#Henrietta Swan Leavitt

[teachersource]

Henrietta Swan Leavitt was born on July 4, 1868. An American astronomer and graduate of Radcliffe College, she worked at the Harvard College Observatory as a "computer", tasked with examining photographic plates in order to measure and catalog the brightness of stars. This work led her to discover the relationship between the luminosity and the period of Cepheid variables. Leavitt's discovery provided astronomers with the first "standard candle" with which to measure the distance to faraway galaxies, up to about 20 million light years.

[garadinervi]

Erika Blumenfeld, Tracing Luminaries: Plate No. AM1079 (Variable star in Pegasus & Markab), (one of a portfolio of six intaglio prints created from laser engraved cast acrylic plates inked with transparent base, printed onto a direct starlight-exposed cyanotype chine collé using Okuwara paper, bonded to Hahnemühle Copperplate backing paper, with printed ink gilded with 24-karat gold leaf), 2022 [© Erika Blumenfeld]

/ Plate Description /

Observatory: Harvard Boyden Station, Arequipa, Peru Telescope: 1-inch, 1.5-inch Cooke Lenses Date Exposed: 02 October 1901 Class: L Right Ascension: 23 hours, 00 (1855) minutes Declination: +15.1 degrees Quality: 3 Exposure: 61 minutes

Plate Events: Marks removed; plate scanned for DASCH (2019-04-25T17-40-34).

Marked by: This plate appears to have been marked by one, possibly two women, although no initials appear on the plate jacket and thus their identities are not known for certain. However, the plate was used in Henrietta Swan Leavitt's research, and it is possible that she and/or her assistants made the markings.

Curatorial & Astronomical Notes: This plate appears on page 28, dated 06 October 1904 in Henrietta Swan Leavitt's notebook titled "Miscellaneous Observations" which spans the years 1904 to 1910. The star that is encircled by the woman's mark is Markab, which is the third-brightest star in the constellation Pegasus. The star that the tail of the woman's mark is pointing to is a variable star, today known as HD 218155.

[lightningderg]

Henrietta Swan Leavitt! I had to paint her for a school research project! I have to say, this is probably one of my favorite IRL paintings ever haha

[foone]

I want a human zoology textbook.

Zoology, as in the study of animals. Like, a study of how humans work, done by an author that is not human.

I specifically want this for a couple reasons:

1. Descriptive, not prescriptive: don't tell me what the author thinks humans should do or how they should be. Tell me what they do. Observationally!

2. No bias towards "nature". I don't particularly care what the author is imagining humans are like in some "garden of eden" unfallen state. I want it to reference how humans ARE.

3. No morality applied to this! What do humans DO, not what you think they should do, or how they should be. And most importantly, no self-censorship in order to avoid offending some of the humans that disagree with ways people live.

And the reason I want this is because of how biology textbooks/wiki pages get written, where even if they try to be progressive they're still written from this weird perspective where they're explaining based on old ideas and the progressive stuff gets a footnote.

Like it'll be "humans have two genders, male and female. This is determined from their chromosomes, XY for male and xx for female."

And then you scroll past two pages for men and another two pages for women, and then it has one subsection that covers non-binary people and intersex people. And it's like: well then integrate that into your main statement!

It's like the author's worldview is still "there's two genders and everyone is born as one" but they've been forced to accept there are some weird exceptions but the core worldview is unchanged. And it's understandable! Wrong, but understandable: the grew up in a world that is quite strong on the "there are only two genders" ideology and doesn't like to remember that intersex people exist.

But like, imagine if you tried to do this as a zoologist. You're like "hey, all bees are female!" and then someone points out the rare male drones and they're like "oh okay I'll update my zoology textbook."

And now it reads:

All bees are female. Most are workers, and one is the queen.

(a couple sections go pass)

Drones: recent science has discovered that some bees are born male. These rare exceptions live short lives where they fertilize a queen and then die.

And it's like, no? Drones are very important to how a hive lives and they can't survive without them?

And we're constantly doing the same thing to humans and it's just bad science. Like, sure, maybe you could have the theory that "humans come in two genders: male and female" but as soon as you see one non-binary person, you have to discard that theory: it has been proven false! It's like not believing in other galaxies after Henrietta Swan Leavitt figured out how Cepheid Variables worked.

Add to that the "nature" thing. Like, you can make a sort of argument about nature vs artificial settings for a lot of species: the whole alpha/beta wolf thing came about because it turns out wolves act differently in captivity compared to the wild, so it makes sense to study how the vast majority of wolves live, not a small group you stuffed into a small area with unusual conditions. It's like saying the lifespan of goldfish is under 5 minutes, based on your study of them in this dry box you put them in.

