#86 is at collectSPACE – and features your favorite Alice’s Astro Info as hit number 2!

#85 is at Cheap Astronomy – and I’m not in it, but other awesome people are!

Hey … do you like Alice’s Astro Info?

Maybe you’d like to nominate me for Best New Weblog of 2008?

And yes, I have older archives than that, but I started this blog at ASP in June of 2008 – the archives are just old stuff I used to write and print out for staff at Pacific Science Center. I transferred them here for your perusal.

This guide is written to give hints to people who already know approximately what they’re looking at. For a good beginner’s guide to the sky, try StarDate, Sky and Telescope’s Stargazing Basics, or Sky and Telescope’s links to lots of beginning topics. (Or, if you know a better beginning stargazing site, put a link to it in a comment below!

This Month’s Starmap

Notable Sky Objects

VENUS

It may not be on my map, because the map is for later in the evening, but Venus is spectacular low in the southwest just after sunset. If you’ve got clear enough skies, poke your head out and learn why Venus has earned the moniker “the evening star.” (In a couple months you’ll be able to poke your head out early in the morning and learn why Venus ALSO earned the moniker “the morning star.”)

New Constellations

CANIS MAJOR – The Big Dog

SCIENCE: Obviously you’ll need to notice Sirius, the brightest star in the night-time sky, and if you’re wondering about that other one nearby, that’s Procyon. It’s not in Canis Major, it’s in Canis Minor (the little dog), but it’s nearby. If you have a new telescope (or an old one), Sirius might be a fun target, it’s bright enough to find with your scope semi-easily, and it’s a double star, so once you find it look for the teeeeensy-tinsey companion star. (I say “semi-easily” because learning to point a scope takes practice).

MYTH: Traditionally Canis Major and Minor are known as Orion’s hunting dogs, but children today will recognize something else in this constellation. The star Sirius is the inspiration behind the name of J.K. Rowling’s character Sirius Black in the Harry Potter series. Sirius Black is an animagus, a man who can turn himself into an animal. Guess what animal he becomes? Yup – a dog. A big, black dog. She knew her stuff.

According to Dr. Snowder at the Western Washington University Planetarium, the Chinook Tribe sees a canoe race in this part of the sky:

“A big canoe (Orion’s belt) and a small canoe (Orion’s dagger) are in a race to see who can be the first to catch a salmon in the Big River (Milky Way). The little canoe is winning the race. Can you tell which star is the fish? It is the very bright star in the middle of the river (Sirius).”

CANCER – The Crab

SCIENCE: Oh beautiful M44! Messier Object #44, the Beehive Cluster, is in the middle of Cancer. I have been told it’s called the Beehive because it’s full of little triangles of stars which look like bees swarming around.

MYTH: The ancient Egyptians saw Cancer as a scarab beetle – a symbol of life and immortality.

LEO – The Lion

SCIENCE: The star Wolf 359 is in Leo. It’s the third closest star to the Sun – and you might remember it from Star Trek fame – the Battle of Wolf 359, where the Federation attempts to hold off a Borg attack. The other closest stars are Alpha Centauri and Barnard’s Star. It’s too dim to see without a telescope or a camera, but it would be between Leo’s front and back feet.

Gliese 436 (I know, terrible names) is ALSO in Leo. There may be a small Earth-ish-like planet around this one – there’s definitely a Neptune-ish-like planet. We talked about a similar discovery a while ago – and this discovery is by the same team.

MYTH: The Khoisan people of South Africa call Regulus the “Fire Finisher.” It is a star that marks the time of night in the winter. Unfortunately, in the paper I read, the Fire Finisher might also be Antares or Arcturus – depending on which tribe you ask. Regulus is called “G/wi” – and I’m sorry, I can’t help you pronounce that, the “/” is an actual part of the anglicized spelling, because the Khoisan languages are the “clicky” languages of the San (Bushman) people. (This is from Astronomy Across Cultures, a book of scientific papers on traditional astronomy around the world. It’s an awesome book, and VERY hard to get a hold of).

“Tiny” Guys

Going for the Gold? Here’s this month’s itty-bittys.

