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seen Mar 29 at 18:38

Mar
26
answered Do we still use the term “astronomical unit” nowadays?
Feb
23
comment Fourier Transform of Galaxy Images
I'm not sure what you're question is? Why have you chosen to use fourier transform for segmentation? If I look at the bottom picture, the fourier transform does not seem to be a very good feature.
Feb
10
reviewed Approve L4&L5 positions?
Feb
9
answered Is it proper to refer to objects beyond Neptune as “Kuiper Belt Objects?”
Feb
2
comment Mass, Radius, Colour, Size, Type of a Star from the Hipparcos Catalog
The value for the temperature $4000\textrm{K}$ was read from a graph so it is very imprecise. There are some empirical relations that transform colour index to temperature but they depend on the type of star. They can be found in the scientific literature and they will often involve transforming the colour index used in Hipparcos to other passbands (such as those used by SDSS).
Feb
2
comment Mass, Radius, Colour, Size, Type of a Star from the Hipparcos Catalog
To calculate $L$ you will need the apparent (V) magnitude $m_V$ and the parallax to calculate first the distance (first equation above, and don't forget that Hipparcos gives the parallax in MILLIarcseconds) and then the absolute magnitude $M$ (second equation above). Together with the absolute magnitude of the Sun ($M_{\textrm{sun}}$ = 4.83) you can calculate the Luminosity with $L = 10^{M-M_{\textrm{sun}}}$. This is expressed in Solar Luminosities, i.e. the Sun will have a luminosity of $L=1.0 L_{\textrm{sun}}$. (The SI unit is Watt = Joule per second.)
Feb
1
comment Mass, Radius, Colour, Size, Type of a Star from the Hipparcos Catalog
First: Yes $-2.5\log(L/L_{\textrm{sun}})$ is $-2.5\times \log()$. As to converting this into computer code, I'm not sure what you do not understand. Maybe the conversion from $M-M_{\textrm{sun}} = \log{\frac{L}{L_{\textrm{sun}}}}$? This would become $\frac{L}{L_{\textrm{sun}}} = 10^{M-M_{\textrm{sun}}}$ so if you have a value for $M-M_{\textrm{sun}}$, say $2.056$, then you can calculate the luminosity (in solar luminosities) with 'pow(10,2.056)'.
Feb
1
answered Mass, Radius, Colour, Size, Type of a Star from the Hipparcos Catalog
Jan
28
comment Retrograde motion and Kuiper Belt Objects
To add to my comment: astronomical twilight is defined when the Sun is 18 degree below the horizon. If the Sun is lower than that, observations should be possible from a site that is dark enough. When the KBO a starts or ends its prograde motion the angle is 90 degrees. That should be enough.
Jan
28
comment Retrograde motion and Kuiper Belt Objects
Good point, the prograde motion of an object infinitely far away will take 6 months. And it will occur when the Earth is on the half of its orbit that is opposite to the KBO. That is when the KBO will be most difficult to observe. The worst circumstances will be when the KBO is exactly on the ecliptic. But even then it will still be observable when it just starts the prograde motion or when it is about to end the prograde motion. At least from somewhere on the Earth, for instance, one of the poles. At that point the angle KBO-Earth-Sun will be about 90 degrees.
Jan
28
answered Retrograde motion and Kuiper Belt Objects
Jan
27
comment How to complete the Hipparcos Catalog?
I'm afraid not. I've been thinking about compiling the list myself, but never got around to it. If you are satisfied with only the MOST common names (in English, i.e. not in arabian or greek lettering) then you might consider compiling the list yourself. There are not that many stars that have common names that are used. -- Most constellations will have only a few (one or two) stars whose names are actually used. In the southern hemisphere most constellations will have 0 stars with common names (where the Bayer name is most often used).
Jan
26
comment What are the units of distance in this subtended angle calculation?
Yes, but the question was not on how to convert between arc seconds and radians, @user193041 already did that correctly in the question.
Jan
25
answered How to complete the Hipparcos Catalog?
Jan
24
awarded  Yearling
Jan
22
awarded  Critic
Jan
22
comment What are the units of distance in this subtended angle calculation?
There are actually quite a lot of dimensionless units. And they are real units. Another dimensionless unit is for instance Magnitude (as a unit not a measurement scale).
Jan
22
comment What are the units of distance in this subtended angle calculation?
But @user193041 already did convert the angle in arc seconds to radians. This is not an answer to the question.
Jan
16
reviewed Approve Is it safe to view moon at daytime through telescope
Jan
15
revised Is the universe simply a mass of atoms in 'void'; what does it look like?
added 92 characters in body