I recently read an article online stating that electromagnetic radiation is 'a form of energy emitted and absorbed by charged particles'.
This isn't always correct, is it? I mean, I know that charged particles that are accelerating can emit bremsstrahlung and synchrotron radiation, but my own...
Some PC- based astronomy packages such as Redshift will calculate this automatically for you, for any start date and end date you choose. Conjunctions such as this are relatively common, and the two planets aren't especially close together this time around. The nice thing about this particular...
Hi all,
Does the age we assign to the Universe depend on how we define distances in space? I've read that there are a whole host of ways that cosmologists can define distance in the Universe, and that no particular way is *correct* as such.
Another factor is that General Relativity implies...
As I understand it, the first 'rung' on the ladder would be finding the distance to Venus at greatest elongation using radar-ranging, which is an absolute measure (I think). Then we use some basic trigonometry to find the Earth's distance to the Sun, which could then be used to calibrate stellar...
I thought my solution seemed a bit too simple!
But I've had another thought: isn't the important issue that the redshift-distance measurement scale is a reasonable measure of *relative* distance rather than *absolute* distance, because the scale is calibrated using other 'rungs' on the...
I understand that a Hubble diagram is a graph of recession velocity plotted against distance for distant galaxies, and shows a linear relationship. The Hubble constant is the gradient of the graph.
We are now observing extremely distant galaxies with greater than expected velocities due to...
Thanks for everyone's feedback on this, I've found it really interesting. I think I've sorted out my initial misconception.
Okay, here goes...
I take the spectrum of a galaxy and observe its redshift. Using the Hubble Relation, I calculate the galaxy's distance to be ten billion light...
So using this normal distance measure, if I observed a galaxy to be five billion light years away using the supernova method, then I would say that it was *actually* five billion light years away at this present time. Is that correct?
Thanks for your replies...I'm still a bit hazy on this, I'm afraid.
I think part of my problem is that I'm imagining the redshift of a galaxy to be produced by a 'police siren' type Doppler Shift rather than a cosmological redshift. They aren't the same thing, are they?
Am I right in saying...
Hi all, this is my first post; apologies if it seems a bit basic, I suspect there's something fundamental I'm not getting here :smile:
Say I observe the spectrum of a galaxy, and I calculate its redshift. I then use the Hubble Relation to find its distance, which is, say, ten billion light...