico Fermi won the 1938 Nobel Prize for a technique he developed to probe the atomic nucleus. He led the team that developed the world's first nuclear reactor, and played a central role in the Manhattan Project that developed the atomic bomb during World War II. In the debate over extraterrestrial intelligence, he is best known for posing the question 'Where is everybody?' during a lunchtime discussion at Los Alamos National Laboratory. His question was seen as the basis for the "Fermi Paradox". Credit: Smithsonian Institution Archives.
Welcome back to our Fermi Paradox series, where we take a look at possible resolutions to Enrico Fermi’s famous question, “Where Is Everybody?” Today, we examine the lunchtime conversation that started it all!
It’s become a kind of legend, like Newton and the apple or George Washington and the cherry tree. One day in 1950, the great physicist Enrico Fermi sat down to lunch with colleagues at the Fuller Lodge at Los Alamos National Laboratory in New Mexico and came up with a powerful argument about the existence of extraterrestrial intelligence, the so-called “Fermi paradox”.
But like many legends, it’s only partly true. Robert Gray explained the real history in a recent paper in the journal Astrobiology. Enrico Fermi was the winner of the 1938 Nobel Prize for physics, led the team that developed the world’s first nuclear reactor at the University of Chicago, and was a key contributor to the Manhattan Project that developed the atomic bomb during World War II. The Los Alamos Lab where he worked was founded as the headquarters of that project.
Alexei Leonov during the first ever spacewalk on March 18, 1965. 3-D anaglyph created from individual frames from the movie of the walk by Andrew Chaikin.
On March 18, 1965 Soviet cosmonaut Alexei Leonov made the first spacewalk in history, floating outside his Voskhod 2 capsule. Leonov made the walk when he was just 30 years old, and later wrote that he felt “like a seagull with its wings outstretched, soaring high above the Earth.” His spacewalk lasted just 12 minutes but that was long enough to prove that humans in space could work outside a spacecraft.
Author and space historian Andrew Chaikin created some unique 3-D views of Leonov’s spacewalk, made from individual frames from the movie of the walk. Above is a red-cyan anaglyph, but if you don’t have your 3-D glasses available, don’t worry: Chaikin has also created stereo pair 3-D images, which you can view by crossing your eyes (explanation below, if you need a little help).
Alexei Leonov during the first ever spacewalk on March 18, 1965. Cross-eyed 3-D stereo pair created from individual frames from the movie of the walk. Credit: Andrew Chaikin.
Oxford University provides this explanation of how to cross your eyes to view a stereo pair as a 3-D image:
Hold a finger a short distance in front of your eyes and stare at it. In the background you should see two copies of the stereo pair, giving four views altogether. Move your finger away from you until you see the middle two of the four images come together. You should now see just three images in the background. Try to direct your attention slowly toward the middle image without moving your eyes, and it should gradually come into focus.
Alexei Leonov during the first ever spacewalk on March 18, 1965. 3-D anaglyph created from individual frames from the movie of the walk. Credit: Andrew Chaikin.
While the spacewalk was exhilarating, getting back into the spacecraft became dicey. Leonov’s spacesuit expanded so much in the vacuum of space that he had a hard time squeezing back into the spacecraft. He took a risk and opened a valve on the suit to let enough air escape, which allowed him to enter the airlock.
Leonov’s walk took place almost 3 months before American astronaut Ed White took his spacewalk on Gemini 4. The first European to do a spacewalk was the French spationaute Jean-Loup Chrétien, who flew to the Russian Mir space station in 1988.
Alexei Leonov during the first ever spacewalk on March 18, 1965. Cross-eyed 3-D stereo pair created from individual frames from the movie of the walk. Credit: Andrew Chaikin.
Alexei Leonov during the first ever spacewalk on March 18, 1965. 3-D anaglyph created from individual frames from the movie of the walk. Credit: Andrew Chaikin.
Alexei Leonov during the first ever spacewalk on March 18, 1965. Cross-eyed 3-D stereo pair created from individual frames from the movie of the walk. Credit: Andrew Chaikin.
Thanks to Andrew Chaikin for sharing these images with Universe Today.
