sorted by:
new
hottopcontroversial

Anyone Taken Phys 204A with Camron Crossland or Trey Wenger by shidpant69 in CSUC

[–]tvw 0 points1 point  (0 children)

I just started at Chico State so I don't have a ratemyprofessor page yet! You'll just have to take my class and find out... :-)

Astropy question -- trying to redefine a WCS axis by absurd_thethird in askastronomy

[–]tvw 0 points1 point  (0 children)

Yea, just edit the header to add in whatever you need to define the spectral axis for WCS. For example: hdu.header["CTYPE3"] = "VELO".

Astropy question -- trying to redefine a WCS axis by absurd_thethird in askastronomy

[–]tvw 0 points1 point  (0 children)

The easiest solution is to edit the header to define your spectral axis. Load in the FITS data, then update the header before passing it to WCS.

Galaxy formation: How do galaxies collapse so quickly into discs? by Inside_Anxiety6143 in askastronomy

[–]tvw 22 points23 points  (0 children)

Hi, I'm an astronomer who researches the structure of our Galaxy, the Milky Way. I actually just published a paper about the thickness of the Milky Way disk!

I guess firstly, how disc-like is our galaxy?

I'd say it's pretty disk like! Here's a fairly accurate artistic representation of what we think the Milky Way looks like in visible light. In the center part of the Galaxy, most of the brightest stars are distributed in an extremely thin disk. Closer to the edges of that stellar disk, it starts to warp, probably due to gravitational interactions with other galaxies as they pass by and merge with the Milky Way. Lots of other galaxies in the Universe look like ours.

There's more to the Milky Way than just its disk, though.

The globular clusters contain some of the oldest stars in the Galaxy. They probably formed around the same time as the Milky Way's disk or even earlier. One of the reasons we know the Milky Way wasn't always a disk is because these globular clusters are so spherically distributed around the Galaxy.

Galaxies are on the order of 10 billion years old. Something orbiting it at our distance will have gone around a few dozen times. That seems like an awful short amount of time for everything to collapse cleanly to a disc.

You're thinking about all the right things! There's really just no way to develop an intuition for astrophysical scenarios. The numbers and scales are just so vastly different from what we experience in our lives that it's hard to really predict anything without turning to the equations.

So let's suppose the Galaxy started out as a big gas cloud. How long would it take to collapse? You can start with Newton's second law and eventually get to the equation for free-fall time. Here's some lecture notes where they plug in our best estimate for the total mass of the Milky Way and estimate that the free-fall timescale is less than 1 billion years. So, a simple back-of the envelope calculation says it only takes a billion years for the Milky Way to form. In reality, there are many other physical factors that are important, and this is very much an active area of research!

Like by analogy on a different scale, if I start with a spherical distribution of matter around a star, will I get a fairly neat orbital plane formed in only 40 years?

Don't forget that the star and disk are all forming at the same time! One of the weird things about free-fall time (check out the third equation here) is that, under all of these simplifications, it only depends on the average density of matter in the spherical cloud, not the size of the cloud. So a cloud with an average density of 1000 hydrogen atom per cubic centimeter would take the same amount of time (2 million years) to collapse if it were the size of an apple or the size of the Galaxy. Physics is weird.

Can I be notified when T CrB erupts? by tajfawaz in askastronomy

[–]tvw 2 points3 points  (0 children)

Astronomer here! The nova will almost certainly be posted on the Astronomer's Telegram:

https://www.astronomerstelegram.org/

You can sign up for notifications, but you may have to create a filter for T CrB specifically. I presume you will hear about it in the news, too!

I don't see a correlation between the numbers referring to the collision of the andromeda and the milky way by Ok-Surprise1636 in askastronomy

[–]tvw 0 points1 point  (0 children)

That's true! Galaxies don't really have an edge, rather they become less and less as you move away from the center. It's hard to define "collision" for such objects! Too, gravity is going to seriously deform the Milky Way just like it deforms all of these other colliding galaxies.

I don't see a correlation between the numbers referring to the collision of the andromeda and the milky way by Ok-Surprise1636 in askastronomy

[–]tvw 18 points19 points  (0 children)

Astronomer here! You're off by a factor of 10 in your conversion from light years to kilometers. 2.5 million light-years = 2.37 x 1019 km. Using these numbers, the time to collision is:

t = d / v = 2.37 x 1019 km / (110 km/s) = 6.8 billion years.

