Archive for the ‘AstroInfo Article’ Category

Oops. We’ve been teaching meteors wrong. I’ll bet it’s my fault.

The Short:

Meteors do not heat up due to friction with the atmosphere, unlike what our classic hand-rubbing demonstration leads you to believe. They heat up due to compression of the atmosphere. Mostly.

The Story:

So imagine a boat speeding across Lake Washington. See that bow shock, the beginning of the wake, which forms in front of your imaginary boat? That’s kinda what’s happening. Of course, water doesn’t compress (being a liquid), so you get up-and-down waves in water instead of compressed density waves, but gas like an atmosphere is VERY good at compressing, so for our meteor we’ll get nice compression. The speeding meteor-particle (yes, the tiny sand-sized piece of rock) compresses the air in front of it, like the boat’s bow shock.

Density Waves:

We talked about density waves a little while ago when we were discussion the galaxy. Instead of up-down or side-to-side waves, density waves are just more stuff or less stuff in a given area. In the case of compression heating, we’re squishing more stuff (air) into a smaller area.

Compression Heating:

When you compress a gas it heats up. Well, almost always. There are some weird cases, but this isn’t one of them. This is classic PV=nRT. What?! Am I allowed to write that on the internet? Yes. This is one of the things you learn early on in a chemistry class that has even a little math in it. Basically the Pressure and Volume of a gas are directly related (=) to the number of atoms, R (just a number), and Temperature. So, if you change one of those things, the others have to change too… oh, and you can’t change n or R.

Alice, I’m not listening anymore:

Okay, come back. This is why a bicycle pump heats up when you’re pumping. It’s not the friction of the little thing inside, it’s that you’re pressurizing gas. This is why aerosol cans (shaving cream, hairspray, those compressed air cans you get for dusting out your computer) cool off when you use them.

The New Way:

You can still do hand-rubbing. Until we come up with a kinesthetic way to teach compression (suggestions?), you might as well – we’re still talking about heat, and that’s a great demonstration of heat. Just mention that it’s not friction that burns up the meteor – it’s compression heating (like a cooling aerosol can).

Alice Enevoldsen

Want More?

Thanks for tipping me off Phil.

Here’s some more from NASA.

Lookie!

Wow. BBC – huh. Their date for that clip is November 08. Well, that video of me is from … either _early_ 2008 or back in 2007 … or was it before that? I don’t remember – it wasn’t the November 08 or the ephemeral “recent” one – I didn’t report on either of those, but my clip got picked up for the one in November.

Especially since I was in FLORIDA enjoying the SUN when this happened…

Though it wasn’t before May of 07, because that’s how long my hair’s been blue!

Yay for becoming international!

Tip o the video camera to Phil Plait!

Scientists detected methane in Mars’s atmosphere. In fact, they’ve been detecting it for years. Methane should dissipate from the atmosphere in that time, but it didn’t. This means something on Mars is creating more methane. There are two giant ways to make methane:

1) Life (you know, even at the cellular level)
2) Geology (chemical reaction)

Either one of these is cool. We know there is a little geologically happening on Mars, but it seems fairly dead. Finding methane means that there are chemical processes going on.

It does NOT mean there is life on Mars. It could, but it’s WAAAAY more likely to be geology.

Read more from Emily.

Our universe is not only expanding – but that expansion is accelerating. It’s expanding faster and faster and faster. When you’re driving your car you don’t speed up for no reason – either you step on the gas, you’re rolling down a hill, you get slammed from behind, or your engine suddenly and unexpectedly starts feeding gas to the engine (I hope not!). The universe’s expansion can’t speed up for no reason either. That energy MUST come from somewhere – but we don’t know where, so we’re calling this extra energy “Dark Energy.”

Law of the Universe:

You cannot create energy from nothing. Just like you wouldn’t expect to see a kitten materialize out of nothingness and appear on your keyboard (it might jump there, but not materialize!), you can’t get energy out of nothing. It all comes from somewhere. This is called the law of conservation of energy. Sometimes it’s called the first law of thermodynamics.

The Universe is Accelerating:

From our measurements of Type 1a supernovae we know that the universe is expanding and that expansion is accelerating. Basically, those supernovae are farther away than our physics models predict them to be, and there’s not enough energy in the Universe to do that.

Cosmological Constant:

Einstein proposed a “cosmological constant” to solve a similar problem many years ago. Then he changed his mind and gave it up. With our new observations, it’s back in play now. Under this hypothesis, a specific volume of space (the cosmos) always (constantly) has a given amount of energy in it. Say you had one cubic meter of space. Under this theory, it would have … let’s say an amount “5” of energy. Then, over time the universe expands and now, your one cubic meter of space now takes up two cubic meters. Because of the cosmological constant, that space would have an amount “10” of energy. By definition. Just because it is space. (Usually we do this with variables in astronomy, but I wanted to be clear). Pretty weird, but you get lots of extra energy.

Quintessence:

What if Dark Energy is not constant? What if it changes over space and time? You’ve got a little more here, a little less there. There was more last year than there will be in a billion years. That’s the quintessence hypothesis. Maybe it’s particles (like photons and electrons), or maybe it’s a field (like the magnetic field of the Earth), but in any case it changes, it’s not constant.

New Physics:

And, not to be forgotten, what if our equations for Physics are just wrong? What if we need to completely rethink them? In any case, the universe is accelerating in its expansion, so until we know what is making it do that, we’re just going to call it Dark Energy.

P.S. Ghosts are not made of Dark Energy. That’s crazy talk.

Want More?

Pamela Gay “Dark Energy is Real”
Ethan Siegel
Astronomy Cast and 365 Days of Astronomy
Sky and Telescope, February 2009 “Going over the Dark Side” – More Info

Alice Enevoldsen

#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.!!