Group photo of the first cosmonauts. Taken just after the flight of Voskhod 2 in 1965, in order of flight (from left), the first Soviet cosmonauts: Yuri Gagarin, Gherman Titov, Andrian Nikolayev, Pavel Popovich, Valeri Bykovsky, Valentina Tereshkova, Konstantin Feoktistov, Vladimir Komarov, Boris Yegorov, Pavel Belyayev and Alexei Leonov. Alexei had just returned to Earth after performing the first spacewalk in history during the Voskhod 2 mission. Credit: alldayru.com, via ESA.
The Sun provides energy for life here on Earth through light and heat. Credit: NASA Goddard Space Flight Center
How far is the Sun? It seems as if one could hardly ask a more straightforward question. Yet this very inquiry bedeviled astronomers for more than two thousand years.
Certainly it’s a question of nearly unrivaled importance, overshadowed in history perhaps only by the search for the size and mass of the Earth. Known today as the astronomical unit, the distance serves as our reference within the solar system and the baseline for measuring all distances in the Universe.
Thinkers in Ancient Greece were among the first to try and construct a comprehensive model of the cosmos. With nothing but naked-eye observations, a few things could be worked out. The Moon loomed large in the sky so it was probably pretty close. Solar eclipses revealed that the Moon and Sun were almost exactly the same angular size, but the Sun was so much brighter that perhaps it was larger but farther away (this coincidence regarding the apparent size of the Sun and Moon has been of almost indescribable importance in advancing astronomy). The rest of the planets appeared no larger than the stars, yet seemed to move more rapidly; they were likely at some intermediate distance. But, could we do any better than these vague descriptions? With the invention of geometry, the answer became a resounding yes. Continue reading “How Did We Find the Distance to the Sun?”
An example of a telescope logbook waiting to be transcribed. Credit: Smithsonian
An old brick building on Harvard’s Observatory Hill is overflowing with rows of dark green cabinets — each one filled to the brim with hundreds of astronomical glass plates in paper sleeves: old-fashioned photographic negatives of the night sky.
All in all there are more than 500,000 plates preserving roughly a century of information about faint happenings across the celestial sphere. But they’re gathering dust. So the Harvard College Observatory is digitizing its famed collection of glass plates. One by one, each plate is placed on a scanner capable of measuring the position of each tiny speck to within 11 microns. The finished produce will lead to one million gigabytes of data.
But each plate must be linked to a telescope logbook — handwritten entries recording details like the date, time, exposure length, and location in the sky. Now, Harvard is seeking your help to transcribe these logbooks.
The initial project is called Digital Access to a Sky Century at Harvard (DASCH). Although it has been hard at work scanning roughly 400 plates per day, without the logbook entries to accompany each digitized plate, information about the brightness and position of each object would be lost. Whereas with that information it will be possible to see a 100-year light curve of any bright object within 15 degrees of the north galactic pole.
The century of data allows astronomers to detect slow variations over decades, something otherwise impossible in today’s recent digital era.
Assistant Curator David Sliski is especially excited about the potential overlap in our hunt for exoplanets. “It covers the Kepler field beautifully,” Sliski told Universe Today. It should also be completed by the time next-generation exoplanet missions (such as TESS, PLATO, and Kepler 2) come online — allowing astronomers to look for long-term variability in a host star that may potentially affect an exoplanet’s habitability.
There are more than 100 logbooks containing about 100,000 pages of text. Volunteers will type in a few numbers per line of text onto web-based forms. It’s a task impossible for any scanner since optical character recognition doesn’t work on these hand-written entries.
Harvard is partnering with the Smithsonian Transcription Center to recruit digital volunteers. The two will then be able to bring the historic documents to a new, global audience via the web. To participate in this new initiative, visit Smithsonian’s transcription site here.
The Saturn V rocket bearing Apollo 11 lifts off from the Kennedy Space Center on July 20, 1969. Credit: NASA
45 years ago today — on July 16th, 1969 — the Apollo 11 crew left Earth for the first human mission to land on the Moon. Launching on at Saturn V rocket from Cape Kennedy, the mission sent Commander Neil Armstrong, Command Module Pilot Michael Collins and Lunar Module Pilot Edwin “Buzz” Aldrin into an initial Earth-orbit, and then two hours and 44 minutes after launch, another burn of the engines put Apollo 11 into a translunar orbit.