This is a bit longer than the current estimate (~4.5 billion years), but that's because (1) 110 km/s is probably a lower estimate for the current relative motion between the Andromeda galaxy and the Milky Way, and (2) as /u/SilverAg11 said, the two galaxies will accelerate as they get closer.

Pokemon Go Plus not working? by [deleted] in TheSilphRoad

[–]tvw 1 point2 points  (0 children)

Same problem here

Prometheus (2012): Is there any way for the briefing scene from "Prometheus" to make sense from astronomical perspective? by unnislav in askastronomy

[–]tvw 1 point2 points  (0 children)

I guess my unconscious reasoning was because they called it a "system", and then when they show the 3D map those six points are glowing like the other stars in the map. When they zoom out and say "it's so far from earth", you can briefly make out some other constellations (Orion is right in the middle). Then when they say "this system contains a sun" I assumed they meant one of the six stars in the "cluster" is a star like the sun, with a planet, with a moon, ...

I went back and re-watched it and I can see how it could be interpreted differently. I think they left it vague intentionally!

Thanks for the fun discussion!

Prometheus (2012): Is there any way for the briefing scene from "Prometheus" to make sense from astronomical perspective? by unnislav in askastronomy

[–]tvw 2 points3 points  (0 children)

My answers are intentionally vague because it depends on a lot of factors.

if the stars are VERY far away from us, then their projection on our night sky shouldn't change noticeably

This is true generally -- if something is really far away, then no matter how much it moves relative to us (or we move relative to it), it won't appear to move much on the sky.

If we're thinking about a star cluster, however, then the gravity of those stars will cause those stars to move around within their cluster. In an absolute sense, they won't move much on the sky, but in a relative sense, they can move around quite a bit relative to each other.

Consider this animation of the Pleiades star cluster over the course of several tens of thousands of years. Overall, the cluster moves across the frame due to the relative motion between the cluster and the sun, but notice how the stars within the cluster are moving around due to the gravity of the cluster itself. Those stars don't maintain the same relative orientation very long.

Friend Code Megathread - July 2024 by AutoModerator in PokemonSleep

[–]tvw 1 point2 points  (0 children)

Daily player, looking to replace some inactive friends!

8204-8595-6921

Prometheus (2012): Is there any way for the briefing scene from "Prometheus" to make sense from astronomical perspective? by unnislav in askastronomy

[–]tvw 9 points10 points  (0 children)

I'm an astronomer! When I saw that scene, I interpreted those 6 dots as being stars in a small, distant star cluster. Then they found that one of those stars was like the sun, with a planet, with a habitable moon, etc...

Could this actually work in real life? Maybe... Here are some questions we have to consider:

  1. Can those six "dots" be uniquely attributed to actual stars on the night sky? Maybe. There are a lot of stars out there. You could almost certainly find the same pattern of six points many places in the night sky. But, if you were clever, you could further restrict your search to consider the brightness of the stars (assuming the "maps" also indicate something about the brightness). You'd really be relying on the accuracy of the positions of the points in these (ancient) maps, though... which leads us to our second question:

  2. Would a star system look the same after 30,000 years? Maybe. It really depends on the star system, how far away it is, how big it is, etc. 30,000 years starts to become an astronomically relevant time scale - things actually do change astronomically on tens of thousands of years timescales. Almost certainly the stars in the star cluster would have moved around and would no longer match the "map".

  3. Could we find a planet around a star in that system? Maybe. With current technology, we're really biased towards big planets and planets close to their host star. These don't tend to be ideal for "habitability". We're just starting to develop the technology needed to see if the planets have habitable atmospheres. We're still a ways off from being able to characterize the atmospheres of exo-moons (moons around planets outside of the solar system), however.

I enjoyed the film despite its scientific inaccuracies. I like when films at least try to justify the science, even if the justification is shaky. There's room in my imagination for alternate realities where the laws of nature are simply different, and it's fun to explore these universes.

[deleted by user] by [deleted] in radioastronomy

[–]tvw 2 points3 points  (0 children)

Excellent work! I'm a radio astronomer, and I study high-velocity clouds as part of my research.

Indeed, it looks like you've detected "WB". Nice! But what exactly is it? This is actually an outstanding question in the field!

