Hi Reddit!

We are the Ask an Astronomer Team at Cornell University. We are a team of graduate students within the Department of Astronomy that volunteers time to answer questions from the public, both online and in various events hosted throughout the city of Ithaca, NY. Our website describes what we do and how to contact us.

Whenever a popular article is posted about astronomy on Reddit, we notice that a lot of questions float around typically. A few of us have personally tried to answer questions but we thought it might be a good idea to get involved as a team. Answering questions tonight are five students:

Rebecca Harbison - Planetary science, looking at the particle size distribution in the rings of Saturn using data from Cassini.

The Mike Jones - Using HI surveys ALFALFA of the local Universe in order to better understand the local galactic environment.

Michael Lam - Pulsar timing with the NANOGrav collaboration, looking at removing the effects of the interstellar medium on the times-of-arrival of our pulses to help us in the eventual detection of gravitational waves.

Sean Marshall - Radar and infrared observations and shape modeling of near-Earth asteroids.

Tyler Pauly - Astrochemical modeling of protostellar clouds, looking at the formation of complex molecules in low temperature environments.

So please, ask us anything! And thanks to the advertisements on /r/space and /r/AskScience!

EDIT: Hi everyone! I'm going to try to answer a few more and then I'm back to work. We all had a great time doing this and really appreciate you're coming out and asking questions. We'll try to answer some more questions left here over the next day or so feel free to keep posting! -Michael

EDIT July 23 12:52 EDT: This is insane! I will try to be back in a few hours to answer some of the questions, I promise! -Michael

EDIT July 23, 15:08 EDT: I will try to briefly answer some questions for a short while now before coming back on tonight. -Michael

EDIT July 23, 16:04 EDT: I will try to answer a few more relevant questions later tonight. Sorry I can't get to all of them! -Michael

EDIT July 23, 19:55 EDT: Okay, going to answer some last questions. Sorry again if they are brief! -Michael

EDIT July 23, 21:12 EDT: Okay everyone, thank you so much for your questions, thanks to the people who gave good answers as well. We didn't expect it'd get this big and hope to do this again in a few months! -Michael

Comments: 1157 • Responses: 90  • Date: 

LongIslandHK237 karma

Well, since this is an Ask You ANYTHING- What bar are you going to after this AMA, Rulloffs, Chapter House, or Pixel? And have any of you brought a girl up to that Telescope on North Campus or tried to break into Carl Sagan's old house?

CUAskAnAstronomer268 karma

Chapter House is my bar of choice. I've brought about 30 girls to the telescope - all students. No B&E on Sagan's house yet.


tbio25173 karma

Harvard sucks. Go big red!

CUAskAnAstronomer101 karma

We agree! -Michael

Ultraballer2000169 karma

how many space is there?

CUAskAnAstronomer258 karma

All the space. -Rebecca

Stijn25 karma

Isn't it paradoxical that there is both something and nothing inside vacuum? What's your take on this?

CUAskAnAstronomer73 karma

Not really. Vacuum refers to the stuff inhabiting space (or lack thereof), such as mass. A theoretical vacuum contains nothing in that it has nothing like particles, but there is still space, much like you can imagine the "fabric" of spacetime, so I suppose that's something. -Michael

McKennaJames151 karma

Is it taboo to talk about aliens in academic circles?

CUAskAnAstronomer219 karma

Depends on the aliens. Alien visitation of Earth is not taken seriously, since there is no credible evidence. But talk about how we would identify habitable planets (past or present) or places on planets, and what conditions alien life would be found on is quite common in certain circles (Mars, Europa, Enceladus, exoplanetary astronomy). I even know a few astronomers who talk about SETI, but more from a 'how do we do this' (and possibly should we do this).

awesomemanftw137 karma

When new horizons reaches Pluto, what do you expect to see on the surface?

CUAskAnAstronomer271 karma

What we expect on Pluto is based on what we've seen on icy moons around the gas giants (especially Triton, which was captured from the Kuiper Belt, the belt of objects of which Pluto is a member), and based on spectroscopy of the surface.

We know Pluto is covered in ices -- both normal water ice, and methane, nitrogen and carbon monoxide (all gases at room temperature). We also know it has some kind of red material common to the outer solar system, which is likely complex carbon molecules. Finally, we don't have very good maps of the surface, but we know Pluto has a lot of albedo features -- bright and dark spots -- whcih hints that it'll be pretty interesting.

Craters seem like a safe bet, since it's pretty rare for objects in our Solar System to not have at least some. Given that Pluto's thin atmosphere freezes on the surface each winter, the surface is likely to have some erosion (perhaps not much). Triton has ridges and troughs and plateaus from warm ice cracking and moving both at and below the surface, but Pluto is a smaller moon, so it isn't likely to be as active. I hope it does have some geology beyond craters: ridges seem a good bet, since we see them over a lot of icy moons. Geysers -- places where nitrogen is outgassed -- like Triton's would be amazing, but again, it depends on how warm Pluto is inside (which depends on how much rock it started with; rock has nice radioactive elements that keep planets toasty inside). -- Rebecca

Aroundinacircle132 karma

I don't know if this is the right place for this type of question, but here goes.

I read a sci-fi article that claimed that if we search for Earth's reflection in space, we'll be able to actually see into Earth's past and witness history. I think it was something about light travelling for years from Earth to a reflecting surface then back to it.

Is this even remotely possible?

CUAskAnAstronomer273 karma

Yes, this is true, but the reflected light would have to be enormously bright to start with, so this is not practical in practice. However, astronomers did just this with Kepler's Supernova and viewed the "light echo" from the original spuernova bouncing off a distant nebula. -Michael

Carthago_delenda_est61 karma

Because of earthshine, the reflection of light emitted by the Earth that is reflected back to us from the moon, we can technically see 2 seconds back in time.

CUAskAnAstronomer69 karma

Yes, quite true! Though unfortunately, I would think it difficult to look back and see even two seconds into our past. Alas. -Michael

Jkellner07112 karma

If the moon were made of barbecue spare ribs, would you eat it?

CUAskAnAstronomer148 karma

I know I would, and I'd polish it off with a tall, cool Budweiser. -Tyler

CallinInstead87 karma

Have any of you played Kerbal Space Program? What did you think of it?