But humans are different: we are tool-users who build new environments for ourselves. And while you can talk about how humans living in different environments act differently, it doesn't make a lot of sense to call one of them "artificial". All of them are made by us, and humans always do this. This means all environments are natural (because building environments for ourselves is what we naturally do) and all environments are artificial: we always alter our environments to better suit us! That's one of the things we naturally do!

And as for morality, it's about not ignoring things humans do regularly because you think it's weird or you think they shouldn't.

Like that tweet where someone pointed out that lots of species can change gender. Clown fish are a big one, some frogs, a couple birds, some lizards, and humans.

And people often have an immediate knee-jerk reaction of "that doesn't count!" for the last entity in that list. Why? Because we do it (usually) with clothes and makeup and medication, instead of just "naturally"? Bullshit. We're naturally TOOL USERS. Of course we use tools to change gender. We use tools to do EVERYTHING. That's natural for us.

So yeah. I think it'd be refreshing and enlightening to have a zoology textbook written about humans with this detached non-human perspective. An unbiased description of what humans are and do, rather than one irrevocably tinged with ideas of what humans should be and should do.

Basically I want to load up Vulcan Wikipedia and check the "Humans" article.

[everythingismadeofchaos]

This is my list of (IMHO) genuinely heroic people. I keep this list so that when I'm feeling uninspired I can pick a name at random, look them up, and be inspired. My memory kinda sucks so I've usually forgotten about them in the interim so it's like hearing some inspiring story for the first time. Please feel free to use this list for that purpose or for whatever purpose helps you. This is a private thing I've been absent-mindedly curating for years, so it's a little discombobulated; maybe I should put it in alphabetical order, for example. Since it works for what I use it for, though, I've never had the need for that, although there may be some duplicates specifically because of that.

If you have any additions, I'd love to hear them.

If you know of a reason somebody should not be on here, I'd love to hear that too. There are some controversial choices here, some people I've hemmed and hawed about, but in the end they're still on the list.

In no particular order:

Rachel Corrie

Aaron Bushnell

Sophie Scholl

Irena Sendler

Eugeniusz Łazowski

Mary Schweitzer. I know who she is but I'm including her anyway. Takes guts to do what she did

Temar Boggs

Juan Pujol García

Warrant Officer Hugh Thompson

Temar Boggs

Henrietta Swan Leavitt

Aitzaz Hassan Bangash Shaheed. Might already be on here; I need to alphabetize this list

Sal Khan. Yeah, I'm including him

Irena Sendler

Neerja Bhanot

Iqbal Masih

Tank man

Stephen Ruth. The guy with the cameras. He's no tank man, but why not, he's on the list

Narendra Dabholkar

Dietrich Bonhoeffer

Sophie Scholl

Charles Hazlitt Upham

Wang Weilin

John Rabe (? ... Kind of questionable for obvious reasons. He saved a couple hundred thousand Chinese people though. I don't know. He was what he was.)

Baron Jean Michel P.M.G. de Selys Longchamps, DFC

Aitzaz Hasan Bangash

Daniel Hale

Hannie Schaft

Reality Winner … I guess

Aki Ra

Norman Borlaug

Neil Armstrong

Stanislav Petrov

Vasili Alexandrovich Arkhipov

William Kamkwamba

Donald A Henderson

Freddie Oversteegen

Daryl Davis and his collection of robes

Jacinto Convit

Sir Nicholas Winton

August Landmesser

Jonas Salk

Carl Lutz

Giorgio Perlasca

Derrick Nelson, principal of Westfield High School in New Jersey

Giles Corey

Chiune Sugihara

Sophie Scholl

Ronald McNair? Why not

Corollary:

I'm not sure how to phrase "the opposite of this list," so I'm just going to call it the opposite of this list. Genuinely villainous people? Too easy, and honestly not what I'm going for. Anyway, I'm going to leave out the obvious like Hitler, Trump and Gaddafi because they're, well, obvious. Actually I'm not really sure what the goal of this list is so I'm just kind of winging it. People not to emulate?

Marvin Heemeyer

[warriorteam1924]

Somebody’s watching me

featuring Joe Mazzello & Swan

Author note : Hello my beauties. I'm back for another tiny piece for halloween ^^ ! I’ve been super busy lately and I’m aware it’s not my best piece, but  I hope some of you will enjoy it anyways. Using someone else's gif should give you an idea of how I'm running everywhere. Thanks in advance to anyone who will be giving honest feedback, it’s always very appreciated. Also, I remind you English isn’t my mother tongue, apologies in advance for the mistakes.