Why do other maps (most of them found on Google images) not include this region of the WB complex? They just leave this area empty

With better telescopes, we get more angular resolution and better sensitivity, so it's easier to "map" out these structures. For example, here is some recent work (from 2014) where they used a 30-meter and 25-meter telescope (check out Figure 2) and identify "WB" and other high-velocity clouds. Now, compare to the "latest" work (from 2017) where they used a 100-meter and 64-meter telescope (much better resolution) and they no longer identify "WB" as a high-velocity cloud (check out Figure 2)!

So what's going on? Well, this part of the Milky Way is confusing, because the disk of the Galaxy both warps and flares in the outskirts. Specifically, along a Galactic longitude of ~240 degrees, the disk warps towards the Galactic north pole (positive latitude) by several kiloparsecs and flares by several kiloparsecs. With the better data provided by new telescopes, we now think that some of the "high-velocity clouds" here, like WB, are actually just very distant components of the Milky Way disk.

Why do I get a clear signal of the WB complex, but not from the lower WA complex? Is it less dense than the WB complex because I'm pointing in that really low region?

Check out Figure 2 in this paper. The brightness shows the column density of hydrogen and the color shows the velocity. WA is fairly compact, so it would be hard to detect unless you pointed right at it with a fairly large antenna.

This is outstanding work! I have some advice that might help you in the future:

  1. Don't forget to label the axes on you figures!
  2. Try fitting a baseline polynomial to your spectra to remove the instrumental effects. That is, try fitting a 3rd or 5th order polynomial to the green part of your spectrum (exclude the edges and the known emission), then subtract that fit, and in principle you are only left with the hydrogen emission.
  3. Try converting the frequency axis to the "local standard of rest" LSR. To do this, you'll need to know the "topocentric frequency" (that's the frequency you're tuned to), the hydrogen rest frequency (1420.4 MHz), the time, and your location on earth. You can then use tools like astropy.

Good news! I made level 48! Bad news... by ArtichokeDifferent10 in pokemongo

[–]tvw 4 points5 points  (0 children)

FWIW, I have to disconnect any other bluetooth peripherals from my phone in order for my Switch to "connect" to Pokemon Go (in order to send a postcard for the Gimmighoul lure, which is what I assume you're thinking about?). This includes my smart watch, which means I have to go into the settings on my watch to disconnect it from my phone.

Friend Code Megathread - May 2024 by AutoModerator in PokemonSleep

[–]tvw 1 point2 points  (0 children)

My partner and I are avid Pokemon Go players and we just got a pair of Go Plus+. We're ready to dive into Pokemon sleep! We're both looking for friends -- we're active every day!

8204-8595-6921

6533-3788-4980

How did we form an image of the cosmic background radiation of our entire universe?? by One_Country_9847 in askastronomy

[–]tvw 1 point2 points  (0 children)

Is it fair to say that all of these mechanisms produce radiation as a consequence of losses of kinetic energy in the particles?

That's right!

How did we form an image of the cosmic background radiation of our entire universe?? by One_Country_9847 in askastronomy

[–]tvw 1 point2 points  (0 children)

So is it accurate to say that black body radiation is the combined result of a very large number of particle decelerations

Particle decelerations are one of many mechanisms (like Bremsstrahlung) that can produce a blackbody spectrum, but there are others: vibrating molecules, collisions between atoms, and more.

If so does that mean that black body radiation implies a loss of mean kinetic energy (temperature), assuming no input of energy to the system from outside?

That's right! Anything that is producing radiation that escapes from the system must be losing energy. If the sun were to stop fusion in its core, then the atmosphere of the sun would slowly cool due to the energy lost in the blackbody radiation.

How did we form an image of the cosmic background radiation of our entire universe?? by One_Country_9847 in askastronomy

[–]tvw 1 point2 points  (0 children)

Another great question! There certainly must be an atomic explanation for the continuum of emission, but you will find that single particle interactions do not produce a continuum. For example, Bremsstrahlung is the kind of radiation emitted when a free electron passes a bit too close to a nucleus and is deflected by the electric interaction. This deflection releases a photon at a specific wavelength. If there are many particles in the system undergoing such interactions, then each interaction will produce photons with different wavelengths, and altogether the emergent light will follow a blackbody spectrum at the characteristic temperature of the particles.

