Hubble Views the Star that Changed the UniverseOn the night of October 5 1923, the US astronomer Edwin Hubble identified the first Cepheid variable star in the Andromeda galaxy. This proved that the galaxy was not part of the Milky Way.
Though the universe is filled with billions upon billions of stars, NASA's Hubble Space Telescope has been trained on a single variable star that in 1923 altered the course of modern astronomy
The star goes by the inauspicious name of Hubble variable number one, or V1
, and resides two million light-years away in the outer regions of the neighboring Andromeda galaxy, or M31
. V1 is a special class of pulsating star called a Cepheid variable that can be used to make reliable measurements of large cosmic distances.
The star helped Edwin Hubble
show that Andromeda lies beyond our galaxy. Prior to the discovery of V1 many astronomers, including Harlow Shapley
, thought spiral nebulae, such as Andromeda, were part of our Milky Way galaxy. Others weren't so sure. In fact, Shapley and Heber Curtis
held a public debate in 1920 over the nature of these nebulae. But it took Edwin Hubble's discovery
just a few years later to settle the debate.
The following text is excerpted from the article "Hubble Views the Star that Changed the Universe"
For example, Andromeda
, the largest of the spiral nebulae, presented ambiguous clues to its distance. Astronomers had observed different types of exploding stars in the nebula. But they didn't fully understand the underlying stellar processes, so they had difficulty using those stars to calculate how far they were from Earth. Distance estimates to Andromeda, therefore, varied from nearby to far away. Which distance was correct?Edwin Hubble was determined to find out
The astronomer spent several months in 1923
scanning Andromeda with the 100-inch Hooker telescope, the most powerful telescope of that era
, at Mount Wilson Observatory in California. Even with the sharp-eyed telescope, Andromeda was a monstrous target, about 5 feet long at the telescope's focal plane. He therefore took many exposures covering dozens of photographic glass plates to capture the whole nebula.
He concentrated on three regions
. One of them was deep inside a spiral arm. On the night of Oct. 5, 1923,
Hubble began an observing run that lasted until the early hours of Oct. 6. Under poor viewing conditions, the astronomer made a 45-minute exposure that yielded three suspected novae, a class of exploding star. He wrote the letter "N," for nova,
next to each of the three objects.Later, however, Hubble made a startling discovery when he compared the Oct. 5-6 plate
with previous exposures of the novae. One of the so-called novae dimmed and brightened over a much shorter time period than seen in a typical nova.
Hubble obtained enough observations of V1
to plot its light curve, determining a period of 31.4 days, indicating the object was a Cepheid variable. The period yielded the star's intrinsic brightness, which Hubble then used to calculate its distance. The star turned out to be 1 million light-years from Earth, more than three times Shapley's calculated diameter of the Milky Way.
Taking out his marking pen, Hubble crossed out the "N" next to the newfound Cepheid variable and wrote "VAR,"
for variable, followed by an exclamation point.For several months the astronomer
continued gazing at Andromeda, finding another Cepheid variable and several more novae. Then Hubble sent a letter along with a light curve of V1 to Shapley telling him of his discovery. After reading the letter, Shapley
was convinced the evidence was genuine. He reportedly told a colleague, "Here is the letter that destroyed my universe."
By the end of 1924 Hubble had found 36 variable stars in Andromeda, 12 of which were Cepheids.
Using all the Cepheids, he obtained a distance of 900,000 light-years. Improved measurements now place Andromeda at 2 million light-years away.
► Read more>>http://www.nasa.gov/mission_pages/hubble/science/star-v1.html
► About the image
Views of a famous pulsating star taken nearly 90 years apart and a portrait of its galactic home are shown in this image collection.
The pancake-shaped disk of stars, gas, and dust that make up the Andromeda galaxy, or M31, is shown in the image at left. Andromeda is a Milky Way neighbor and resides 2 million light-years away.
The tiny white box just above center outlines the Hubble Space Telescope view. An arrow points to the Hubble image, taken by the Wide Field Camera 3. The snapshot is blanketed with stars, which look like grains of sand.
The white circle at lower left identifies Hubble variable number one, or V1, the Cepheid variable star discovered by astronomer Edwin Hubble in 1923. Cepheid variables are pulsating stars that brighten and fade in a predictable pattern. Astronomers use them to calculate how far away they are from Earth.
The large white box outlines the region imaged by astronomer Edwin Hubble, who used the 100-inch Hooker telescope, the most powerful telescope of that era. An arrow points to a copy of Hubble's image of Andromeda, which was made on a 4-inch-by-5-inch glass plate and dated Oct. 6, 1923
► Illustration Credit: NASA, ESA, and Z. Levay (STScI)Source>> http://hubblesite.org/newscenter/archive/releases/2011/15/image/d/
► News release images>> http://hubblesite.org/newscenter/archive/releases/2011/15/image/
► Further readinghttp://hubblesite.org/hubble_discoveries/science_year_in_review/pdf/2011/revisiting_star_v1.pdfhttp://www.space.com/11761-historic-star-variable-hubble-telescope-photo-aas218.htmlhttp://www.smithsonianmag.com/history/how-edwin-hubble-became-the-20th-centurys-greatest-astronomer-66148381/http://oregonstate.edu/instruct/hsts414/doel/Hubble_Transformation_Cosmology.pdfhttp://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/hubble-edwin.pdfhttp://www.as.utexas.edu/astronomy/education/fall06/bromm/secure/lecture22.pdf #history_of_science #Edwin_Hubble #universe #cepheid_stars #first_cepheid_variable_star #astronomy #space