If you want to re-live the launch and the mission, there are several ways you can participate. We’ve included here a few different replays of the launch, varying from a quick recap to a detailed look at the launch itself. Above is the newscast of the launch from CBS news with Walter Cronkite, and we’ve got more below.
Also below is information on several webcasts and other events that NASA has planned to commemorate the anniversary.
Here’s a detailed look at the launch in ultra-slow motion, with narration:
Here is some remastered high definition footage from NASA of the Apollo 11 launch, but there’s no audio.
And here’s a quick look at the entire Apollo 11 mission, all in just 100 seconds from Spacecraft Films:
Here are some ways to participate in the anniversary:
On Twitter, @ReliveApollo11 from the Smithsonian National Air and Space Museum is reliving the highlights from Apollo 11 mission to the Moon in “real time” 45 years later.
Also @NASAHistory is tweeting images and events from the mission, and journalist Amy Shira Teitel (@astVintageSpace ) is tweeting out some interesting pictures, facts and quotes from the mission, in “real time” (again 45 years later).
To join the ongoing conversation on social media about the anniversary and NASA’s deep space exploration plans, use the hashtags #NextGiantLeap and #Apollo45.
On Friday, July 18 at 10:30 a.m. PDT (1:30 p.m. EDT), NASA TV will air a live conversation about the future of space exploration with actor, director and narrator Morgan Freeman. He will speak at NASA’s Jet Propulsion Laboratory in Pasadena, California, about his personal vision for space. The event also will include NASA astronaut Reid Wiseman participating from the International Space Station.
Also on Friday at 3:30 p.m. EDT, NASA will host a discussion with Buzz Aldrin and astronaut Mike Massimino at the Intrepid Sea, Air & Space Museum in New York during the Intrepid Space and Science Festival. NASA also will have exhibits and activities at the festival Thursday, July 17 through Saturday, July 19. There’s more information about the festival here.
On Sunday, July 20 at 7:39 p.m. PDT (10:39 p.m. EDT), when Armstrong opened the spacecraft hatch to begin the first spacewalk on the moon, NASA TV will replay the restored footage of Armstrong and Aldrin’s historic steps on the lunar surface.
On Monday, July 21 at 7 a.m. PDT (10 a.m. EDT) from the agency’s Kennedy Space Center in Florida, NASA TV will air live coverage of the renaming of the center’s Operations and Checkout Building in honor of Armstrong, who passed away in 2012. The renaming ceremony will include NASA Administrator Charles Bolden, Kennedy Center Director Robert Cabana, Apollo 11’s Collins, Aldrin and astronaut Jim Lovell, who was the mission’s back-up commander. International Space Station NASA astronauts Wiseman and Steve Swanson, who is the current station commander, also will take part in the ceremony from their orbiting laboratory 260 miles above Earth.
Kennedy’s Operations and Checkout Building has played a vital role in NASA’s spaceflight history. It was used during the Apollo program to process and test the command, service and lunar modules. Today, the facility is being used to process and assemble NASA’s Orion spacecraft, which the agency will use to send astronauts to an asteroid in the 2020s and Mars in the 2030s.
On Thursday, July 24 at 3 p.m. PDT (6 p.m. EDT), which is the 45th anniversary of Apollo 11’s return to Earth, the agency will host a panel discussion — called NASA’s Next Giant Leap — from Comic-Con International in San Diego. Moderated by actor Seth Green, the panel includes Aldrin, NASA Planetary Science Division Director Jim Green, JPL systems engineer Bobak Ferdowsi, and NASA astronaut Mike Fincke, who will talk about Orion and the Space Launch System rocket, which will carry humans on America’s next great adventure in space.
The NASA.gov website will host features, videos, and historic images and audio clips that highlight the Apollo 11 anniversary, as well as the future of human spaceflight. Find it all here.
