Robert McNees
VAR!
In the early morning hours #OTD in 1923, Edwin Hubble took a photo plate of M31 showing a Cepheid variable star.
Using Henrietta Swan Leavitt’s distance-luminosity relationship, Hubble concluded that M31 is located outside the Milky Way.
This observation established that there are other galaxies besides our Milky Way, that our little island is not the whole Universe.
Image: Carnegie Observatories
Robert McNees
You can see three marks "N" on the plate where Hubble identified novae.
Comparing with a plate taken the night before, he realized that the brightness of one was changing. Recognizing a Cepheid variable star, he crossed out the "N" and wrote ‘VAR!’
Here are the plates side-by-side. H331H was taken the previous night, a 40-minute exposure with poor seeing conditions. Plate H335H, which revealed the Cepheid, was a slightly longer exposure under better conditions.
Image: Carnegie Observatories
:mastodonworld: Petabites
@mcnees you mean a hundred years ago, people thought the Milky Way was everything?
(and by "people" I mean the best astronomers)
Robert McNees
@HoustonDog There was debate. But definitive proof was collected 100 years ago today. He would announce it a bit later.
Robert McNees
Here is a blink comparator gif of the two plates, switching back and forth with a 1s interval and cropped to show the region with the Cepheid variable.
Do you think you would have spotted it?
The images I have access to have been compressed, and the quality isn't too high, so it becomes almost impossible to see it on the screen. It would have been more apparent (though still very faint) on the original plate.
Robert McNees
@zleap Yes, that's exactly what these were.
Paul Sutton
I like the fact we still use the term 'plates' to refer to images in science, even in some papers. Is this term derived from the fact that early cameras used plates, covered in ligh sensitive chemicals to take the photos. ?
Robert McNees
(Hopefully this gif is displaying correctly for you. It alternates frames at 1s intervals in the preview, but in the actual post my client is showing a much different delay.)
Robert McNees
About ten years ago, the Hubble Space Telescope was pointed at M31 to record an image of the star. Here's an Earth-based photo of the galaxy with insets showing the region imaged by HST, and the region covered by the Var! plate.
The copy of Hubble's “Var!” plate in this image has been enhanced to make the star much more visible.
Image: R. Gendler, NASA, ESA, Hubble Heritage Team (STScI/AURA)
Chirp! is a social network. It runs on GNU social, version 2.0.1-beta0, available under the GNU Affero General Public License.
All Chirp! content and data are available under the Creative Commons Attribution 3.0 license.