CUAskAnAstronomer115 karma

We're much better at astronomy than designing and navigating spacecraft, but we have played it. -Michael

We particularly enjoy our launchpad failures. -Mike

Dwaligon85 karma

Hello! I'm hailing you from nearby in Mansfield, PA.

I was wondering about the proposed Thirty Meter Telescope. It boasts that it can produce better quality images than Hubble. In your opinion, is this possible with a land based observatory?

CUAskAnAstronomer225 karma

So usually from the ground you are limited by the Earth's atmosphere. The tubulence in the atmosphere distorts the image and blurs out fine details. However, in the last few decades astronomers have started using something called adaptive optics. Adapative optics is a system whereby the telescope mirror is distorted in real time as you take data. The back of the mirror will have thousands of tiny actuators that flex its surface to focus the light. By focusing on a point source you can effectively eliminate the distortion of the atosphere and recover resolution almost as if you were in space. -Mike

Jupiter_Loves78 karma

What did you guys all major in for your undergrad, and how hopeless would it be to pursue an astronomy related field if I struggle with basic calculus?

I'm a college drop out so feel free to shatter dreams.

CUAskAnAstronomer108 karma

We all majored in physics, with some branching out into astronomy or math. Occasionally some astronomers will also have an engineering background.

I don't mean to shatter dreams by any means, but math is an important part of all of our work. There are astronomy-related jobs that do not require advanced mathematics, related to things like outreach and teaching.


arbitraryentry58 karma

What are the odds on some massive object flinging by earth and sending us drifting toward a slow but inevitable frozen death?

Because I worry about that sometimes.

CUAskAnAstronomer76 karma

Don't worry, the odds aren't high. To an astronomer, "massive object" generally means a star, a stellar remnant (e.g. black hole), or something of comparable mass. Such an object, if passing close to the Sun, would disrupt the planets' orbits and thus render Earth uninhabitable, as you say. We don't know of any nearby stars that are heading straight for us, and such a star would be easy to spot. Black holes are relatively rare, and none is that close. (See http://curious.astro.cornell.edu/question.php?number=473) Black holes don't shine but can be detected indirectly.

Within our Solar System, the main hazard is asteroids. An impact from a large (kilometer-size) near-Earth asteroid could cause global devastation (ask the dinosaurs) but still wouldn't noticeably alter the Earth's orbit. Astronomers monitor asteroids for potential impact threats. See http://neo.jpl.nasa.gov/risk/ for the top impact risks from now through 2199. The greatest known impact risk is asteroid 1950 DA (1.1 km average diameter), which has about one chance in 600 of impacting the Earth in 2880. See http://neo.jpl.nasa.gov/1950da/ for more information on that one. -Sean

onceugoblue23 karma

Ahem, I believe you are referring to the Kaiju come on guys get your facts straight. On a serious note, to what effect will the JWST have on your research?

CUAskAnAstronomer25 karma

We'll be able to resolve the structure of protoplanetary disks, which is pretty important to what I do. -Tyler

Jeff_E_Popp52 karma

Which acapella group should I join? The Harmoniacs or the Do Re Migos?

CUAskAnAstronomer38 karma

Based on extensive youtube video research, my vote goes to the Harmoniacs. Both were enjoyable though! -Tyler

DreamCatcher2451 karma

Hi, thanks for doing this, a few questions:

1)How do you respond to people that say we shouldn't worry about Astronomy research and focus on "more important issues? The way I see it, many space technologies have been adapted for everyday use (e.g. Laser Surgery).

2) In your opinion, what is the most interesting fact about Astronomy that you guys know?

3)What is one potential field of research that we should watch out for in the coming years?

CUAskAnAstronomer74 karma

  1. Fundamental research in all sciences is important because you never know where the next revolutionary invention is going to come from. Also, as you mentioned, things invented for astronomy can be used eslewhere. For example, GPS wouldn't be able to pin point your position to within less that a few hundred metres without Einstein's theory of general relativity.

  2. There are lots of cool things in astronomy, but I think I'll go with - we are all made of stars - literally! All heavy elements, like carbon, oxygen etc. are made in the centre of stars, and that's what makes up our bodies.

  3. Personally I think the next big thing in astronomy will be the new full sky surveys. Large surveys like SDSS, 2MASS and ALFALFA (and many others) are already transforming the way we do astronomy. When LSST comes online and can image the whole sky every few nights, this will surely have a massive impact on our understanding of the Universe.


theyseemescrolling48 karma


CUAskAnAstronomer50 karma

I think that new science from ALMA will be really exciting, as well as hopefully the SKA, and both will give unprecedented views of our Universe (ALMA is currently starting to now and it isn't even completed). Personally, I think that the variety of gravitational wave detectors are going to give us a new window into what's out in the Universe beyond the electromagnetic one (i.e. light) that astronomers have known for thousands of years. -Michael

pand4duck37 karma

Do you have a favorite feature of space?

Do you ever get baffled by the size of space?

How theoretical does your work get?

CUAskAnAstronomer90 karma

I personally am constantly baffled by the size of space, every time you try to compress things by comparing them to smaller things you very quickly get back to a scale you can no longer comprehend. This is why astronomer have to rely so heavily on mathematics, because the scales involved are beyond comprehension by any other means. I study galaxies and to me they are the most beautiful objects in the Universe, they vary so much in shape, size and colour, making up formations that are almost beyond belief. Striving to explain these objects in a fascinating experience.

My work is mainly observation, I have taken, and do use observational data, and I generally work with the large scale statistics of our survey (ALFALFA). -Mike

valjean26034 karma

I want to learn more about astronomy, but I don't know the first thing about it. I love to read though! What book or books would you recommend I start with?

CUAskAnAstronomer71 karma

It all depends on what you're looking to get into! If you are interested in a popular science book, the reddit deity Neil deGrasse Tyson wrote a very engaging book titled Death by Black Hole. I've read it and enjoyed it!

There is also former Cornell Prof. Carl Sagan's book and TV mini-series titled Cosmos, which are also well-loved.

Finally, if you're looking to get into maybe more of the underpinnings of astronomy and astrophysics, the introductory text used here for our Astro 101 course is a good teaching tool. This is it here.