LEPUS – The Hare

ERIDANUS  – The River (Actually, it’s huge, but dim)

CANIS MINOR – The Little Dog

LEO MINOR – The Small Lion (Between the Big Dipper and Leo)

CAMELOPARDALIS– The Giraffe

TRIANGULUM – The Triangle

ARIES – The Ram

SEXTANS – The Sextant

HYDRA – The Sea Serpent (Also big and dim, so big that it may be the biggest Northern Hemisphere constellation)

MONOCEROS – The Unicorn

LYNX – The Lynx

LACERTA – The Lizard

Returning Constellations

ORION – The Hunter

TAURUS – The Bull

GEMINI – The Twins

PISCES – The Fish

ANDROMEDA – Princess Andromeda

PEGASUS – The Winged Horse

CEPHEUS – King Cepheus

DRACO – The Dragon

URSA MAJOR – The Great Bear

URSA MINOR – The Little Bear

CASSIOPEIA – The Queen

Happy Sky Viewing!

Where’d I get my Info?

My memory, and Zeta Strickland

Selin, Helaine ed. Astronomy Across Cultures. Kluwer Academic Publishers. 2000.

Guest Writer: Jeremy Higgins, Planetarium and Stage Science Teacher Extraordinaire

Please enjoy this week’s AstroInfo, courtesy of Jeremy Higgins. He wrote our planetarium program on calendars (Ancient Skies, Ancient Eyes) that ran in conjunction with the Dead Sea Scrolls exhibit a couple years ago. Recently, probably inspired by the lack of Sun in Seattle, he’s been looking into calendars and tracking time a bit more, and found some interesting things. It’s a great article – and the short of it is: it’s pretty hard to make a well balanced calendar based on the Sun or the Moon, especially if you care about keeping dates and holidays in the same part of the year. Here it is, enjoy!

The Winter Solstice has arrived and passed. The days will begin to lengthen. The Sun won’t be setting at just after 4pm for very much longer. The Solstice is when the Sun stops rising and setting further to the South every day, instead beginning it’s 6 month long march to its northernmost rising and setting points. I am going through my yearly surprise at just how early this seasonal change causes The Sun to rise and set every day; we have sunset as early as 4:20pm in Seattle! The Solstices have been an important time of the year for cultures all around the world. It’s a good time to define just what we mean when we talk about the year.

What is a Year?

Generally, when we talk about a “year” we might assume that we are talking about the same thing. We might assume that we are discussing the 365.2425 days that it requires the Earth to recreate its path around the Sun. After all, this cycle gives us convenient points to mark out our seasonal changes. We can talk about the beginning of our seasons happening at certain points throughout the year. It’s very convenient. Except that for billions of people around the world, this calendar doesn’t mark their most important dates. The year one might assume we are referring to would be a year as marked out by the Gregorian calendar. This calendar was decreed by the Pope in 1582 for Catholic countries. The previous Julian calendar, itself an improvement on the Roman calendar, lost a day every 128 years. Additionally, in the beginning of its usage, the people responsible for implementing this calendar incorrectly added a leap day every 3 years. Whoops. That mistake having been resolved by skipping leap years for a while, there was an eleven day discrepancy. Someone would have to give up those days!

What’s the Problem?

As we can see, we begin to encounter calendar issues that could become very contentious. There is mythical rioting associated with the “stolen” eleven days in Europe. As we head back further, we start to see that the calendar reflects religious beliefs as well as civic needs. We can then move on to problems with holidays (holy days) arriving on the wrong days.

In the planetarium, when discussing the years, I ask people about different lengths of time. The conversation generally goes like this:

Me: What’s a year?
Visitors: 365 days… and, oh yeah, we add a day every four years.
Me: Right, it’s 365 and a quarter. Add those quarters up every four years and you get a dollar- or a day. Now, what’s a month?
Visitors: 30 days! 31 days! Er, 28 days! I mean sometimes 29 days!
Me: Wow, how can a month be all those different numbers of days? Aren’t units of time supposed to be the same? Isn’t a minute always 60 seconds? Isn’t an hour always 60 minutes…?
Visitors: Um, well… Don’t confuse me! Burn the witch! [that would be me they’re interested in burning]

Month – Moonth

I ask them to think about the word: month. If you stare at it for a long time, you might see an extra ‘o’ in the middle- moonth. Our moon has various cycles, but the one that is most visible from Earth is that of its phases. The moon takes roughly 29.5 days to go from one phase all the way back to that phase again. We can see that this cycle is close to the 30 (or so) day month. Now we see that we can create a calendar by sticking 12 of these nearly 30 day cycles together. However, to create a calendar like this, we’re going to have to give up those half days. You can’t have a half day on a calendar. It’s not like you’d get to go home early or something.