Warnings : none really, just my awful writing

Summary : a thrill with Joe Mazzello

Words count : 1,729 words

Permanent taglist : @reavenedges-lies @thosequeenboys @orionis8689 (apologies people, i removed you from the list, since you don't interact.... i asked for communication....)

It was yet another random day for Joe when he woke up that day. Morning coffee and breakfast, shower, hairstyling. Nothing very unusual. He wasn’t currently busy with work so he spent his days between his computer, his console or watching random series or movies. Maybe at some point it would give him an idea for a future working project. Of course, he wasn’t to feel sorry for. Money wasn’t an issue. He had his friends he could see now and then. His family was close to him and he could pay a visit every now and then. Life was good. Or at least, that’s what he was thinking so far.

He took his phone to take a picture, a silly one obviously, to send his friend. After taking a few ones, he opened the gallery application and smiled at his own silliness, when he saw his selfies with his tongue sticking out.

He was still genuinely smiling when panic erased his grin. There was a picture on his phone, a picture he was sure he didn’t take. He was absolutely certain he hadn’t taken it since it was a picture of him sleeping. The issue was, he was living alone. And there was not a chance of someone like a robber or a random intruder would be able to enter his house. Joe was living on his own and made sure to lock doors and windows at night. There was no reason to tempt fate. Those things didn’t happen only to others. Besides, he had also installed a few security cameras.

In this picture, he was peacefully sleeping, curled up in his blanket. There was no doubt, it was him and his bedroom. What on earth had happened?

Joe was firmly frowning. He decided to delete all the silly selfies he had taken, leaving the suspicious picture on top of his gallery. He had no important plans for the day, so it was the right time to investigate.

He sat in front of his computer and plugged his phone. He logged on several sites such as his mailbox, his social accounts and other online shopping sites. Apparently, all was still normal, meaning no one had hacked his accounts.

He hadn’t been very keen on doing so but some time ago, he also had installed an artificial intelligence to connect his different devices, and it also helped him manage his security cameras. He had chosen a feminine name, Swan, but it was also a dedication to Henrietta Swan Leavitt, famous American astronomer. It wasn’t super fancy, but it was yet another occasion to bring up an interesting topic when someone was coming over and he was using his A.I.

“Swan?”, he asked like he usually did.

“Yes, Joe?”, the feminine voice replied, like it usually did.

“Did you spot anything special last night while I was sleeping? Was there anything strange or unusual?”, he questioned.

“One moment, please”, Swan replied.

Joe knew that Swan needed time to search the files and check them all. The robotic voice spoke again.

“Nothing unusual was found. Are you looking for something specific?”.

“I was just wondering if someone had entered the house?”, Joe asked.

“No intruder or uninvited person was recorded on the files.”, the voice affirmed again.

Joe frowned again. His phone rang and a reminder let him know he had planned to see a friend, unlike what he had thought in the morning. Trying not to think about it, he got ready and went to meet his friend.

It was actually his best friend, so Joe thought about showing him the mysterious pic and asking him for advice. They had known each other for a very long time, it was worth trying.

Mentioning it in the conversation, Joe took his phone out of his pocket and unlocked it and opened the gallery app to show it to his friend. The latter looked at it and he frowned.

“Are you kidding me, mate?”, he asked.

“What ?”, Joe replied.

“There isn’t such a pic in your gallery dude….”, the other said as he handed him his phone.

“What the….”, Joe didn’t finish his sentence.

He scrolled and searched his gallery, several times, he even looked in the trash folder, thinking maybe he had accidentally deleted it. But he found nothing.

The rest of the time dedicated to his friend was nothing but Joe daydreaming and nodding, as he wasn’t really paying attention to what his friend was saying.

At some point, Joe pretended to be tired and went back home. He was worried and concerned. Had he lost his mind?

Still trying not to think about the mysterious picture, Joe watched his feel-good movie and went to bed, after checking his bedroom all the same, just to make sure there wasn’t a camera or anything he hadn’t seen before. Yet, there was nothing he hadn't installed, no device in the room to take a picture of him.

The following morning, he woke up as he usually did, thinking about his daily tasks. There was no notification on his phone, but he wanted to make sure the previous day only happened in his mind, that it tricked him when seeing the mysterious picture.

What was his horror when he saw another picture of him, again, sleeping tightly in his bed. Panic invaded him again, shaking his body and making him sweat. His breath was heavy and he had to fight the severe anxiety that was threatening him.

