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Jul
24
accepted Speed of blast from supernova
Jul
22
asked Speed of blast from supernova
Jul
21
comment Was the Universe expanding before the beginning of inflation?
@LocalFluff Since the universe extends beyond the 15 Mly visual range, we don't know what the boundary is; it could be curved to close the universe, or it could be an impregnable wall. So the universe might have a size; we just don't know for certain yet.
Jul
20
comment Was the Universe expanding before the beginning of inflation?
@LocalFluff It's true that the "visible universe" is no larger than light travel time distance, but the universe can easily be larger than that. See pages.uoregon.edu/jimbrau/BrauImNew/Chap27/7th/…
Jul
19
comment Was the Universe expanding before the beginning of inflation?
The current theory of inflation has the universe at a radius of 15 Mpc after $10^{-34}$ sec. Does it really matter if the universe was slowly expanding after creation and before the inflation? How long could the period possible be if the inflation took most of the time?
Jul
18
comment Does Pluto have impact craters?
Rob, what we are seeing is that there are no small ones. I disagree with that; after all, Pluto is 1/3 the size of the moon and the craters (on Pluto) would be about the size of the smallest craters on the moon.
Jul
13
comment How many planets are there in this solar system?
You can add more dwarf planets: Sedna, Ixion, Orcus, Quaoar, and Varuna. There may be more as well.
Jul
13
reviewed Approve How many planets are there in this solar system?
Jul
11
reviewed Close How small would you have to crush an object for it to become a black hole?
Jul
11
reviewed Close Can we spot a gray-goo exoplanet?
Jul
7
comment How clearly would I be able to see a galaxy with the naked eye if viewed from a “close” distance?
OK, for 90° field of view $tan(45°)=\frac {500,000,000,000,000,000}{d}$ or $d=\frac {500,000,000,000,000,000}{tan(45°)}$, $d=500,000,000,000,000,000\ km$. I don't know what sort of resolution you would get, nor how bright the galaxy would be.
Jul
5
comment How clearly would I be able to see a galaxy with the naked eye if viewed from a “close” distance?
The Milky Way is about 1,000,000,000,000,000,000 km across. From 1,000,000 km away from the edge, it will almost stretch 180°. I would say that most of the nearby stars would be distinguishable and due to the density near the edge, they would overlap.
Jul
2
comment Eclipse on the moon
The sun is large, and yet a small moon (relatively speaking) covers it entirely. Now the shadow casts by the moon lands on the Earth (which is larger than the moon). It makes sense to me that the shadow is smaller than the Earth, even though the moon hides the sun. It all depends on where you are. 500 miles south from the location of a total eclipse, may not have the moon hiding even touching the sun.
Jul
2
comment Eclipse on the moon
How else would the moon block the sun?
Jul
2
comment Eclipse on the moon
Have you seen the map of the moon's shadow track across the Earth when there is a solar eclipse? eclipse.gsfc.nasa.gov/SEmono/TSE2017/TSE2017fig/TSE2017-usa.jpg
Jun
27
reviewed Close What to do after first year of amateur astronomy?
Jun
27
reviewed Approve Are space telescopes completely out of the earth's atmosphere?
Jun
26
comment Why is the moon a fuzzy, white ball?
Do you wear glasses? Did you remove your glasses to view through the scope?
Jun
24
reviewed No Action Needed Is the Milky Way Visible from Nebraska?
Jun
24
reviewed Approve Does Sun have a reflection on Earth?