Also, the Slooh telescope team will celebrate the 45th anniversary of the Apollo 11 landing with a high-definition broadcast of the lunar surface on Sunday, July 20th starting at 5:30 PM PDT / 8:30 PM EDT / 00:30 UTC (7/21) – (check International Times here) Slooh will broadcast the event live from a special feed located in Dubai in the United Arab Emirates.
Viewers can watch the event unfold free on Slooh.com, or in the webcast below. The image stream will be accompanied by discussions led by Slooh host, Geoff Fox, Slooh astronomer, Bob Berman, Slooh Observatory Engineer, Paul Cox, along with numerous special guests, including documentary filmmaker, Duncan Copp, and science journalist, Andrew Chaikin. Viewers can follow updates on the show by using the hashtag #SloohApollo11.
Albert Einstein during a lecture in Vienna in 1921.
Credit: National Library of Austria/F Schmutzer/Public Domain
One of the benefits of being an astrophysicist is your weekly email from someone who claims to have “proven Einstein wrong”. These either contain no mathematical equations and use phrases such as “it is obvious that..”, or they are page after page of complex equations with dozens of scientific terms used in non-traditional ways. They all get deleted pretty quickly, not because astrophysicists are too indoctrinated in established theories, but because none of them acknowledge how theories get replaced.
For example, in the late 1700s there was a theory of heat known as caloric. The basic idea of caloric was that it was a fluid that existed within materials. This fluid was self-repellant, meaning it would try to spread out as evenly as possible. We couldn’t observe this fluid directly, but the more caloric a material has the greater its temperature.
Ice-calorimeter from Antoine Lavoisier’s 1789 Elements of Chemistry. (Public Domain)
From this theory you get several predictions that actually work. Since you can’t create or destroy caloric, heat (energy) is conserved. If you put a cold object next to a hot object, the caloric in the hot object will spread out to the cold object until they reach the same temperature. When air expands, the caloric is spread out more thinly, thus the temperature drops. When air is compressed there is more caloric per volume, and the temperature rises.
We now know there is no “heat fluid” known as caloric. Heat is a property of the motion (kinetic energy) of atoms or molecules in a material. So in physics we’ve dropped the caloric model in terms of kinetic theory. You could say we now know that the caloric model is completely wrong.
Except it isn’t. At least no more wrong than it ever was.
The basic assumption of a “heat fluid” doesn’t match reality, but the model makes predictions that are correct. In fact the caloric model works as well today as it did in the late 1700s. We don’t use it anymore because we have newer models that work better. Kinetic theory makes all the predictions caloric does and more. Kinetic theory even explains how the thermal energy of a material can be approximated as a fluid.
This is a key aspect of scientific theories. If you want to replace a robust scientific theory with a new one, the new theory must be able to do more than the old one. When you replace the old theory you now understand the limits of that theory and how to move beyond it.
In some cases even when an old theory is supplanted we continue to use it. Such an example can be seen in Newton’s law of gravity. When Newton proposed his theory of universal gravity in the 1600s, he described gravity as a force of attraction between all masses. This allowed for the correct prediction of the motion of the planets, the discovery of Neptune, the basic relation between a star’s mass and its temperature, and on and on. Newtonian gravity was and is a robust scientific theory.
Then in the early 1900s Einstein proposed a different model known as general relativity. The basic premise of this theory is that gravity is due to the curvature of space and time by masses. Even though Einstein’s gravity model is radically different from Newton’s, the mathematics of the theory shows that Newton’s equations are approximate solutions to Einstein’s equations. Everything Newton’s gravity predicts, Einstein’s does as well. But Einstein also allows us to correctly model black holes, the big bang, the precession of Mercury’s orbit, time dilation, and more, all of which have been experimentally validated.
So Einstein trumps Newton. But Einstein’s theory is much more difficult to work with than Newton’s, so often we just use Newton’s equations to calculate things. For example, the motion of satellites, or exoplanets. If we don’t need the precision of Einstein’s theory, we simply use Newton to get an answer that is “good enough.” We may have proven Newton’s theory “wrong”, but the theory is still as useful and accurate as it ever was.