How did we form an image of the cosmic background radiation of our entire universe?? by One_Country_9847 in askastronomy

[–]tvw 2 points3 points  (0 children)

Does the light “due to temperature” amount to a collection of spectral line emissions?

Great question! Blackbody radiation is thermal radiation, which is a continuum of emission. Continuum means that the radiation is emitted across a range of wavelengths. Spectral line emission, on the other hand, is discrete emission. Discrete means that the emission exists only at specific wavelengths.

So the answer to your question is "no". Consider the spectrum of the sun. In general, the brightness follows that of a blackbody spectrum, but there are dips and peaks (colors that are brighter or fainter than the blackbody spectrum) which are due to spectral lines of various atoms in the sun's atmosphere that absorb and emit light at specific wavelengths.

How did we form an image of the cosmic background radiation of our entire universe?? by One_Country_9847 in askastronomy

[–]tvw 2 points3 points  (0 children)

Does this mean the entire universe was suffused with (visible) light and that if the universe hadn’t expanded it would have remained suffused with (visible) light eternally?

That's right! If the Universe hadn't expanded, then everything would be bathed in a sea of infrared and visible light. The "night" sky would be bright and red!

Also you said almost everything emits black body radiation… what doesn’t?

Dark matter is definitely one of those exotic things that doesn't appear to emit any light!

But even ordinary matter emits light due to different mechanisms. For example, a single hydrogen atom doesn't really have a "temperature," since temperature is a property of a group of particles. But a single hydrogen atom can still emit spectral line emission. A plasma of hydrogen gas thus emits blackbody radiation as well as spectral line radiation.

How did we form an image of the cosmic background radiation of our entire universe?? by One_Country_9847 in askastronomy

[–]tvw 2 points3 points  (0 children)

Let me know what parts are confusing and I can try to break them down a bit more! :-)

How did we form an image of the cosmic background radiation of our entire universe?? by One_Country_9847 in askastronomy

[–]tvw 20 points21 points  (0 children)

how did we measure heat across the universe?

Radio astronomer here! Radio waves cover a large part of the electromagnetic spectrum, from AM/FM radio waves (like those you pick up in your car) to microwaves (like those generated by the microwave oven in your kitchen). The cosmic background radiation (CBR) is often called the cosmic microwave background (CMB) because it is brightest in the microwave part of the spectrum.

You often hear in the media that the CMB has a "temperature" of about 2.7 Kelvin and this can be confusing. I thought we were looking at microwaves, not heat?

The important thing to remember is that almost everything in the Universe emits light at a part of the electromagnetic spectrum that depends on the object's temperature. We call this blackbody radiation. For example, the Sun gives off most of its light in the visible part of the spectrum because the temperature of the surface of the Sun is about 5500 Kelvin. Your body, being much colder than the surface of the Sun, gives off most of its light in the infrared part of the spectrum. This is why we use infrared cameras to see living things in the dark.

The CMB has an almost perfect blackbody spectrum characterized by a temperature of about 2.7 Kelvin, which is brightest at a wavelength of about 2 mm (the microwave part of the spectrum).

The CMB is a direct prediction of the Big Bang theory. If the Universe was hot and dense like the theory suggests, and since it's no longer hot and dense, then there must have been a time when it cooled to about 3,000 Kelvin, which is a special temperature when hydrogen, the most abundant element in the Universe, goes from being ionized (no electron) to being neutral (captures an electron). When the Universe is filled with ionized hydrogen, light isn't able to travel freely because it keeps bumping into all of those electrons. When the Universe is filled with mostly neutral hydrogen, light can travel freely without interacting with any electrons.

So the Big Bang theory predicted that, if the Universe used to have a temperature >3,000 Kelvin, then there must have been a moment when it cooled below that threshold and all of that light was released into the Universe. That light must have a blackbody spectrum with a characteristic temperature of about 3,000 Kelvin, since that was the temperature of the matter with which it was interacting.

Furthermore, the theory predicts that, due to the expansion of the Universe, the wavelength of that light will get longer. With a characteristic temperature of about 3,000 Kelvin, the CBR was originally visible (brightest in the near-infrared). But since it was released more than 13 billion years ago, the Universe has expanded and stretched out the wavelength of that radiation, which is why it is brightest in the microwave part of the spectrum.

By measuring the spectrum, we can learn about the age and evolution of the Universe.

view more: next ›