Hope this helps!


averageplease33 karma

My husband is an aspiring astrophotographer. He's got a decent DSLR and a rather smallish telescope, and has been taking photos of M42. What's something else neat he can look at and/or photograph with his current equipment? We're in Seattle, WA if it helps.

CUAskAnAstronomer40 karma

First off, nice job on M42. The Moon is always a nice target, especially near the terminator. I don't know how good your skies are, but you might try for other bright deep-sky objects like M13 and the Ring Nebula. Double stars (like Albireo) with nice color differences might also show up well on film (well pixels). -- Rebecca

Ditto on the Ring Nebula. Also the Whirlpool galaxy. -Michael

averageplease24 karma

Thank you, you guys probably just made his whole week! I will relay those to him post-haste.

CUAskAnAstronomer24 karma

Saturn is always amazing for astrophotography, as is the Moon as well. Enjoy! -Michael

somebitchfelldown33 karma

Thanks for doing this AMA!

So, this might be a dumb question, but I've always wondered. How come we can use the Hubble telescope to see galaxies billions of light years away, but we can't focus on small nearby planets to see if there is life on them?

I always hear about Kepler finding planets in the habitable zone of their stars, so why can't we just focus our telescope and look?

CUAskAnAstronomer53 karma

Well, two reasons. The first is that galaxies are a lot bigger than planets. Our Earth is about 10,000 km across. Our Milky Way is about 100,000 light years across: that's 10,000,000,000,000,000,000 km (that's 15 more zeros). The difference between 10 light years (the nearest planets) and 1 billion light years (far galaxies) is less than the difference in sizes (only 8 zeros there).

The second problem is that planets are next to a really bright thing (their star). Hubble has some special tools to block starlight, giving us fabulous images like Fomalhaut's debris disc and a possible planet, but even that only shows things analogous to where Pluto is in our solar system (and you can see how much light is leaking through in the center). This is why direct detection of even gas giant planets (like Jupiter-size and bigger) is a difficult problem, even for Hubble. Even if we could only see a dim point of light (which is enough to figure out things like 'what is the atmosphere like?'), it is very difficult to see it when it is right next to a much brighter star. Galaxies are easier in comparison, because they are everywhere. -- Rebecca

somebitchfelldown11 karma

Cool, I did not know that! Do you know if we will be able to see these planets in our lifetimes?

CUAskAnAstronomer38 karma

Given the rate at which the science of exoplanet detection and study has increased over the last two decades, I think so! It was pretty hard for astronomers to believe we'd actually directly imaged a planet only five years ago, and now we've directly imaged many. -Michael

InvisibleBlueUnicorn28 karma

Do you guys like 'The Big Bang Theory' sitcom?

CUAskAnAstronomer97 karma

The general consensus is yes, it's pretty funny. The characters are obviously rather cliche examples of scientists, and we feel that the comic book interest is a little over played, and the star trek interest a little under played. -Mike

InvisibleBlueUnicorn21 karma

How much do you guys relate to Sheldon, Leonard, Howard, or Raj?

CUAskAnAstronomer78 karma

We'd like to think we aren't as awkward as any of them, but let's be honest. -Michael

teriyakiterror27 karma

If a tree falls in the woods, will Micheal Lam trip over it on his next run?

CUAskAnAstronomer26 karma

WOW. -Michael

It's a certainty. -Mike

staplerer24 karma

I remember hearing that the signal from pulsars can be used as an interstellar positioning system in much the same way as GPS satellites are used on earth. Pulsars don't transmit their position like GPS satellites, so how would this work? Also, what type of accuracy could be achieved?

CUAskAnAstronomer55 karma

Pulsars act like rapidly-rotating lighthouses. Every time their beam passes by our line-of-sight, we see a blip of light (pulse). The fastest rotating ones spin every few milliseconds. If you had an array of them on the sky, you could triangulate your position in space just by timing when the pulses pass by you and forming a map of where you are, seeing when pulses arrive from a whole bunch of different pulsars. The widths of these pulses are on the order of microseconds, and in one millisecond, light travels approximately 300m. Thus, you can expect an accuracy of several kilometers in position, which matches some of the recent talks I've seen on the subject. -Michael

chaiyaprovo23 karma

What do you think is the best solution to mastering faster-than-light travel, and do you think it is in fact feasible?

Go Big Red!

CUAskAnAstronomer36 karma

The speed of light is the fundamental speed limit that anything can pass through spacetime, but to accelerate something to this speed would take an infinite amount of energy. It is often suggested in sci-fi that wormholes might allow you to circumvent this problem, however if you do the maths you will find that it would actually collapse before anything could get through it. I think it's a much better use of resources to investigate ways to power space crafts more efficiently and ways propel them a higher velocities (less than light). -Mike

passing_white_daisy22 karma

Ithaca is gorges! Did you folk attend Grassroots this year?

CUAskAnAstronomer18 karma

None of the grads answering questions went; we were at the Corning Museum of Glass on Saturday though! It was a pretty neat place.


BigRedBang21 karma

I took Astro last yr & know a few of you were TAs, so I was wondering what you guys did to entertain yourselves when you were grading for 6 hours. Did you like the pictures I drew? It was pretty much the best class ever but I had that hot girl TA so I think Im biased lol

CUAskAnAstronomer27 karma

We typically graded for longer than that.... entertainment involved listening to music, getting annoyed at Mike, and getting some laughs from pictures (you weren't alone!) and some responses. No comments on TAs (except Mike). -Michael

cogitoergovolo20 karma

To any asteroseismology specialists among you: what causes the variations in sounds produced by star vibrations, like here?

What upcoming astronomical events will be visible from Ithaca that we should keep an eye out for?

If you visited my department, I would show you our preserved brain collection. What would you show a visitor to Space Sciences?

CUAskAnAstronomer27 karma

If you have something like a pipe and blow through it, certain frequencies of vibration get amplified enough that you get a nice sound: this is the basic principle of how musical instruments work. Stars have their own vibration frequencies that will get amplified. As for what starts them going, usually just random convection in the star (the same kind of motion you see in a pot of hot water).

As for upcoming events, the Perseid meteor shower (August 11 and 12) is usually nice, and summer is a good time to sit outside and star at the skies, even after midnight (the best time to see meteors).