Unfortunately, many budding Einsteins don’t understand this.
Binary waves from black holes. Image Credit: K. Thorne (Caltech) , T. Carnahan (NASA GSFC)
To begin with, Einstein’s gravity will never be proven wrong by a theory. It will be proven wrong by experimental evidence showing that the predictions of general relativity don’t work. Einstein’s theory didn’t supplant Newton’s until we had experimental evidence that agreed with Einstein and didn’t agree with Newton. So unless you have experimental evidence that clearly contradicts general relativity, claims of “disproving Einstein” will fall on deaf ears.
The other way to trump Einstein would be to develop a theory that clearly shows how Einstein’s theory is an approximation of your new theory, or how the experimental tests general relativity has passed are also passed by your theory. Ideally, your new theory will also make new predictions that can be tested in a reasonable way. If you can do that, and can present your ideas clearly, you will be listened to. String theory and entropic gravity are examples of models that try to do just that.
But even if someone succeeds in creating a theory better than Einstein’s (and someone almost certainly will), Einstein’s theory will still be as valid as it ever was. Einstein won’t have been proven wrong, we’ll simply understand the limits of his theory.
Before having to close the door (temporarily) today, NASA put together this nice graphic of the highlights of their accomplishments of the past 55 years, as well as what the hopes and plans are for the future.
The National Aeronautics and Space Administration began operating on October 1, 1958, managing the US’s burgeoning space exploration program. NASA replaced the National Advisory Committee for Aeronautics (NACA) agency, which began in 1915 to undertake and promote aeronautical research.
Now, NASA is in the midst of expanding commercial access to the International Space Station with the rendezvous of Orbital Science’s Cygnus capsule this week. While the ISS is still operating, and when full operations resume throughout NASA, they’ll continue work on exploring space, monitoring Earth, unlocking mysteries of our solar system and peering back into the beginnings of the Universe.
Our advice to you? If you are a US citizen, write your Congress-people and tell them how important you feel NASA is to the future of the nation and the world. And while you’re at it, tell them to get to work and do the job they were elected to do. Find out who represents you in the US Congress here.
Only two of three parachutes worked correctly for the return of Apollo 15. Credit: NASA.
On this day in history, the crew of Apollo 15 returned home from their mission to the Moon. But the splashdown in the Pacific Ocean wasn’t without a little drama. One of the three parachutes failed to open fully, but astronauts Dave Scott, Al Worden, and Jim Irwin didn’t know it until they were almost ready to hit the ocean.
“Apollo 15, this is Okinawa. You have a streamed chute. Stand by for a hard impact.”
The recovery ship, USS Okinawa radioed to the crew that one parachute was not inflated. Technically, the Apollo capsule really only needed two chutes to land, with the third being for redundancy, but still, the landing was harder than other Apollo missions. However, no damage or injury resulted.
Experts looking at this photo say that two or three of the six riser legs on the failed parachute were missing, and after looking into the issue, it was determined that excess fuel burning from the Command Module Reaction Control System likely caused the lines to break.
Apollo 15 landed about about 320 miles (515 kilometers) north of Hawaii.
“No scientific discovery is named after its discoverer,” – Stigler/Merton.
Edwin Hubble’s contributions to astronomy earned him the honor of having his name bestowed upon arguably the most famous space telescope (the Hubble Space Telescope, HST). Contributions that are often attributed to him include the discovery of the extragalactic scale (there exist countless other galaxies beyond the Milky Way), the expanding Universe (the Hubble constant), and a galaxy classification system (the Hubble Tuning Fork). However, certain astronomers are questioning Hubble’s pre-eminence in those topics, and if all the credit is warranted.
“[The above mentioned] discoveries … are well-known … and most astronomers would associate them solely with Edwin Hubble; yet this is a gross oversimplification. Astronomers and historians are beginning to revise that standard story and bring a more nuanced version to the public’s attention,” said NASA scientist Michael J. Way, who just published a new study entitled “Dismantling Hubble’s Legacy?”
Has history clouded our view of Hubble the man? Or are his contributions seminal to where we are today in astronomy?