So, let’s make this Lunar calendar out of alternating months of 29 days and 30 days. If you’re scoring at home, you say, “Hey Guest AstroInfo guy, you are going to get really messed up, because if you string 12 of those moonths together, you’re going to end up with 354 days!” You’re right. Imagine you go 10 years with a calendar that is strictly a lunar calendar. You would end up more than 100 days off of the Tropical Year. (The Tropical Year is the year that is described when we talk about the Earth making one full revolution around the Sun, not the year you get to spend in Costa Rica). We could also call this a solar year. If this were to happen, we’d end up with winter holidays in the summer. Let’s burn the Yule Log, it’s only 75 degrees outside. (It would be the opposite in the Southern hemisphere).

In my opinion, the cycles of the moon are far easier and more convenient to follow. You can break your time increments up into smaller chunks. You can see that the moon made it into 28 locations in the sky throughout this time period. You can break the entire thing up into quarters. It’s pretty flexible. Still, you are left with the problem of the 11 day difference. Well, because many cultures have holidays with specific seasonal meaning, there would need to be a way to adjust for this problem.

Fixing the Lunar/Solar Mismatch

If we look specifically at the Hebrew calendar, we can see a solution. A “Leap Month,” or intercalary month, is added every 2 or 3 years to give 7 leap months every 19 years. It is a very convenient way of adjusting a lunar calendar to coincide with the mechanics of the Tropical Year. This creates a “lunisolar” calendar.

Here is where we see some area where disagreement may occur. If your calendar is one in which the days are being consistently switched around, you may end up with your holy days falling on the wrong kinds of days. According to the authors of the Dead Sea Scrolls, this was a problem. Part of the reason that the group who wrote the Dead Sea Scrolls separated themselves from the other Jewish people at the time was so that they could practice the use of their own calendar. The Dead Sea Scrolls describe a calendar which more closely aligns with a solar year. It allowed for holy days to fall on their correct kinds of days every year. Although, I must add that the year was described as being 364 days long, and there is no information as to what was done to correct for the missing day(s).

Who Uses a Lunar Calendar?

There are billions of people around the world who follow a lunar calendar. There is a Hindu lunar calendar, a Jewish lunar calendar, a Chinese lunar calendar… There are definitely other cultures which use a lunar calendar at least as historical perspective. The Islamic lunar calendar is a little different in that it specifically forbids the use of an intercalary month. Because of this, an important date on the Islamic calendar will be earlier by 11 days every year.

Calendars from Long Ago

We can meander back further to the creators of the first roughly 365 day calendar. The Egyptians used a calendar that was 365 days, but it was only indirectly based on the path of the Sun in the sky. This calendar relied upon the star we currently call Sirius. They watched this star for the time when it would first become visible in the sky before dawn. This rising of Sirius happened to roughly coincide with the flooding of the Nile. These ancient people watched the same thing happen every year- star rises, Nile floods, star rises, Nile floods. This is the kind of pattern that allowed the ancient Egyptians to create a calendar that roughly coincided with the 365 day calendar. One interesting note about this Egyptian calendar is that it had 36 “weeks” of 10 days each. Obviously, that ends up being short of their own 365 day period. What did they do with 5 extra days every year? What do you do when you have extra days? You have parties and festivals, right? So did the ancient Egyptians.

Clearly, this only scratches the surface of the change in calendrical thinking over the millennia. I invite you to research further points of interest in calendars.

Jeremy

Want More?

http://calendopedia.com/
http://en.wikipedia.org/wiki/Panchanga
http://www.ibiblio.org/expo/deadsea.scrolls.exhibit/Library/calend.html
http://www.webexhibits.org/calendars/calendar-islamic.html

An important holiday is coming up for many people of the world – Christmas. One of the many symbols of Christmas is the Star of Bethlehem; the star that was said to shine in the East guiding the shepherds, kings, and wise men to the bedside of the newborn Jesus Christ.

“What was that star?” is a question that has fascinated astronomers and non-astronomers for centuries. Setting aside all other questions, there are several possible astronomical events that happened between 20 B.C.E (Before Common Era) and 10 C.E. (Common Era) that could have been described as a “new star” by people of that time period.

