21
votes
Why aren't there square astronomical units or square light years?
Such units of area, or something similar, are used.
In particular, they crop up in observations, and the astrophysics of discs, which are essentially 2D objects, where a key observational or physical ...
- 162k
20
votes
Why aren't there any large Ultraviolet (UV) space telescopes?
So... why haven't we launched at least one large, dedicated mid-to-short wavelength UV Space Telescope?
Why dedicated? And why large? Large space telescopes are expensive and compete with other space ...
- 36.3k
11
votes
Why aren't there square astronomical units or square light years?
Area shows up in astronomy, but usually only in terms of portions of the sky as seen from a viewpoint. For example, discussions about telescopes and other detection equipment will often talk about how ...
- 5,247
6
votes
Accepted
Why aren't planets easily visible during daytime?
Planets are visible during the day and most people will have seen Venus prior to sunset or after sunrise.
The calculation you are attempting is flawed because it takes no account of the bright sky ...
- 162k
5
votes
Did the Cold Spot in the CMB help our galaxy to form?
The Cold Spot is radiation emitted from a region that lies 98% of the way to the edge of the observable Universe. With a bit of geometry, you can convince yourself that the fraction of the observable ...
- 39.6k
2
votes
What time of day was the full moon of lunation zero?
I did the same math using Excel: 12/15/2024 21:02 UTC - 1262*29.530588 = 12/4/1922 6:35 UTC.
That would be 6:35 am, not pm.
Depending on what time zone you are in, the link to Calendar-12.com may be ...
- 8,137
1
vote
Why would surface flux include radiation pointing inward the target?
You are not integrating the flux in all directions as indicated in your sketch. The integration is summing up the contributions over all (visible) latitudes and longitudes to the flux in a particular ...
- 162k
1
vote
Surface flux in a specific direction: why is specific intensity in other directions allowed to contribute?
Flux, in terms of power per unit area is in general direction-dependent, unless the radiation is isotropic.
For example, the power emitted by a dipole is zero along its axis and at a maximum for a ...
- 162k
1
vote
Why is there a vector dot product term in the denominator in the definition for specific intensity?
The dot product basically is the projection of one vector onto the other. Using it here allows to take the incident angle into account. E.g. when the Sun is directly at the horizon, the light rays are ...
- 21.4k
1
vote
Accepted
What planets, dwarf planets, and other gravitationally rounded objects can't be seen from Earth at all?
There are no such solar system bodies
There are a few small objects that have been detected by probes, but not seen by Earth-based telescopes, these might include some moonlets embedded in Saturn's ...
- 129k
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