Assigning credit for a discovery is not always straightforward, and Way 2013 notes, “How credit is awarded for a discovery is often a complex issue and should not be oversimplified – yet this happens time and again. Another well-known example in this field is the discovery of the Cosmic Microwave Background.” Indeed, controversy surrounds the discovery of the Universe’s accelerated expansion, which merely occurred in the late 1990s. Conversely, the discoveries attributed to Hubble transpired during the ~1920s.
The Hubble Space Telescope (image credit: NASA, tweaked by D. Majaess).
Prior to commencing this discussion, it’s emphasized that Hubble cannot defend his contribution since he died long ago (1889-1953). Moreover, we can certainly highlight the efforts of other individuals whose seminal contributions were overlooked without mitigating Hubble’s pertinence. The first topic discussed here is the discovery of the extragalactic scale. Prior to the 1920s it was unclear whether the Milky Way galaxy and the Universe were synonymous. In other words, was the Milky Way merely one among countless other galaxies?
Astronomers H. Shapley and H. Curtis argued the topic in the famed Island Universe debate (1920). Curtis believed in the extragalactic Universe, whereas Shapley took the opposing view (see also Trimble 1995 for a review). In the present author’s opinion, Hubble’s contributions helped end that debate a few years later and changed the course of astronomy, namely since he provided evidence of an extragalactic Universe using a distance indicator that was acknowledged as being reliable. Hubble used stars called Cepheid variables to help ascertain that M31 and NGC 6822 were more distant than the estimated size of the Milky Way, which in concert with their deduced size, implied they were galaxies. Incidentally, Hubble’s distances, and those of others, were not as reliable as believed (e.g., Fernie 1969, Peacock 2013). Peacock 2013 provides an interesting comparison between distance estimates cited by Hubble and Lundmark with present values, which reveals that both authors published distances that were flawed in some manner. Having said that, present-day estimates are themselves debated.
Hubble’s evidence helped convince even certain staunch opponents of the extragalactic interpretation such as Shapley, who upon receiving news from Hubble concerning his new findings remarked (1924), “Here is the letter that has destroyed my universe.” Way 2013 likewise notes that, “The issue [concerning the extragalactic scale] was effectively settled by two papers from Hubble in 1925 in which he derived distances from Cepheid variables found in M31 and M33 (Hubble 1925a) of 930,000 light years and in NGC 6822 (Hubble 1925c) of 700,000 light years.”
However, as table 1 from Way 2013 indicates (shown below), there were numerous astronomers who published distances that implied there were galaxies beyond the Milky Way. Astronomer Ian Steer, who helps maintain the NASA/IPAC Extragalactic Database of Redshift-Independent Distances (NED-D), has also compiled a list of 290 distances to galaxies published before 1930. Way 2013 added that, “Many important contributions to this story have been forgotten and most textbooks in astronomy today, if they discuss the “Island Universe” confirmation at all, bestow 100% of the credit on Hubble with scant attention to the earlier observations that clearly supported his measurements.”
Thus Hubble did not discover the extragalactic scale, but his work helped convince a broad array of astronomers of the Universe’s enormity. However, by comparison to present-day estimates, Hubble’s distances are too short owing partly to the existing Cepheid calibration he utilized (Fernie 1969, Peacock 2013 also notes that Hubble’s distances were flawed for other reasons). That offset permeated into certain determinations of the expansion rate of the Universe (the Hubble constant), making the estimate nearly an order of magnitude too large, and the implied age for the Universe too small.
Way 2013 notes, “Table 1 lists all of the main distance estimates to spiral nebulae (known to this author) from the late 1800s until 1930 when standard candles began to be found in spiral nebulae [galaxies].” (image credit: Way 2013/arXiv).Hubble’s accreditation as the discoverer of the expanding Universe (the Hubble constant) has generated considerable discussion, which is ultimately tied to the discovery of a relationship between a galaxy’s velocity and its distance. An accusation even surfaced that Hubble may have censored the publication of another scientist to retain his pre-eminence. That accusation has since been refuted, but provides the reader an indication of the tone of the debate (see Livio 2012 (Nature), and references therein).