In addition to the nice prints of Mars and Saturn that we have on our walls, the Space Sciences Building has a number of meteorites on display on our third floor. We also have a (small) radio telescope on our roof, mostly used for teaching purposes, with a control room on the sixth floor. -- Rebecca

genetikiss18 karma

My main childhood dream was to be an astronomer, and now my brother goes to Cornell for mathematics. I wish I could be like you guys. Anyway, how much intrigue and importance is being placed on all these new nearby potentially Earth-like planets? Do you think we'll be making incredible discoveries about them anytime soon?

CUAskAnAstronomer21 karma

It'll be a while before we can know much about Earth-sized and Earth-massed planets in the habitable zone of their stars -- I'll call that a good definition of 'Earth-like'. We'll have a good idea of how common they are and roughly the sizes they are thanks to the Kepler mission (currently down, but has already sent back large amounts of data). Measuring things about their atmospheres will be harder: we are starting to do this with Jupiter-sized planets within the last decade, but Earth-like planets are a lot harder. (Kepler will give us a good list of targets to look at). Perhaps the next generation of instruments will have the ability to separate out some of the planet's light and start to identify ingredients in the atmospheres and actual temperatures.

So I think it depends on what you mean 'incredible'. I think being able to tell how many Earths (and Venuses and Marses) are in the universe is pretty amazing, but the big news of figuring out if any of them have liquid water or oxygen or something will be in the future. -- Rebecca

vestarose17 karma


CUAskAnAstronomer16 karma

It's possible but unlikely. In general, capturing a moon is difficult, and it requires either a non-gravitational force (such as atmospheric drag) or possibly a binary system (in which one object in the binary is captured and the other is thrown off). The upper limit on the size or mass of the satellite would be set by the properties of objects passing near Earth. For instance, the largest potentially hazardous asteroids are around five kilometers in diameter. Since all asteroids and comets that pass near Earth are much smaller than our Moon (whose diameter is about 3500 km), the object would have to appear smaller than the Moon, unless it were fairly large (at least a few kilometers in diameter) and also in a low orbit (just a few hundred kilometers above Earth's surface, like the International Space Station). -Sean

Mel72316 karma

favorite campus library? I was a Mann gal myself.

CUAskAnAstronomer25 karma

I think most of us grads have a nice enough workspace in our office that we rarely get out much, especially to do more work. But when I visit the library, I like Uris the most. It may be a typical response, but the AD White room is pretty enjoyable. -Tyler

Sidzash15 karma

Is Andrew Bernard still working there?

CUAskAnAstronomer22 karma

This is the third Office reference that went straight by all of us.... -Michael

mrkrabz199115 karma

Hi, I don't know if this is your area, but do you guys look for Dyson spheres ever? I know that SETI searches for radio signals (which is a waste of time imo) but I think that finding a dyson sphere would be an amazing find.

CUAskAnAstronomer22 karma

Some astronomers (but not me personally) have indeed looked for signs of Dyson spheres in observational data. For instance, see http://adsabs.harvard.edu/abs/2000bioa.conf..581J and http://adsabs.harvard.edu/abs/2008arXiv0811.2376C -Sean

Minsc_and_Boo_14 karma

I got tons of questions!

  • If you get sucked into a black hole I know you'll not survive but what is this hear about white holes emitting matter or something, and how does all of this tie with wormholes?

  • Seriously, why did they screw over Pluto like that? And what are your favorite planets?

  • Meteor hitting earth. Are we cool or what?

  • What is a nebula? What's in the cloud?

  • What is in the center of a milky way and why is it always portrayed as a gigantic sun of sorts?


CUAskAnAstronomer27 karma

1) White holes exist as mathematical solutions in Einstein's theory of general relativity. They are kind of like the reverse of black holes but there isn't any evidence suggesting that they physically exist. Wormholes are sort of similar in terms of mathematical solutions but again, we don't think they should exist physically.

2) A lot of people feel badly for Pluto, but really, you shouldn't. It's pretty much the first of a new class of object we have defined: dwarf planets. There are a number of dwarf planets in the solar system and they don't fulfill the International Astronomical Union definition of a planet, namely that they do not clear their orbit. But, don't get hung up on the classification, they are still cool objects nonetheless.

3) There's a lot of stuff out there. We don't know of anything going to hit us yet. People (Sean included) look for asteroids and try to figure out their orbits to make sure we're still in the green.

4) A nebula is a cloud of gas. They are primarily made of hydrogren (like everything else in the Universe).

5) A lot of stars are at the center of the Milky Way, but at the very center is a supermassive black hole (roughly 4 million times the mass of our Sun). It's not bright, but it is pretty gigantic!


InvisibleBlueUnicorn14 karma

What's your take on Drake's equation?

CUAskAnAstronomer19 karma

The Drake equation is a very useful way to organise your thoughts on the topic of how many aliens are out there. It nicely orders the relevant parameters, and makes it obvious which ones you do/don't know the value of, and how these values influence the final numer you expect. Astronomers are gradually narrowing down more and more of the parameters of the Drake equation, but there are enough that are virtually completely unknown that it is still possible to use it to derive almost any number of civilisations you want. -Mike

InvisibleBlueUnicorn6 karma

What is your take on the values of different parameters? What do you think is the value of 'N'?

CUAskAnAstronomer13 karma

I think the problem is we just don't know what N is. That's the point. Some of the astronomical parameters (R*, f_p) are being nailed down right now. We could know n_e soon too. But as to the other ones, we can only hypothesize. We don't know enough about our own planet to even answer this one. -Michael

AzBat36013 karma

How's the particle accelerator under the football field?

CUAskAnAstronomer17 karma

Quite large, definitely go and visit if you can. -Michael

Carthago_delenda_est10 karma

If all of the grad students were pitted in a free-for-all death match, who would prevail?

CUAskAnAstronomer32 karma

There's only one way to find out. -Mike

Vertskater10110 karma

Hello! I am planning on becoming an astronomer! I am going to Michigan State studying physics as a major for my bachelors. What would a next step be to become an astronomer? Is a PHD recommended? We are family friends with John Freeman and he is working on the Dark Matter Survey. Just a cool fact! Thanks!

Edit: I understand my grammer doesn't sound like a college student. Very sleep deprived.

