# Tag Info

4

Yes it can be seen, given that you do not get much noise and that your sensor is sensitive enough for it to be able to detect the signal. As you have not specified anything about the light not much can be concluded, more than that it depends on the sensor, the transmitter and the noise from everything else.

4

The current data release is DR12. As to how to interact with the data, it depends somewhat on what you want to do. If you have small queries, for instance if you want data for only a handful of objects, there are a couple of web interfaces. If you have larger queries in mind, CASJobs is a good place to start. You'll inevitably need the schema browser to know ...

3

Yes it's possible, and it's called (unsurprisingly) two photon emission. However the probability of two or multi photon emission is generally lower than for single photon emission by several orders of magnitude, so it's hard to observe.

2

I believe (as per John Rennie's answer) that $\mathrm{J}$ in this case does not stand for Joules. The Wikipedia page for the International System of Units (SI) makes a distinction between "unit sybols" (the familiar $\mathrm{m}$ for metres, $\mathrm{J}$ for joules, etc.) and "dimension symbols". The difference is that there are dimension symbols only for ...

2

Spectroscopy: you pass the light through (or reflect from) a dispersive element (a prism or diffraction grating) and then you record the dispersed light. You have a record of the intensity of the light as a function of wavelength. Advantage: potentially you can record the light of one or more objects over a very wide wavelength range and have excellent fine ...

1

From the Wikipedia link you posted, it looks like CIE Standard Illuminant D65 does not exactly model a black body spectrum. Look at the animation in the second figure. The red line is a perfect black body spectrum and the black line is the D65 one. I believe this is because the purpose of D65 is to represent the spectrum of daylight on an average day at ...

1

I don't know much about observational stuff, but since you haven't gotten any answers I thought I would chip in what I could... The error of the raw flux will be based on poisson noise from the signal, and complex read-out/detector noise from your instrument. The latter should be documented by the manufacturer. The former you can calculate based on the ...

1

$\mu_{B}$ is surface brightness of an extended source in the B-band. This is given as (apparent) magnitude per square arc seconds. You need to calculate the area you observe at the distance R through an angle of 1 X 1 arc seconds. With some trigonometry applied you will get; $$A = 4 R^{2} \frac{1 - \cos \varphi}{1 + \cos \varphi}$$ Where the angle is 1''. ...

1

Depending on the shape of the universe the luminosity distance is given by : d_L(z) = \left\{ \begin{array}{rl} \frac{(1 + z) c}{H_0 \sqrt{|\Omega_k|}} \sin \left[ \sqrt{|\Omega_k|} \int _0 ^z \frac{dz'}{H(z')/H_0} \right] & \mbox{for $k = 1$} \\ \frac{(1 + z) c}{H_0} \int _0 ^z \frac{dz'}{H(z')/H_0} & \mbox{for $k = 0$} \\ ...

1

Variables, units and dimensions are fundamentally different concepts. When writing symbols it is conventional to use different fonts to avoid confusion. Quantity symbols (variables) are written in italic font, e.g. $A$. Units are written is upright serif roman font, e.g. $\textrm A$. And Dimensions are written is sans serif roman capital font, e.g. ...

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Better late than never? Yes, what you found in the Matlab package is correct. The luminosity function is the exactly the same curve as the green part of the three XYZ Tristimulus Curves used in modeling human perception of color. Note the XYZ color space is not the same as the RGB color space of a display; XYZ represents the totality of what humans can ...

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