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seen Sep 12 at 7:04

Jul
21
comment Does near light-speed travel doppler-shift the light from the target into gamma rays?
I think that going that fast you should be more worried about the atoms of hydrogen or helium and the grains of dust that you meet than about gamma rays.
Mar
4
reviewed No Action Needed What will happen to life on Earth when Andromeda and Milky Way galaxies collide?
Mar
4
reviewed Close Age of the universe
Mar
4
reviewed Close Black Hole, Object or Portal?
Jan
3
reviewed No Action Needed What Is The Great Attractor?
Jan
2
reviewed Leave Closed What skills would a software developer need to get a job in space research or exploration organization?
Jan
2
reviewed Leave Closed Which planet or moon has all resources that can be used to sustain life in a controlled biosphere?
Dec
20
comment What was the length of year 1 million years back?
@Envite: I don't think that I have an answer. Besides Walter already expanded my comments
Dec
20
comment When is optical refraction important in astronomy?
@astromax: thanks for editing my posts :D
Dec
19
reviewed No Action Needed How does the Milky Way look like above 66° North and below 66° South?
Dec
19
revised When is optical refraction important in astronomy?
add generalisation to my example
Dec
19
comment When is optical refraction important in astronomy?
@AlexeyBobrick. I know that Gravitational lensing is not refraction (that's why I wrote if you allow me), but it's the biggest effect that looks like refraction. I'm searching for some info about interstellar/intergalactic medium refraction, so I'll likely update my answer soon. About "I think that refraction has little/no impact in astronomy": the main reason is that I don't remember any talk/paper/discussion about refraction. And if it were a problem, would be important for cosmology (my field).
Dec
19
comment What can be seen with a 4.5" telescope
Once I've seen Andromeda with a similar telescope: it looks like a cloud as (I think) the telescope is too small to see any structure. The sky was relatively dark.
Dec
18
answered When is optical refraction important in astronomy?
Dec
18
comment What was the length of year 1 million years back?
@AlexanderJanssen: it's complicated for a comment. I wouldn't say the expansion exerts a force. It's more like dragging whatever is in the universe. But when gravitation attraction between two masses becomes strong enough, they begin to disentangle from the expansion and when they reach equilibrium their reciprocal motion becomes (mostly) independent from what happens outside the system (although some parameters of their status might be influenced by the expansion status when they decoupled)
Dec
18
comment When is optical refraction important in astronomy?
you mean refraction in telescopes/instruments or as the light is created and travel towards us?
Dec
18
comment What was the length of year 1 million years back?
I don't think that cosmic expansion has anything to do with changes in the year length. (see comment to the question)
Dec
18
comment What was the length of year 1 million years back?
The solar system (and in fact the Galaxy) is decoupled from cosmic expansion. Any change in the length of the year depends only on local dynamics. Unless the gravitational constant changes with time, but this is an other problem.
Dec
4
comment Find distance from star to star?
That's true if the distance are less than few millions of ligthyears. Otherwise you have to account for cosmological effects and possible cosmic curvature
Nov
2
reviewed No Action Needed Can it be inferred that our cosmological horizon has increased over time?