CUAskAnAstronomer11 karma

Physics is a great start. A PhD is definitely the way to go but I know a few people who work in astronomy with a master's degree (it is possible with a bachelor's but a lot harder) and do solid research and have published. -Michael

kundalinijunki10 karma

My question concerns ancient astronomy. We always hear about how advanced ancient civilizations were in their knowledge concerning the skies. Does any specific piece of knowledge stand out or amaze you as to how it was known so far back in human history?

CUAskAnAstronomer16 karma

I'm always amazed by the precision with which ancient astronomers studied the skies, such as positions on the sky, the motions of objects, and the ability with which they could predict these motions because they were so accurate. This was true in both western, eastern, and central American astronomy. Also, the ability for people to measure the size of the Earth, the distance to the Moon or the Sun, even if there was a lot of error, was absolutely incredible if you think about it! -Michael

staplerer9 karma

I know that "dark matter" cannot be observed directly, but are there any astronomy experiments being run or conceived to try to observe it indirectly?

CUAskAnAstronomer11 karma

We already have a number of methods to indirectly detect dark matter:

  1. Galaxy rotation curves - Stars in spiral galaxies orbit about the centre. This means that there is mass pulling them towards the centre of the galaxy, and the faster the stars orbit the more mass you need to hold them orbiting in the galaxy (this is also observed for gas as well as stars). We can detect normal matter just by the light it emits or interacts with, and for most galaxies there is simply nowhere near enough mass to hold on to the stars and gas, given how fast they are orbiting. This means that there must be some mass there that we cannot see - i.e dark matter.

  2. Cosmology - All the recent observations constraning our models of cosmology indicate that there isn't enough normal matter in the Universe to explain its expansion history.

  3. Gravitational lensing - Mass bends light, and by measuring how much the light is bent you can measure how much mass is in the 'lens'. Galaxy clusters often act as gravitational lenses. When you add up all the mass in the galaxies, again there just isn't enough to cause the observe bend in the path of the light.

There are also some particle physics type laboratory experiments ongoing here on Earth, but direct observations via astronomy will be quite difficult....

-Mike & Michael

OmarWingNut9 karma

Is a drill mission to the icy oceans of Europa feasible today? If so, what do you expect there to be? Is it really possible there could be multicellular organisms swimming around?

CUAskAnAstronomer11 karma

People have considered such missions, but it's probably not feasible today. Drilling is difficult - stuff tends to break, and if no one is there to fix it you're in trouble. Another idea is to melt through the ice. Either way, a drilling mission like this leads to concerns about about planetary protection.

Tidal heating keeps Europa's interior fairly warm, and spacecraft data indicate that Europa has a salty liquid ocean under its icy crust. So life there seems possible, but we certainly don't know. -Sean

InvisibleBlueUnicorn8 karma

If universe is expanding what will be the fate of Milky-way galaxy in say 20 or 50 billion years?

CUAskAnAstronomer12 karma

We have a post on our website (http://curious.astro.cornell.edu/question.php?number=225) covering what will happen to galaxies as the universe expands. On the other hand, our galaxy is on a collision courses with Andromeda (another large spiral) in 10-odd billion years which will make our galaxy undergo interestesting changes. -- Rebecca

black_sky8 karma

how much time, as an astronomer at a big fancy college, do you spend in front of a computer compared to outside or in front of other equipment?

CUAskAnAstronomer15 karma

I essentially spend all my work time in front of a computer. Even when you go observing you don't look through a telescope, you look at the images in takes on a computer screen; much like a digital camera. Computers have revolutionised most jobs, and astronomy is no different. Having said this, a small sub-set of astronomers build instruments and they will do actual hands-on work. -Mike

black_sky8 karma

If you could answer any question about astronomy/space, what would it be and why?

CUAskAnAstronomer13 karma

Unifying gravity with the other fundamental forces.... it's a big problem for physics and I'd like to know the answer! Or perhaps how the Universe formed. -Michael

The origin of life -Tyler


I know this is cliche but....whats your guys' favorite sci-fi/space related movie?

CUAskAnAstronomer28 karma

Answers from the crowd:

2001: A Space Odyssey - Mike

Galaxy Quest - Michael

Apollo 13 - Rebecca

Star Trek 2: The Wrath of Khan - Sean

Moon or Total Recall - Tyler

BigRedBang7 karma

On a scale from brown dwarf to the material spinning around a supermassive black hole, how hot is Dr. Steve Weldon Squyres? Or if you'd prefer not to say, how sexy is the research he does?

CUAskAnAstronomer30 karma

A scale "from brown dwarf to material spinning around a supermassive black hole" is arbitrary. As scientists, we prefer to use unambiguous numbers. Dr. Squyres is about 310 Kelvin, unless he has a fever. -Sean

TMWNN6 karma

What would you do with the two free NRO telescopes, if you were in charge of deciding on NASA's behalf?

CUAskAnAstronomer8 karma

Unfortunately, the problem with NASA and these two telescopes is all a matter of funding. So, if I were NASA, probably nothing, because funding is a huge problem these days. However, assuming that was not an issue, Hubble itself will no longer undergo any maintenance missions, so we will lose it soon. Even though there are plans to replace it with an even larger telescope (JWST), it would be nice to have "lower" quality science output in the future. One of the most famous images Hubble has taken is the Ultra Deep Field. Having one of them continuously stare into another patch of the sky like the would be awesome! -Michael

InvisibleBlueUnicorn6 karma

Is the Sun second generation or third generation star?

CUAskAnAstronomer7 karma

We don't really know what generation star it is. Stars process hydrogen and helium into heavier elements (what astronomers typically refer to as "metals"). We know based on metallicity it can't be a second generation star. It's tough to say whether there were many short-lived massive stars or slightly longer-lived less massive stars in the billions of years before the Sun was born. -Michael

InvisibleBlueUnicorn4 karma

The metals on earth must have been come from some exploding star/supernova.

If Sun is/may not second/third generation star, then where did the metals on earth came from?

CUAskAnAstronomer10 karma

You are absolutely correct. The metals did come from supernovae. "We are made of star stuff!" -Michael

xeones6 karma

What is your favorite Astronomy Picture of the Day?

CUAskAnAstronomer10 karma

This shows the power of gravitational lensing - http://apod.nasa.gov/apod/ap060524.html -Mike

madRealtor5 karma

"What is" space-time?