Shooting Stars:

Shooting Stars aren’t stars at all, but falling bits of dust and sand burning up in our atmosphere – also known as meteors. They last a couple seconds at most, and are very common. You can see about seven meteors per hour on a normal night. Sometimes they can be very bright, but because they’re so common and short-lived, they probably don’t explain the Star of Bethlehem.

Comets:

European astronomers from around the year 1 didn’t pay much attention to comets, or keep detailed records of their appearances. Chinese astronomers were paying attention, calling them “broom stars,” and they recorded two such stars during the years in question: one in 5 B.C.E, and one in 4 B.C.E. Comets stay in the sky for weeks, are bright enough to be noticed even by everyday people, and look pretty weird if you’ve never seen one before. Plus they stay in almost the same location from day to day. Comets are a good possibility for the Star of Bethlehem, but they don’t look very star-like because they appear very fuzzy.

Comet of Bethlehem? Photo: NASA Edit:Alice

Planets:

Astronomers of the world knew about the planets and were able to track them long before 20 B.C.E. But, there is a possibility that the star of Bethlehem could have been a planet, especially when you start thinking about planetary conjunction which happens when two planets pass close to each other in our sky. When you combine two or three of the brightest planets in the sky (Jupiter, Mars, and Venus), that part of the sky that looks supernaturally bright – or at least catches your eye.
In 7 B.C.E. Jupiter and Saturn passed each other three times (a triple conjunction) within six months. This also happened in 1981 C.E. and will happen again in 2238 C.E. Not much later, in 6 B.C.E. Mars and Jupiter and Saturn all came very close to each other in our sky, a near conjunction. This was all very exciting if you knew what you were looking at (which the Magi did), but probably not that noticeable to everyday people.

Supernovae:

The last astronomical possibility is that the star was either a nova or a supernova. Either one would look like a surprisingly bright star that wasn’t there the night before, and would last for weeks or months. After a while the star would fade from view completely. Once again, European astronomers weren’t that great at recording supernovae, but the Chinese astronomers documented one that was visible in 14 B.C.E. This supernova would have been visible in the east just before sunrise (no star would stay in the east all night; as the earth turns everything in the night sky appears to move from east to west).

Added Section: We Don’t Know

Here’s another explanation for the Star of Bethlehem, courtesy of Steve White, one of our local awesome planetarians. I love it.

Steve says: “Okay, it’s not really an explanation at all, it’s just a category between ‘Comet/Planet/Supernova’ and ‘Miracle.’  There is, after all, a great big gap between ‘stuff we understand’ and ‘acts of God,’ and only a scientist too big for his/her britches would think otherwise.

“Astronomy is full of phenomena that, if not unexplained, used to be unexplained. In fact, we can only begin to explain certain astronomical phenomena that have occurred in the small number of centuries during which we’ve been looking. Any event rarer than that, a once-in-10,000-year event for example, or once-in-100,000-year event, or once-in-a-million year event, etc., would be utterly outside our explanatory capacity.

“Our theories and models may be precise enough to predict it, but not necessarily. If they are, our imaginations may fail us.

“The Star of Bethlehem may have been one of those. This doesn’t help us understand it, and is therefore unsatisfying… but, if we are going to [try to catalog all possibilities], we should consider the possibility of this sort of ‘Fortean’ phenomena as well.”

Miracle:

I feel the need to cover my bases here. I talked about the four different astronomical/astrological possibilities for the Star of Bethlehem, but I haven’t mentioned one very important possibility: a miracle, or something non-astronomical and inexplicable created by God or occurring simply because Jesus was being born. As a scientist, I can’t address this possibility (miracles don’t follow the laws of physics, there’s no test or math I can do to prove one way or the other), but since I don’t have a better explanation, you’re right, I can’t rule it out.

Historical Story:

Oof, ouch, this one is going to hurt a little bit, I’m sorry, but I do want to put it out there. Matthew (and Luke) are the ones who wrote most of the parts about the Star of Bethlehem (Read Matthew:2). My local doctor of medieval literature tells me that Matthew (and Luke) were written after Mark, and Mark was written after 66 C.E.
If Matthew was around during Jesus’s birth, then he’d be about 70, 80, or 90 years old when he wrote his account. Luckily for him, there was a comet (Halley) in 66 C.E., which would be fresh in his memory while he was writing about the Nativity.
Also, if Jesus was to be the Messiah it was prophesied that there would be a star at his birth. Matthew was writing for a Jewish audience, and part of what he was doing was probably trying to convince them that Jesus fulfilled these prophecies. It’s a lot easier for Jesus to fulfill the prophesy of being the Messiah if there’s a star at his birth. Did Matthew use the comet he had just seen as a prop to support his position that Jesus was the Messiah? Did Matthew tell the story as he’d heard it, through the lens of his recent experiences, including the comet as the star? I don’t know.