He got up, and again, went on his laptop to check again his various accounts. Again, nothing unusual was to be noted. He asked Swan to give him access to the security cameras. It was possible the day before that, the artificial intelligence had missed something.

Swan gave him access to the videos and he fast-forward looked at them. All the cameras showed nothing but a calm night in the surroundings. A street cat was seen on one camera, but Joe made sure to look at all the videos and he saw nothing. No intruder, no one who had been able to unlock his phone, take a picture of him, put his phone back and leave. Besides, his phone was to be unlocked with his fingerprint, there was no way he wouldn’t have felt it.

Again, he asked Swan a few questions, making sure he, too, hadn’t missed anything. It replied with his feminine and robotic voice.

“There was nothing unusual last night, Joe. Can I help you in any way?”.

“I’m starting to wonder if I’m going crazy….”, Joe mumbled, more to himself rather than a proper reply to the A.I. that was now in his life.

“You’re not crazy, Joe. You’re a very nice man, funny, compassionate, smart. According to the social criteria, you are also very good looking. Anyone would feel good by your side.”, Swan replied all the same.

Joe had a fixed grin, but his worries were still there.

He thought about talking about it with other friends, or his family. But it would probably worry them. He also considered going to the police. But what if the picture disappeared again? They would surely think he was mental, even trying to draw attention on him. Or maybe that it would have been some kind of a joke.

Trying not to give way to panic, Joe wanted to try another night and try to stay awake longer. Maybe this way he would be able to witness someone with his own eyes.

Yet, despite having coffee and trying hard to stay up, Joe fell asleep. And of course, the following morning, there was a new pic of him sleeping on his phone.

Looking around him in his living room, Joe was very anxious and felt more and more confused. He couldn’t understand what was going on.

Speaking out loud to let his thoughts out, he said :

“I know !! I’m going to send the pictures to someone I trust and this way, the pic won’t only be on my device and they will believe me.”

Joe took his phone and selected the pic to send it to his friend. He called him in the meantime, making sure the latter had received the file. Yet, and to Joe’s greatest disappointment, his friend was getting nothing.

Joe thought maybe the file was corrupted or something, so he screencaped it and tried again to send it to his friend, miserably failing again and again.

“Let me know when you’re willing to be serious, mate.”, his friend said before hanging up, annoyed that Joe had disturbed him for nothing.

The following days weren’t very different from the previous ones. Joe went to bed and woke up with a new picture of him sleeping. One morning, the picture even included little heart emojis around him.

Joe had decided to go to the police, but as he had expected, when he arrived and tried to show his gallery, all the pictures taken of him while he was sleeping were gone.

He came back home, feeling isolated and losing it. That was it, it was official, he was becoming crazy.

“I’m going slightly mad, that’s for sure….”, he randomly said out loud. “What have I done to deserve that?”, he rhetorically asked, since he was on his own.

“You’ve done nothing wrong Joe. You’re a very nice man, funny, compassionate, smart. According to the social criteria, you are also very good looking. Anyone would feel good by your side.”, Swan said, and its sentences sounded very familiar.

“Yeah, yeah sure….”, Joe said. “Why bother, you’re nothing but a bot anyways….”, he concluded, before collapsing on the sofa.

Feeling like giving up, Joe started to cry. What was he supposed to do now? He heard his favorite song coming out of the speakers. Looking around, he feared the intruder was inside, but realized it was nothing but Swan that had heard him cry and tried to make him feel better.

“Thank you, Swan.”, Joe said, wiping the tears from his cheeks, slowly falling asleep again.

Joe was already snoring before the artificial intelligence could reply.

“I knew you’d like the music, Joe. I know you very well. But I’m surprised you didn’t like the pictures I took of you, to show you how much I love you. Soon, I’m going to show you I’m more than just a robot….”

[whataboutyouisamascot]

Hi z!!! 6 14 and 21 for ask game 🥰

Hello Drift! 🌿

6. The last dream you had

I honestly don’t know the last time I dreamed, haha. I’m not usually asleep long enough to make it to the REM stage, which makes dreams quite rare for me

14. The last food you ate

A handful of cashews before heading out the door for work

21. A random fact

The depth of the universe is a very recent discovery—the period-luminosity relation, which describes how the length of a star’s lumination corresponds to its distance from the Earth, was developed in 1908 by Henrietta Swan Leavitt, one of the first women to operate computers at Harvard. She would have gotten a Nobel prize for her discoveries, if she hadn’t passed away a few years before the nomination. (Never said it had to be a fact about me! 🌿)

Thank you for the asks!! 🫶

[sincerecinnamon]

THAT'S SO ADORABLE!! Absolutely in-love with that

Did you know the densest material in the universe is this hypothetical substance called nuclear pasta? It's ten billion times stronger than steel!