How is it on expansion?

CUAskAnAstronomer8 karma

Spacetime is the fundamental 4-dimensional fabric that makes up the Universe. Everything there is is perpetually moving through this fabric, and can never escape it.

All of spacetime was created in the big bang and has been getting stretched out ever since. There isn't enough matter in the Universe for it to halt everything expanding, so this expansion will continue on forever.


InvisibleBlueUnicorn5 karma

Will time machine ever built? at least for the time travels from creation of it onwards?

CUAskAnAstronomer10 karma

This is answered here on our website - http://curious.astro.cornell.edu/question.php?number=270

ArmandTanzarianMusic5 karma

I hope this is still up!

If you had the chance to take that one-way trip to Mars, or for that matter, anywhere else, would you? You would never see Earth again, and likely die on Mars. Similarly, a multi-generational 'ark' where you'd die on the ship but your children would be the conquerors of the new planets, would you volunteer for it?

How feasible do you think asteroid mining (as per the Google founders) is?

And a softball, ever watched/read Contact?

EDIT: And seeing how Sagan will be a recurring theme here, here's Cassini's picture of Earth and the Moon. Insert the appropriate Sagan quote here. http://www.jpl.nasa.gov/news/news.php?release=2013-229#5

CUAskAnAstronomer10 karma

Tyler signed up for Mars One but stopped when they asked for money.

I think asteroid mining is feasible but the technology will still need some development. Technologically, maybe, but economically will be pretty difficult. But, hopefully within the next few years.

A number of us have read/watched Contact, of course!


1dontpanic5 karma

In your opinion, what are the best tools technology wise for cash strapped amature astronomers

CUAskAnAstronomer10 karma

If you're really strapped for cash, a good pair of binoculars and a tripod (if you have weak arms like me) is probably the best thing you can do for the cash. You can get some nice open clusters in those, and views of the Moon. For telescopes, the reflector on a Dobsonian mount is the traditional 'good, but cheap'. (My first 'scope was one of these.) -- Rebecca

Rayc314155 karma

Hi Becca! When you posted this, I thought you would be asking questions, not answering them :P The only astronomy question I've had (could Jupiter's red spot be a moon) got thoroughly debunked the last time I asked it. So how about this...

My college is looking at doing an astronomy 101 course and approached me to see if I could teach it. I've got a Ph.D. in engineering and currently teach physics for them. Do you think I could teach it? If so, what things should I emphasize; and if not, where could we go to find qualified astronomy teachers?

CUAskAnAstronomer13 karma

Sorry, Rebecca has left the scene. All of us in the room have been TAs. I think that you could teach it if you did some background reading in it. It shouldn't be conceptually difficult for someone in your position. I would ask other professors who have taught it at other schools or look at syllabi from other universities' departments. Usually I have seen introductory astronomy broken into two sections: planetary/solar system, and everything else (stars, galaxies, the Universe). Remember that intro astronomy maybe be the only science course students take, since it's typically as a distribution requirement. Teaching them not what we know, but why we know it, and the process of science, is pretty important in making them appreciate it as a whole. -Michael

kelvin1944 karma

Can you explain what types of data is gathered by telescopes?

CUAskAnAstronomer9 karma

Some instruments just take images, like a camera. Other instruments take spectra, which tell us how much energy is emitted or reflected at different wavelengths (for instance, different colors). Some instruments do a combination of these. For more information, see http://curious.astro.cornell.edu/telescopes.php and some its links. -Sean

xCHOWTIMEx4 karma

What's the coolest thing you've witnessed personally?

CUAskAnAstronomer13 karma

The transit of Venus (Venus passed in front of the Sun) was pretty impressive: a little dot that was the size of our Earth showing how big the Sun really is as it slowly moved across (we caught it at sunset here in Ithaca). Also, I visited the Arecibo radio telescope (the largest telescope in the world) and got to climb up to see the instruments, 300 m above the disc. Not recommended for acrophobes. -- Rebecca

Probably standing next to the Green Bank Telescope, the largest steerable object in the world (100m diameter), while it was slewing.... it was so quiet! -Michael

Oaker223 karma

What is a black hole really? Is it possible for you to compare it with something I can even remotely relate to? I am a complete astronomic rookie.

CUAskAnAstronomer6 karma

Absolutely! We have a link here that describes how stellar mass black holes are formed. What they are fundamentally is pretty easy, it's the crazy consequences from their massive gravity that create all sorts of mind-boggling results. -Michael

FukyoShit3 karma

How was Andy as a student?

CUAskAnAstronomer2 karma

Didn't you know he graduated in '95? We may be grad students, but we haven't been here that long! -Michael

CorbinLarryDallas3 karma

Hey guys,

I'm a recent high school graduate with a passion for astronomy/astrophysics. I took all the related classes my school provided, devoured the material and still study on my own when I get time.

The questions no one seemed to answer for me (not guidance counsellors, teachers, anyone) was what the jobs in the field are like, or exactly how to get there. What courses to take in college, where to go and what to do.

So what are your recommendations for a guy who basically aspires to be you?

CUAskAnAstronomer4 karma

Jobs in the field fall primarily into three categories: Teaching, research, and industry. All are gotten there typically by going into higher education in astronomy or a related field and continuing to an advanced degree. When in college, start by taking intro physics and math courses. The astronomy can always come a bit later. -Michael

chubby_brown3 karma

when you wish upon a star, does it matter if it's black or white?

CUAskAnAstronomer5 karma

Well, the stars are there regardless of how bright it is, but they're easier to see when it's dark. - Rebecca

LittleParadiddles3 karma

What is the process involved with determining whether a planet (or moon, or other large body) is suitable for sustaining life?

How do you think the rise of space exploration in the private sector impacts astronomy?

And on a more Earthly level, what advice would you give to undergrads that would like to complete #78 on the list of #161 things to do?

CUAskAnAstronomer3 karma

Many astronomers use the term "habitable zone" - this can mean many things. Generally, we use a simple equation which tells you the temperature something would be, if placed a given distance from its host star. We can then add an additional variable of an atmosphere, which through the greenhouse effect can increase the planet's surface temperature. All of this, though, has only to do with planetary real estate, so to speak. The housing itself may be a bit shoddy - with an atmosphere void of oxygen, we would have a tough time calling it suitable for human life. But because we currently have not detected an atmosphere around a rocky exoplanet, we don't yet differentiate on this.