The Answer:

So what’s the answer? This is science, we don’t presume to know for sure. All of these are possibilities, and until there’s more evidence we have no way of picking one.

Want More?

http://science.nasa.gov/headlines/y2002/24may_duo.htm
http://science.nasa.gov/headlines/y2000/ast16may_1.htm
http://sciastro.net/portia/articles/thestar.htm (Reference from NASA)

Where’d I Get My Info?

Star of Bethlehem Planetarium Show for the Willard Smith Planetarium, December 1997, updated 2008
http://sciastro.net/portia/articles/thestar.htm

It’s time for the weekly carnival, hosted this week by Next Big Future!

We’re there, and thanks for your thoughtful comments on Aliens? Yes. UFOs? No.!!

Most of you don’t care, but for those of you who do, here’s a link to a map I’m making about the road quality during these icy conditions in West Seattle.

[googlemaps http://maps.google.com/maps/ms?ie=UTF8&hl=en&msa=0&msid=108064874253563525768.00045e6c7d8fab6caca49&ll=47.54943,-122.371023&spn=0.082187,0.07463&output=embed&s=AARTsJpF2poBEhBmylQEVgmlHKCO1BPqog&w=425&h=350]

It is based on comments posted in the threads on West Seattle Blog (the best place for super-current West Seattle News and Information)

On the topic of aliens and UFOs, I agree with the giants of astronomy education (Carl Sagan, Neil DeGrasse Tyson, and Phil Plait to name a few). Somewhere out there is life. It may or may not be intelligent, but it probably exists. Have “they” visited us? The possibility is vanishingly small. In short: Space is huge, it would be amazing if the right combination of our 120+ known elements only came together to form life here on Earth and nowhere else.

I’m going out on a limb. I’m not trained in rhetoric, so I expect my discussion to have major loopholes. I invite readers knowledgeable about this topic and knowledgeable about rhetoric to comment, and help me close up those loopholes. I would also like to point out that I started writing this article on November 18th, 2008 (I’ve been struggling with it for a long time). Phil wrote his post of the same title on November 25th, 2008. Whether you believe me or not, I’m not copying him.

Finding a Place to Live:

When we talk about alien life, we talk about “life as we know it.” Life as we know it needs liquid water, which is between the temperatures of 0C and 100C. Our experience suggests that this occurs on planets and moons.

Have we found planets? Yup. We’ve got 322 (last I checked) planets orbiting other stars, and those were the ones that were EASY to detect. Those don’t tend to be in the right temperature zone, but if we’ve found 322 in just the last 5-10 years, imagine how many more there must be!

Creating Life:

You need some complex molecules to create even a single-celled organism. Carbon is great for this, because it can easily make form four bonds to other elements. Imagine Legos(TM). You can build anything you want out of Legos(TM), even if all you have is the quintessesntial 8-stud brick, because you can attach pieces together in other ways than just a straight line. When I was in school we also had Unifix Cubes. They were so frustrating, because all you could do was make a long chain. You couldn’t build robots or houses or anything. Carbon is the Lego of the Universe, Helium is the Unifix Cubes. There aren’t many other elements that can be the Lego of the Universe. Silicon is one, but Silicon is significantly less common in the Universe than Carbon. One of my astronomy professors argues strongly against the possibility of Silicon-based life, but I’d like to leave the door open on that one: the Universe is a strange place.

Something More:

We don’t know what it is, but there’s something else that you need to move from a gigantic mass of complex molecules to something “alive.” Is it protection from contamination? Is it the ability to take in and use energy? Scientists are working on this. (Here’s a much better article that reinforces the “moving energy around” idea as what got life going: Why Life Originated.The original link that caused me to say “protection from contamination” is here, though I don’t really like it much.)

So, the first two are easy. The third one we’re not sure about, but People Who Know think it’s a problem for us as humans to figure out, but not too difficult for Nature to stumble across. After all, Nature has a lot of space and a lot of materials, all combining in different ways all the time.