Ooh, I didn't!! That's interesting!

Did you know that Henrietta Swan Leavitt made discoveries about cephids that led to both discoveries of juet how vast the universe is AND led to the Hubble telescope?

(I know this because my school theatre group is doing a play about her, and I hope to get cast in it because I love the play so much! ^^)

[faerune]

i decided that steve and diana have five daughters all named after notable female scientists of history because i said so 🥰

henrietta - named after henrietta swan leavitt, an american astronomer who made discoveries about the luminosity of stars

marie - named after marie manynard daly, the first african american woman to earn a PhD in chemistry and who contributed a ton of knowledge of heart health

ada - named after ada lovelace

mina - named after mina bissell, an iranian-american scientist who researched breast cancer

alice - named after alice augusta ball who discovered a cure for leprosy (at only twenty-three)

[excepcionales]

Dato curioso: en la cara oculta de la luna hay un cráter de 65 km de diámetro denominado cráter Leavitt. Lleva el nombre de Henrietta Swan Leavitt, una astrónoma sorda de la Universidad de Harvard, y está dedicado a todas las personas sordas que han hecho contribuciones importantes a la ciencia

[teachersource]

Henrietta Swan Leavitt was born on July 4, 1868. An American astronomer and graduate of Radcliffe College, she worked at the Harvard College Observatory as a “computer”, tasked with examining photographic plates in order to measure and catalog the brightness of stars. This work led her to discover the relationship between the luminosity and the period of Cepheid variables. Leavitt’s discovery provided astronomers with the first “standard candle” with which to measure the distance to faraway galaxies, up to about 20 million light years.

[garadinervi]

Erika Blumenfeld, Tracing Luminaries: Tracing Luminaries: Plate No. B20645 (Small Magellanic Cloud), (one of a portfolio of six intaglio prints created from laser engraved cast acrylic plates inked with transparent base, printed onto a direct starlight-exposed cyanotype chine collé using Okuwara paper, bonded to Hahnemühle Copperplate backing paper, with printed ink gilded with 24-karat gold leaf), 2022 [© Erika Blumenfeld]

/ Plate Description /

Observatory: Harvard Boyden Station, Arequipa, Peru Telescope: 8-inch Bache Doublet, Voigtlander, reworked by Clark Date Exposed: 19 October 1897 Class: L Right Ascension: 0 hours 5 minutes (?) Declination: -74.1 degrees (?) Quality: 4 Exposure: 133 minutes (?)

Plate Events: Marks removed, likely around 2009-02-03T14:34:05; Plate not scanned for DASCH; Plate was added to The Williamina Fleming Collection, a collection created to preserve around 600 marked plates, even though the marks from this plate had been removed.

Marked by: This plate was marked by Henrietta Swan Leavitt and possibly her assistants.

Curatorial & Astronomical Notes: This plate was used in Henrietta Swan Leavitt’s 1908 groundbreaking paper titled, 1777 Variables in the Magellanic Clouds, which compared Cepheid variable stars, and eventually led to her far-reaching discovery of the period-luminosity relationship. This plate number is noted on pages 9 (13 April), 19 (14 April), 31 (15 April), 37 (17 April), 49 (18 April), 54 (18 April), 67 (19 April), 87 (25 April), 94 (27 April), 108 (28 April), 110 (29 April), 112 (29 April), 117 (10 may), 131 (16 June), 150 (04 October) in Leavitt’s 1905 notebook.

[mirandamckenni1]