Hubble published his findings on the velocity-distance relation in 1929, under the unambiguous title, “A Relation Between Distance and Radial Velocity Among Extra-Galactic Nebulae”. Hubble 1929 states at the outset that other investigations have sought, “a correlation between apparent radial velocities and distances, but so far the results have not been convincing.” The key word being convincing, clearly a subjective term, but which Hubble believes is the principal impetus behind his new effort. In Lundmark 1924, where a velocity versus distance diagram is plotted for galaxies (see below), that author remarks that, “Plotting the radial velocities against these relative distances, we find that there may be a relation between the two quantities, although not a very definite one.” However, Hubble 1929 also makes reference to a study by Lundmark 1925, where Lundmark underscores that, “A rather definite correlation is shown between apparent dimensions and radial velocity, in the sense that the smaller and presumably more distant spirals have the higher space velocity.”
Hubble 1929 provides a velocity-distance diagram (featured below) and also notes that, “the data indicate a linear correlation between distances and velocities”. However, Hubble 1929 explicitly cautioned that, “New data to be expected in the near future may modify the significance of the present investigation, or, if confirmatory, will lead to a solution having many times the weight. For this reason it is thought premature to discuss in detail the obvious consequences of the present results … the linear relation found in the present discussion is a first approximation representing a restricted range in distance.” Hubble implied that additional effort was required to acquire observational data and place the relation on firm (convincing) footing, which would appear in Hubble and Humason 1931. Perhaps that may partly explain, in concert with the natural tendency of most humans to desire recognition and fame, why Hubble subsequently tried to retain credit for the establishment of the velocity-distance relation.
Hubble 1929 conveyed that he was aware of prior (but unconvincing to him) investigations on the topic of the velocity-distance relation. That is further confirmed by van den Bergh 2011, who cites the following pertinent quote recounted by Hubble’s assistant (Humason) for an oral history project, “The velocity-distance relationship started after one of the IAU meetings, I think it was in Holland [1928]. And Dr. Hubble came home rather excited about the fact that two or three scientists over there, astronomers, had suggested that the fainter the nebulae were, the more distant they were and the larger the red shifts would be. And he talked to me and asked if I would try and check that out.”
The velocities of galaxies plotted as a function of their distance, from Lundmark 1924 (left) and Hubble 1929 (right). Note the separate scales on the x-axis. Peacock 2013 demonstrates that distances cited by both authors were ultimately flawed, and problems (albeit less acute) likewise exist with modern distances (image credit: Lundmark/MNRAS/Hubble/PNAS, assembled by D. Majaess).
Hubble 1929 elaborated that, “The outstanding feature, however, is the possibility that the velocity-distance relation may represent the de Sitter effect, and hence that numerical data may be introduced into discussions of the general curvature of space.” de Sitter had proposed a model for the Universe whereby light is redshifted as it travels further from the emitting source. Hubble suspected that perhaps his findings may represent the de Sitter effect, however, Way 2013 notes that, “Thus far historians have unearthed no evidence that Hubble was searching for the clues to an expanding universe when he published his 1929 paper (Hubble 1929b).” Indeed, nearly two decades after the 1929 publication, Hubble 1947 remarks that better data may indicate that, “redshifts may not be due to an expanding universe, and much of the current speculation on the structure of the universe may require re-examination.” It is thus somewhat of a paradox that, in tandem with the other reasons outlined, Hubble is credited with discovering that the Universe is expanding.
The term redshift stems from the fact that when astronomers (e.g., V. Slipher) examined the spectra of certain galaxies, they noticed that although a particular spectral line should have appeared in the blue region of the spectrum (as measured in a laboratory): the line was actually shifted redward. Hubble 1947 explained that, “light-waves from distant nebulae [galaxies] seem to grow longer in proportion to the distance they have travelled It is as though the stations on your radio dial were all shifted toward the longer wavelengths in proportion to the distances of the stations. In the nebular [galaxy] spectra the stations (or lines) are shifted toward the red, and these redshifts vary directly with distance–an approximately linear relation. This interpretation lends itself directly to theories of an expanding universe. The interpretation is not universally accepted, but even the most cautious of us admit that redshifts are evidence either of an expanding universe or of some hitherto unknown principle of nature.”