UFOs:

Once you’ve got life, you need to evolve into something intelligent. Then into something that can communicate – that took us millions of years. Then (if you want SETI to succeed) you’ve got to communicate across thousands, hundreds of thousands of lightyears, and stay alive long enough to get a response (this is hard). If you want our UFOs to be of real alien origin then you ALSO need to become spacefaring, travel across thousands, hundreds of thousands of lightyears, (stay alive for that entire journey – which is SUPER-HARD), and arrive at Earth. Hmm.

Earth has only been broadcasting signals into space for 50-100 years. If they’re further than 100 lightyears away, how would they decide to come here? Before we started broadcasting we were nobody. If they’re closer than that, and they can detect radio transmissions, why haven’t we heard their radios? Or, if you want to believe in UFOs, how did they get here so fast? It violates our understanding of Physics, and it doesn’t add up. They do this in Star Trek with fictitious (and awesome) inventions like subspace and warp drive. In Star Wars and Babylon 5 they use hyperspace. In Stargate they use a portal. Fiction. All of them.

When we invent warp drive (real and for true) I’ll eat my words and grant you the possibility that the UFOs really are aliens. Till then, I’m going to say it’s probably the Goodyear Blimp, a bollide, or even a pretty planet.

Who Do You Trust?

Why are you listening to me? I’m not an expert in aliens (who is?). I’ve only seen one UFO in my life (it later became an IFO: the Goodyear Blimp). So then, if I’m not the expert, what did I base this article on?

With the breadth and depth of knowledge now available to the human race, one person can no longer “know everything,” nor can one person understand everything. We are not Erastothsenes, Aristotle, or Plato. We have to trust other people to tell us things. Because of this, we have to choose where we get our information carefully, and everyone will choose different sources as trustworthy.

Me? I trust Carl Sagan and Phil Plait. I also tend to trust Neil DeGrasse Tyson, though I disagree with him on some points of quality education. I like to trust NPR, and I listen to everything Garrison Keillor has to say. I don’t trust Wikipedia to do anything other than jog my memory, point me towards a list of sources, or give me unimportant information (how old is Zac Efron?). I get my tech news from Boing Boing, and my local news and weather from specific blogs (I choose blogs for local information because they know they’re fast, up-to-the-minute, they know they’re biased and admit their bias, and the writers can change their minds and edit things anytime). For current astronomy questions I ask my college profs, re-read my texts, look at the data, and wade through the peer-reviewed papers (if I have time).

Where Did I Get My Info?

Check out what Phil has said about SETI and about UFOs:

Neil DeGrasse Tyson gave a great speech about this to Congress.

How many aliens are there? Figure out your best guess with the Drake Equation.

While I was off gadding about writing grants and training staff … No fewer than FOUR Carnivals went up. Here they are:

Carnival of Space #80 – The Thanksgiving Edition at Starts with a Bang

Carnival of Space #81 – hosted by Tiny Mantras

Carnival of Space #82 – in VIDEO format at Space Disco

and lastly, this week’s (in which I feature at the end, beside Nicole of One Astronomer’s Noise)

Carnival of Space #83 – The Antipodean Edition from Astroblog (in Australia!)

I would like to mention that Nicole’s featured article about the planet found around Fomalhaut is AWESOME. She read the paper, and really explains it to us. She’s analyzing if the paper was done well, and if it really does point towards the splotch of light being a planet or not. You’ll have to go over there to read what she thinks.

Eee-gads. It’s been a long time since I actually wrote for you – I jumped on the NSF-grant-submitting bandwagon, and the deadline is fast approaching. That took priority over AstroInfo for a while, much to my regret. I have a list of topics to address as long as my arm, so let’s start working through them, and hope that I haven’t lost all my readership!

Rainbows

As a birthday present to my brother, let’s talk about how birthday candles are related to rainbows, stars, and astronomers. Get out some rainbow glasses. What? You don’t have any? Well, the stores generally sell a bunch right now for looking at Holiday lights – so pick up a cheap pair at your local … well, it’s unpredictable who will carry them.