... a zaszczyty zebrali mężczyźni - Zjawisko Matyldy 👉 Patronite ► https://ift.tt/x04apwR 📚 Moja książka ► https://ift.tt/EZ9puBk 📚 E-book ► https://ift.tt/K1PuUca 🎧 Mix audio ► http://ratstudios.pl/ Wielu analityków zwraca uwagę na pewne niepokojące zjawisko, nazywane zjawiskiem Matyldy. Pod tym pojęciem rozumie się przypadki, w których, pomimo wymiernego udziału kobiet w badaniach naukowych, uznanie i nagrody przypadają mężczyznom. Historia pokazuje, że takie przypadki z całą pewnością miały i mają miejsce. Ich skala momentami poraża... 🎞 Dyfrakcja w badaniu kryształów https://www.youtube.com/watch?v=rbEo2tSS3XU 🎞 Odkrycia amatorów https://www.youtube.com/watch?v=Ppom9P24Yb8 Subskrypcja ► https://youtube.com/c/UwagaNaukowyBelkot Facebook ► https://ift.tt/8enzXlZ Twitter ► https://twitter.com/NaukowyBelkot Instagram ► https://ift.tt/UFbqvan Wyłącznie Naukowy Bełkot ► https://goo.gl/Do7VCc Grupa na facebooku ► https://goo.gl/HP8J83 === Rozkład jazdy: 0:00 Wstęp 2:05 Miejsce 5 6:10 Miejsce 4 9:03 Miejsce 3 12:16 Miejsce 1 16:25 Miejsce 1 19:20 Podsumowanie === Źródła: Forgotten Women. The Scientists, Zing Tsjeng, Cassell Illusrtated, 2018 Życie w cieniu. Historia Lise Meitner, Tomasz Pospieszny https://ift.tt/yE95FA7 Rosalind Elsie Franklin. Biography. U.S. National Library of Medicine. https://ift.tt/MATP3k7 Rosalind Franklin: A Crucial Contribution, Scitable by Nature Education, https://ift.tt/IQ0PsS1 The Women Who Mapped the Universe And Still Couldn’t Get Any Respect, Natasha Geiling, SMITHSONIANMAG.COM, 2013 Henrietta Swan Leavitt, From Wikipedia, the free encyclopedia, https://ift.tt/erDnGJs Encyclopaedia Britannica https://ift.tt/SB6lbc0 13 niezwykłych kobiet nauki, które zmieniły świat, https://ift.tt/muGsyxT Encyclopaedia Britannica, https://ift.tt/n0iy3Sr Chien-Shiung Wu, Madame Wu, Tomasz Pospieszny, 2021, https://ift.tt/HoUn9k4 Tydzień Noblowski — wielkie niedocenione, Tomasz Pospieszny, 2020, https://ift.tt/uSjC83I via YouTube https://www.youtube.com/watch?v=4NCA2ABYv90

[spacetimewithstuartgary]

What is dark energy? Inside our accelerating, expanding universe

Some 13.8 billion years ago, the universe began with a rapid expansion we call the Big Bang. After this initial expansion, which lasted a fraction of a second, gravity started to slow the universe down. But the cosmos wouldn't stay this way. Nine billion years after the universe began, its expansion started to speed up, driven by an unknown force that scientists have named dark energy.

But what exactly is dark energy?

The short answer is: We don't know. But we do know that it exists, it's making the universe expand at an accelerating rate, and approximately 68.3% to 70% of the universe is dark energy.

It all started with Cepheids

Dark energy wasn't discovered until the late 1990s. But its origin in scientific study stretches all the way back to 1912 when American astronomer Henrietta Swan Leavitt made an important discovery using Cepheid variables, a class of stars whose brightness fluctuates with a regularity that depends on the star's brightness.

All Cepheid stars with a certain period (a Cepheid's period is the time it takes to go from bright, to dim, and bright again) have the same absolute magnitude, or luminosity—the amount of light they put out. Leavitt measured these stars and proved that there is a relationship between their regular period of brightness and luminosity. Leavitt's findings made it possible for astronomers to use a star's period and luminosity to measure the distances between us and Cepheid stars in far-off galaxies (and our own Milky Way).

Around this same time in history, astronomer Vesto Slipher observed spiral galaxies using his telescope's spectrograph, a device that splits light into the colors that make it up, much like the way a prism splits light into a rainbow. He used the spectrograph, a relatively recent invention at the time, to see the different wavelengths of light coming from the galaxies in different spectral lines. With his observations, Silpher was the first astronomer to observe how quickly the galaxy was moving away from us, called redshift, in distant galaxies. These observations would prove to be critical for many future scientific breakthroughs, including the discovery of dark energy.

Redshift is a term used when astronomical objects are moving away from us and the light coming from those objects stretches out. Light behaves like a wave, and red light has the longest wavelength. So, the light coming from objects moving away from us has a longer wavelength, stretching to the "red end" of the electromagnetic.

Discovering an expanding universe

The discovery of galactic redshift, the period-luminosity relation of Cepheid variables, and a newfound ability to gauge a star or galaxy's distance eventually played a role in astronomers observing that galaxies were getting farther away from us over time, which showed how the universe was expanding. In the years that followed, different scientists around the world started to put the pieces of an expanding universe together.