The private sector space industry is great for publicity, and they can help to launch small craft at lower costs. But when we astronomers get together to launch a multi-billion dollar project based entirely on science, the monetary gain isn't really there for the private sector, so we'll likely still turn to NASA for funding. They may contract out work to the private sector, which means the private sector may still be involved.

As to your last question, I would advise you to wait until the end of the semester, unless that ruins the fun of #78. We the TAs could get in hot water if you don't and we participate. But after the class has ended, no reason not to give it a shot.


LittleParadiddles2 karma

Thanks for the reply!

So, we can tell the temperature of the planet but wouldn't know if the atmosphere contains oxygen? Are there viable solutions on how to effectively "terraform" a planet? (Given we had the resources and means to transport any necessary materials). Sorry if that's a little too sci-fi...

Makes sense about the private/public sector thing. Good to hear that both sides will ultimately benefit astronomy as a whole.

Hah, thanks for the tip about #78.

CUAskAnAstronomer3 karma

The temperature is easier because we can measure the spectrum of light we see. Atmospheres are harder. We only infer the presence of planets around many stars based on their gravitational tug on the stars (the star pulls the planet, but the planet also pulls the star). For some that we see via transits, such as with the Kepler telescope, when the planet crosses in front of the star, you need a really precise spectrum of the star, a really precise spectrum of the star plus the planet, and then you need to subtract the two to get the planet's atmosphere. It's been done for a few gases but it's really tricky to calibrate correctly.

Terraforming is really the realm of sci-fi. Some have suggested types of algae for the oxygen, and then you might need to warm a planet like Mars using greenhouse gases. Not really feasible.... yet. -Michael

omers3 karma

Thanks for doing this and for what you do in general.

I am curious for each of you what is your favourite astronomical object (favourite galaxy, or nebula, etc) and why? If you don't have a favourite object, do you have a favourite Hubble image?

CUAskAnAstronomer5 karma

Some of our answers: Neil Armstrong's footprint on the Moon (courtesy Jason Hofgartner) even if it is not from a telescope, Pale Blue Dot (Cassini's looks awesome, but Voyager's is a classic), the Hubble Ultra Deep Field, Earthrise, the Orion Nebula -Michael

scallywagner2 karma

Reflector or refractor?

CUAskAnAstronomer6 karma

Refractors have a number of significant drawbacks which limit their use to anything but amateur telescopes or historical artifacts. They require flawless glass lenses, which become unfeasible to both form and to hold in place as the size/weight increases. Additionally, light travel through the glass causes chromatic aberration, or color-dependent path differences. Reflectors do not require large lenses, only a reflecting surface. Reflection also doesn't have chromatic aberration issues, so they are the light-focuser of choice.


[deleted]2 karma


RamsesThePigeon2 karma

Given that the comment to which you were responding has been deleted, I'm going to assume that he was asking the following:

"What misconceptions about astronomy do you find the most entertaining?"

Now, for my own question:

Where them aliens be at?

CUAskAnAstronomer9 karma

Unfortunately, not quite.... -Michael

Omicron Persei 8. -Tyler

bloodpressures2 karma

AH! It would be my dream to do an undergraduate REU at Cornell over the summer either with physics or astrophysics. This is awesome, and I hope this question doesn't get buried!

I have a question concerning education. I personally believe it would do the world a lot of good if people could be able to feel the incredible overwhelming 'awe of the universe.' There's a Japanese word for this feeling, Yugen, and is described as "a profound, mysterious sense of the beauty of the universe." As astronomers, I'm guessing that you are familiar with this feeling, and might share the same viewpoint that I do that more people need to experience it.

If you do agree with me, how do you possibly go about conveying it to others? I've tried so many times with friends and family to list the amazing things that are evident about the universe, but it rarely phases them. How do you convince the unamazed to be inspired?

Furthermore, your research projects are totally banging.

CUAskAnAstronomer2 karma

Thanks! Take them outside on a clear night and show them things through binoculars or a telescope. We find that the public loves this. That's how a lot of us got here! -Michael

skunkbutter2 karma

Can you explain what is in the bottom right of this picture?

CUAskAnAstronomer5 karma

It looks like lens flare to me, but who knows. It was taken during the Apollo 8 flight, so there are plenty of surfaces to have a smudge or dust/debris, and good chance of lens flare. Check out the other images taken here.


heykidwannabuysome2 karma

If a massive asteroid were to be discovered today, and we had 24 hours to live, what is the last meal you would want to eat? What's the last show you would watch?

CUAskAnAstronomer6 karma

I haven't thought too much about this before... I guess I would eat a huge breakfast, then a bunch of desserts. And if the world only had 24 hours remaining, I would do other stuff instead of watching TV. -Sean

sjohn13622 karma

Do you listen to Howard Stern?

CUAskAnAstronomer11 karma

No, but we do listen to ourselves talk in our Ask an Astronomer! @ Cornell University Podcastâ„¢.


Bangkok_Dangeresque1 karma

How long has this group been active? I spent 4 years at Cornell and never heard of it, but definitely would've gone to some events if I knew about. What sort of on-campus events do you run?

CUAskAnAstronomer1 karma

Cornell Ask an Astronomer was set up by David Kornreich in 1997. We don't typically have events on campus, but we do have approximately biannual Ask an Astronomer Live events in bars around Ithaca. Our main activities are answering questions via email on our website (http://curious.astro.cornell.edu/index.php), recording podcasts (https://itunes.apple.com/us/podcast/ask-astronomer!-cornell-university/id436026683), and now AMAs.

alecbgreen1 karma

Could you describe the "shape" of the Universe? Is it true it has no center?

CUAskAnAstronomer2 karma

There are three different possibilities for the shape of the Universe, open, closed or flat. These are impossible to correctly visualise as the Universe is 4-dimensional, however a open 2D surface would resemble the shape of a saddle, a closed one whould be like the surface of a ball (never ending, but finite in size), and flat would be just as it sounds.

As far as we have been able to determine thus far our Universe is flat. There is no particular reason to expect this to be the case, but it would naturally arise after a period of inflation in the early Universe, which drives the Universe towards flatness.