Top, spectra for galaxies that are redshifted (image credit: JPL/Caltech/Planck).
As noted above, Hubble was not the first to deduce a velocity-distance relation for galaxies, and Way 2013 notes that, “Lundmark (1924b): first distance vs. velocity plot for spiral nebulae [galaxies] …Georges Lemaitre (1927): derived a non–static solution to Einstein’s equations and coupled it to observations to reveal a linear distance vs. redshift relation with a slope of 670 or 575 km/s/Mpc (depending on how the data is grouped) …” Although Hubble was aware of Lundmark’s research, he and numerous other astronomers were likely unaware of the now famous 1927 Lemaitre study, which was published in an obscure journal (see Livio 2012 (Nature), and discussion therein). Steer 2013 notes that, “Lundmark’s [1924] distance estimates were consistent with a Hubble constant of 75 km/s/Mpc [which is close to recent estimates].” (see also the interpretation of Peacock 2013). Certain distances established by Lundmark appear close to present determinations (e.g., M31, see the table above).
So why was Hubble credited with discovering the expanding Universe? Way 2013 suggests that, “Hubble’s success in gaining credit for his … linear distance-velocity relation may be related to his verification of the Island Universe hypothesis –after the latter, his prominence as a major player in astronomy was affirmed. As pointed out by Merton (1968) credit for simultaneous (or nearly so) discoveries is usually given to eminent scientists over lesser-known ones.” Steer told Universe Today that, “Lundmark in his own words did not find a definite relation between redshift and distance, and there is no linear relation overplotted in his redshift-distance graph. Where Lundmark used a single unproven distance indicator (galaxy diameters), cross-checked by a single unproven distance to the Andromeda galaxy, Hubble used multiple indicators including one still in use (brightest stars), cross-checked with distances to multiple galaxies based on Cepheids variables stars.”
Concerning assigning credit for the discovery of the expansion of the Universe, Way 2013 concludes that, “Overall we find that Lemaitre was the first to seek and find a linear relation between distance and velocity in the context of an expanding universe, but that a number of other actors (e.g. Carl Wirtz, Ludwik Silberstein, Knut Lundmark, Edwin Hubble, Willem de Sitter) were looking for a relation that fit into the context of de Sitter’s [Universe] Model B world with its spurious radial velocities [the redshift].” A partial list of the various contributors highlighted by van den Bergh 2011 is provided below.
“The history of the discovery of the expansion of the Universe may be summarized [above],” van den Bergh 2011 (image credit: van den Bergh/JRASC/arXiv).Way and Nussbaumer 2011 assert that, “It is still widely held that in 1929 Edwin Hubble discovered the expanding Universe … that is incorrect. There is little excuse for this, since there exists sufficient well-supported evidence about the circumstances of the discovery.”
In sum, the author’s personal opinion is that Hubble’s contributions to astronomy were seminal. Hubble helped convince astronomers of the extragalactic distance scale and that a relationship existed between the distance to a galaxy and its velocity, thus propelling the field and science forward. His extragalactic distances, albeit flawed, were also used to draw important conclusions (e.g., by Lemaitre 1927). However, it is likewise clear that other individuals are meritorious and deserve significant praise. The contributions of those scientists should be highlighted in parallel to Hubble’s research, and astronomy textbooks should be revised to emphasize those achievements A fuller account should be cited of the admirable achievements made by numerous astronomers working in synergy during the 1920s.
There are a diverse set of opinions on the topics discussed, and the reader should remain skeptical (of the present article and other interpretations), particularly since knowledge of the topic is evolving and more is yet to emerge. Two talks from the “Origins of the Expanding Universe: 1912-1932” conference are posted below (by H. Nussbaumer and M. Way), in addition to a talk by I. Steer from a separate event.
!["The history of the discovery of the expansion of the Universe may be summarized [above]", S. van den Bergh 2011. Image credit: S. van den Bergh/JRASC/arXiv.](https://www.universetoday.com/wp-content/uploads/2013/04/history.jpg)