In 1922, Russian scientist and mathematician Alexander Friedmann published a paper detailing multiple possibilities for the history of the universe. The paper, which was based on Albert Einstein's theory of general relativity published in 1917, included the possibility that the universe is expanding.

In 1927, Belgian astronomer Georges Lemaître, who is said to have been unaware of Friedmann's work, published a paper also factoring in Einstein's theory of general relativity. And, while Einstein stated in his theory that the universe was static, Lemaître showed how the equations in Einstein's theory actually support the idea that the universe is not static but, in fact, is actually expanding.

Astronomer Edwin Hubble confirmed that the universe was expanding in 1929 using observations made by his associate, astronomer Milton Humason. Humason measured the redshift of spiral galaxies. Hubble and Humason then studied Cepheid stars in those galaxies, using the stars to determine the distance of their galaxies (or nebulae, as they called them).

They compared the distances of these galaxies to their redshift and tracked how the farther away an object is, the bigger its redshift and the faster it is moving away from us. The pair found that objects like galaxies are moving away from Earth faster the farther away they are, at upwards of hundreds of thousands of miles per second—an observation now known as Hubble's Law, or the Hubble-Lemaître law. The universe, they confirmed, is really expanding.

Expansion is speeding up, supernovae show

Scientists previously thought that the universe's expansion would likely be slowed down by gravity over time, an expectation backed by Einstein's theory of general relativity. But in 1998, everything changed when two different teams of astronomers observing far-off supernovae noticed that (at a certain redshift) the stellar explosions were dimmer than expected. These groups were led by astronomers Adam Riess, Saul Perlmutter, and Brian Schmidt. This trio won the 2011 Nobel Prize in Physics for this work.

While dim supernovae might not seem like a major find, these astronomers were looking at Type 1a supernovae, which are known to have a certain level of luminosity. So they knew that there must be another factor making these objects appear dimmer. Scientists can determine distance (and speed) using an objects' brightness, and dimmer objects are typically farther away (though surrounding dust and other factors can cause an object to dim).

This led the scientists to conclude that these supernovae were just much farther away than they expected by looking at their redshifts.

Using the objects' brightness, the researchers determined the distance of these supernovae. And using the spectrum, they were able to figure out the objects' redshift and, therefore, how fast they were moving away from us. They found that the supernovae were not as close as expected, meaning they had traveled farther away from us faster than anticipated. These observations led scientists to ultimately conclude that the universe itself must be expanding faster over time.

While other possible explanations for these observations have been explored, astronomers studying even more distant supernovae or other cosmic phenomena in more recent years continued to gather evidence and build support for the idea that the universe is expanding faster over time, a phenomenon now called cosmic acceleration.

But, as scientists built up a case for cosmic acceleration, they also asked: Why? What could be driving the universe to stretch out faster over time?

Enter dark energy.

What exactly is dark energy?

Right now, dark energy is just the name that astronomers gave to the mysterious "something" that is causing the universe to expand at an accelerated rate.

Dark energy has been described by some as having the effect of a negative pressure that is pushing space outward. However, we don't know if dark energy has the effect of any type of force at all. There are many ideas floating around about what dark energy could possibly be. Here are four leading explanations for dark energy. Keep in mind that it's possible it's something else entirely.

Vacuum energy

Some scientists think that dark energy is a fundamental, ever-present background energy in space known as vacuum energy, which could be equal to the cosmological constant, a mathematical term in the equations of Einstein's theory of general relativity. Originally, the constant existed to counterbalance gravity, resulting in a static universe. But when Hubble confirmed that the universe was actually expanding, Einstein removed the constant, calling it "my biggest blunder," according to physicist George Gamow.

But when it was later discovered that the universe's expansion was actually accelerating, some scientists suggested that there might actually be a non-zero value to the previously-discredited cosmological constant. They suggested that this additional force would be necessary to accelerate the expansion of the universe. This theorized that this mystery component could be attributed to something called "vacuum energy," which is a theoretical background energy permeating all of space.

Space is never exactly empty. According to quantum field theory, there are virtual particles, or pairs of particles and antiparticles. It's thought that these virtual particles cancel each other out almost as soon as they crop up in the universe, and that this act of popping in and out of existence could be made possible by "vacuum energy" that fills the cosmos and pushes space outward.

While this theory has been a popular topic of discussion, scientists investigating this option have calculated how much vacuum energy there should theoretically be in space. They showed that there should either be so much vacuum energy that, at the very beginning, the universe would have expanded outwards so quickly and with so much force that no stars or galaxies could have formed, or… there should be absolutely none. This means that the amount of vacuum energy in the cosmos must be much smaller than it is in these predictions. However, this discrepancy has yet to be solved and has even earned the moniker "the cosmological constant problem."