Birthday Candles

Play with them. You’ll notice that different lights look different, and give off different rainbows. From a birthday candle you’ll get a smooth, pretty, complete rainbow – maybe some extra yellow. From a fluorescent light you’ll get a couple of single-colored “pictures” of the light you’re looking at. The birthday candle gives you a “black body” spectrum – the whole spectrum of light, released because the candle is hot. From the fluorescent light you’re getting an emission spectrum. DO NOT LOOK AT THE SUN!

What’s Up?

The Lines (the individual colors you see when you look at a fluorescent light):

Electrons. Electrons are jumping around. When energy (light) hits an atom (like the stuff inside the fluorescent light), it excites the electrons. They jump into a higher energy state (go read the first 3 chapters of a chemistry book). When they fall back down they release energy (light). We see that energy as a specific color based on the exact amount released by the electron. The specific electrons of specific atoms release specific colors of light. Always. Therefore we know, every time we see a certain color of red, that it was created by electrons around a Hydrogen atom changing energy states.

The opposite is also true – when the electron jumps up to the higher energy state it absorbs that same specific amount (color) of energy (light). So if we see that only that very specific color of red is missing, we know that the electrons around a Hydrogen atom absorbed that energy.

Each electron can only absorb or release a certain, specific amount of energy. Not a little more or a little less, just that one amount. (Well, you have a few choices, but they’re specific choices).

The Smooth Rainbow:

The “black body” spectrum is just heat energy being released as light. Since there are no electrons jumping, it can release any amount (color) of energy at all, and so it emits them all at once – and you get all colors – a rainbow!

Stars

Now, my colleague Zeta has a really great write-up on this, to which I’ve added a few details.

If the sun is mostly hydrogen and helium, why does sunlight emit the full spectrum of visible light?

Darn good question. Here’s an answer- stick with me, we need to go through a couple steps to get there.

Continuous Spectrum

Ok, our sun has nuclear fusion going on inside of it, and this energy heats the gas our sun is made of to high temperatures. Some of this heated gas turns to light energy, which is the light we see. (in fact, our sun gives off all types of energy of the E-mag spectrum… but the most energy the sun gives is in the visible part of the spectrum, peaking in the “yellow” wavelengths, which is why our sun appears yellow.) All things that are hot give off a visible spectrum, and this is what we see when we put sunlight through a prism. (This is like the birthday candle, but hotter!)

This is called a continuous spectrum, because, well, it’s a continuous strip of colors. This is very similar to what you’d get from a birthday candle, but more complete.

Metallicity

However, part of why we see this continuous spectrum is because our eyes don’t see all the little details that are actually present. If we looked at this spectrum super closely or with cool machines that can tell us the amount of light actually present at each wavelength along the spectrum, we would see something different…

this is the sun’s spectrum actually. See the dark lines? These lines tell us that some elements present in the sun’s atmosphere are actually absorbing energy at certain wavelengths, and the result is “holes” at those wavelengths. (this in fact is called an absorption spectrum, because certain wavelengths are being “absorbed” by gases.)

And by looking at where these black lines are, and what wavelengths they match to, we can tell what gasses are present to cause these absorption lines. This is how we know the sun is mostly H and He. About 3-10 of those lines are the absorption by Hydrogen and Helium. The others are absorption of other elements – because our Sun is a bit “dirty” – it has a large number of different elements, just not very much of each. This is called metallicity. Younger stars have a higher metallicity, because they were made out of the stuff that older stars spewed out into the Universe when they died- Carbon, Iron, Uranium … etc. (Here’s a labeled version of the Solar Spectrum)

Emission Spectrum

In our classes we are showing an emission spectrum of a certain gas, and that is why for H we see this:

Simply put, we don’t see just this emission spectrum for our sun, because our sun is so very hot, and because of that heat a whole visible spectrum is emitted.

Also, astronomers don’t generally use emission spectrums of stars like we see in our lesson- its an oversimplification. Astronomers do study emission spectra, but only in nebulae. Nebulae emit as excited gasses. Maybe stars do, but it doesn’t overpower the black-body spectrum.

Generally, astronomers use the absorption spectrums to see where black lines fall in the spectrum to determine compositions of stars and atmospheres of planets. However, it’s in the lab that astronomers can learn the emission spectrums of certain gasses, when is needed to determine what gasses are showing up in the absorption spectrums they are seeing.

Alice Enevoldsen & Zeta Strickland

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Astronomy Spectrum Homework

P.S. I’m sure that most of you won’t actually read all the way through this one, so I’m writing it as a reference to hand to people when they ask these questions.