It is true that the Universe has no centre. The big bang actually occurred at all points in space, because initially all of space was at one point and have all expanded out since then.


bcastronomer1 karma

I'm about to begin pursuing a degree in Physics (after getting bored with Comp Sci) with a strong emphasis on Astronomy. Any advice you like to give students starting out in the subject?

CUAskAnAstronomer4 karma

I did both computer science and astronomy as an undergraduate. I found both quite interesting, though I appreciate your desire to switch. I'll tell you what one of my professors told me: take as much math as possible. Now, I don't actually believe that, but make sure you have a solid math and physics background. Getting the astronomy on top of that is much easier. If you're starting out, take the intro classes and don't be discouraged if it gets hard. The stuff that you learn later makes it totally worth it. Make sure to work through the problems sincerely (collaboration with people is encouraged). Working through the problems you are given are typically what make you the strongest problem solver. Then, make sure to get involved in research as quickly as possible, even if you don't want to do research later on. My summer experiences were what propelled me to where I am today. -Michael

skalp691 karma


I would like to know about the NASA music CD set Space Sound.

I wonder which part is celestial and which part is human made... For instance, are the tracks sampled? are wave length functions consistent through out the album? or each track?

Also, are the tracks symptomatics of the celestial bodies? ie: could someone recognize celestial bodies by hearing them?

CUAskAnAstronomer1 karma

None of us have heard it; we actually don't know enough about it for a good answer... sorry! -Tyler

hewittpgh1 karma

Which do you prefer: Joe's or ZaZa's?

CUAskAnAstronomer1 karma

ZaZa's is a nicer Italian restaurant but more expensive. I like the gnocchi. -Tyler

KilgoreTroutQQ1 karma

What gets you harder: the thought of sentient life on other planets, or the thought of PUTTING sentient life on other planets?

CUAskAnAstronomer3 karma

My skull remains rigid during all of these thoughts. -Tyler

swimbekoz1 karma

I'm guessing you've all seen this, and hoping you haven't...


Now for the question:

In your best estimation, when will a man/woman walk on Mars?

CUAskAnAstronomer3 karma

2084 -Tyler

2040 -Sean

2060 -Mike

As you can see, it's a great question.... it looks like in the near term it might depend more on private funding. -Michael

blueboybob1 karma

Tyler: Where are your thoughts on PAHs in the interstellar medium? Do you think they show proof that amino acids can form in the ism?

CUAskAnAstronomer1 karma

Unfortunately I do not know nearly enough about PAHs. My work has been focused on modeling reaction networks, at first for simple things like CO, CO2, H2O, etc. Lately, I've been working on a model that is capable of predicting glycine (simplest amino acide) abundance, but the models are not able to go up to PAH sizes - it would be computationally impossible. So for my ignorance of PAHs, I can't say whether they point towards evidence for amino acids. However, I would say that chemical complexity in the warm environments around forming protostars seem to be a prime mixing pot, and finding glycine in a protostellar envelope is something I hope to see or hear about in the next decade. Can you tell me about PAHs? -Tyler

granpa_namstarmonk3y1 karma

why didn't i get into cornell?!

CUAskAnAstronomer2 karma

I think it's getting late... our initial answers are becoming more offensive. -Michael

With a name like namstarmonk3y, what did you expect? -Tyler

Shawn_Jones1 karma

What does the future hold for a Libra?

CUAskAnAstronomer1 karma

Like most constellations, the random motions of the stars will probably break it up in a few hundreds of thousands of years time..... so no more Libra then! -Michael

kbaro9941 karma

Was Astronomy always your thing? If so, when/how did you get into it? If not, what were you doing before that?

I'm a masters student in the humanities, firmly on the barista track, and I regret not pursuing the sciences, basically I'm saying, what are my chances?

CUAskAnAstronomer2 karma

For some of us, the answer is yes. We always wanted to do astronomy and planned it out the whole way, step-by-step. For others, they came to astronomy from other fields in undergraduate. Tyler was a chemical engineer before switching.

As for your chances, I'd say probably the only way would be to start over. But that's if you want to get involved in intense research or something of that sort. Getting involved in astronomy is very easy. Astronomers are big on outreach, and if you can figure out how to get involved that way, I'd say your chances are quite high! -Michael

CivillianTechie1 karma

What are your (collective) personal opinions regarding the probability of us detecting a truly Earth-like planet (similar size, distance from it's star, atmosphere, etc) in the next 10, 25, and 50 years?

What's the biggest next potential discovery you're all salivating over?

CUAskAnAstronomer4 karma

We've detected Earth-size planets currently. We've also detected some this size in roughly the right distance from their star (near the habitable zone). Atmospheres are being worked on now by many people, with a number of confirmed gases. This is pretty tricky, as you might imagine, so even though there's been an enormous amount of progress in the exoplanet field, detecting a truly Earth-like planet will probably take a long time (well over 10 years). With Kepler pretty much dead now, we're going to need new instruments to tackle these problems, and while there are some on the Earth, the loss of Kepler is a huge setback for the community.

As for your other question, there have been a couple of responses to that, but I think immediately relevant will be the discoveries ALMA will make when it is fully online. It's getting there and has already done incredible science. -Michael

Insane921 karma

Most unique astronomical observation any of you have made?

CUAskAnAstronomer3 karma

A lot of us do work on various teams that do some pretty unique stuff! Rebecca does work with Cassini, which is doing really neat stuff around Saturn. Mike and the ALFALFA team are working on a survey of the local Universe in hydrogen (HI) and finding new galaxies even in the local group. Here at Cornell, we've got a number of other unique observations, the most famous probably being Steve Squyres, the Principal Investigator for the Spirit and Opportunity rovers. -Michael

blanconejo1 karma

What kind of music do y'all enjoy while uncovering the secrets of existence?

CUAskAnAstronomer2 karma

Depends on my mood, sometimes classical, sometimes pop, sometimes oldies. -Sean

I've definitely had The Dark Knight trilogy on loop while observing recently, but soundtracks are always great as background working music. Have also gotten into electroswing recently. -Michael

This -Mike

Secrets of existence require ambient/post-rock/electronica. I'm partial to Boards of Canada, God is an Astronaut, Com Truise and Kuedo. Also, disregard all of Mike's answers -Tyler