Quintessence

Some scientists think that dark energy could be a type of energy fluid or field that fills space, behaves in an opposite way to normal matter, and can vary in its amount and distribution throughout both time and space. This hypothesized version of dark energy has been nicknamed quintessence after the theoretical fifth element discussed by ancient Greek philosophers.

It's even been suggested by some scientists that quintessence could be some combination of dark energy and dark matter, though the two are currently considered completely separate from one another. While the two are both major mysteries to scientists, dark matter is thought to make up about 85% of all matter in the universe.

Space wrinkles

Some scientists think that dark energy could be a sort of defect in the fabric of the universe itself; defects like cosmic strings, which are hypothetical one-dimensional "wrinkles" thought to have formed in the early universe.

A flaw in general relativity

Some scientists think that dark energy isn't something physical that we can discover. Rather, they think there could be an issue with general relativity and Einstein's theory of gravity and how it works on the scale of the observable universe. Within this explanation, scientists think that it's possible to modify our understanding of gravity in a way that explains observations of the universe made without the need for dark energy. Einstein actually proposed such an idea in 1919 called unimodular gravity, a modified version of general relativity that scientists today think wouldn't require dark energy to make sense of the universe.

The future

Dark energy is one of the great mysteries of the universe. For decades, scientists have theorized about our expanding universe. Now, for the first time ever, we have tools powerful enough to put these theories to the test and really investigate the big question: "What is dark energy?"

NASA plays a critical role in the ESA (European Space Agency) mission Euclid (launched in 2023), which will make a 3D map of the universe to see how matter has been pulled apart by dark energy over time. This map will include observations of billions of galaxies found up to 10 billion light-years from Earth.

NASA's Nancy Grace Roman Space Telescope, set to launch by May 2027, is designed to investigate dark energy, among many other science topics, and will also create a 3D dark matter map. Roman's resolution will be as sharp as NASA's Hubble Space Telescope's, but with a field of view 100 times larger, allowing it to capture more expansive images of the universe. This will allow scientists to map how matter is structured and spread across the universe and explore how dark energy behaves and has changed over time. Roman will also conduct an additional survey to detect Type Ia supernovae

In addition to NASA's missions and efforts, the Vera C. Rubin Observatory, supported by a large collaboration that includes the U.S. National Science Foundation, which is currently under construction in Chile, is also poised to support our growing understanding of dark energy. The ground-based observatory is expected to be operational in 2025.

The combined efforts of Euclid, Roman, and Rubin will usher in a new "golden age" of cosmology, in which scientists will collect more detailed information than ever about the great mysteries of dark energy.

Additionally, NASA's James Webb Space Telescope (launched in 2021), the world's most powerful and largest space telescope, aims to make contributions to several areas of research, and will contribute to studies of dark energy.

NASA's SPHEREx (the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) mission, scheduled to launch no later than April 2025, aims to investigate the origins of the universe. Scientists expect that the data collected with SPHEREx, which will survey the entire sky in near-infrared light, including over 450 million galaxies, could help to further our understanding of dark energy.

NASA also supports a citizen science project called Dark Energy Explorers, which enables anyone in the world, even those who have no scientific training, to help in the search for dark energy answers.

Lastly, to clarify, dark energy is not the same as dark matter. Their main similarity is that we don't yet know what they are.

TOP IMAGE....The history of the universe is outlined in this infographic. Credit: NASA

LOWER IMAGE....This composite image features one of the most complicated and dramatic collisions between galaxy clusters ever seen. Known officially as Abell 2744, this system has been dubbed Pandora's Cluster because of the wide variety of different structures found. Data from Chandra (red) show gas with temperatures of millions of degrees. In blue is a map showing the total mass concentration (mostly dark matter) based on data from the Hubble Space Telescope, the Very Large Telescope (VLT), and the Subaru telescope. Optical data from HST and VLT also show the constituent galaxies of the clusters. Astronomers think at least four galaxy clusters coming from a variety of directions are involved with this collision. Credit: NASA

[valkyries-things]

HENRIETTA SWAN LEAVITT // ASTRONOMER

“She was an American astronomer. A graduate of Radcliffe College, she worked at the Harvard College Observatory as a “computer”, tasked with examining photographic plates in order to measure and catalog the brightness of stars. This work led her to discover the relation between the luminosity and the period of Cepheid variables. This provided astronomers with the first “standard candle” with which to measure the distance to faraway galaxies.”