# Tag Info

2

That question made me curious too! The grazing can be quantified with the impact parameter b, easy to understand in this schematic from Winn 2011. When looking at exoplanet.eu diagrams with one axis set as the "Impact Parameter b", some planets show as having b~1.7 and 1.6, however these are from TTV (Transit-timing variation) measurements. I'm ...

2

I first wanted to edit this into my other answer here, but since this, even though being highly relevant for the issue, does not directly address the OP's question(s), I decided to add this as a separate answer : The orbital elements used in the cited work for simulating the orbit of the Eagle ascent stage after being jettisoned from Apollo 11 are actually ...

5

According to Formation of the UV Spectrum of Molecular Hydrogen in the Sun (S. A. Jaeggli et al. 2018 ApJ 855 134, also here) molecular hydrogen in the sun was first spectroscopically discovered in 1977. The model calculation in this reference give a ratio molecular/atomic hydrogen of around $10^{-5}$ at a height of about 650 km (where the $H_2$ emissions ...

7

When you consider an expanding universe, the meaning of "distance" becomes difficult, and different reporters use different definitions. In many newspapers the distance used is the "light travel time distance". This is the time that light has been travelling from the galaxy multiplied by the speed of light. So a galaxy that is 300 million ...

1

Spectral wavelengths usually are defined as vacuum wavelength. The index of refraction of the medium influences the wavelength, and as such 'in vacuum' is both easier to define and measure: You'd need to define and specify composition, pressure and temperature in addition to the wavelength for each measurement in air - all of which is unnecessary if you ...

1

The peaks in the temperature and polarization spectra determine the angular size of the sound horizon at the time of recombination fairly accurately: $$\theta = \frac{r}{D(z)}$$ The sound horizon, which is represented by r, is the comoving distance a sound wave could travel from the beginning of the universe to recombination and is a standard ruler is any ...

0

I think I have an answer to my question. This website seems to explain it best: How to measure the color terms for your camera If we measure a variety of standard stars (bluer and redder stars) using b and v magnitudes, we can compare them to the what their magnitudes should be using the following equation: m_instrumental - m_B = C_B (B-V) + ZP We can plot ...

7

Right ascension is usually given in hours, minutes and seconds, but declination is usually given in degrees, arcminutes (') and arcseconds ("), with one arcminute being 1/60th of a degree and one arcsecond being 1/60th of an arcminute. This means that the declination of the source you list should be 40$^{\circ}$08"55.6', in accordance with the SDSS ...

1

Arrive whithin a year = almost surely already within the heliosphere. I assume a stellar remnant black hole (bigger ones will be even more noticeable, smaller ones are still unknown). It will be a rather bright shiny x-ray source in the sky (we do have enough matter around to support a bright accretion disk). It will distort our outer planet's orbits for ...

1

A black hole approaching our solar system would have been detected hundred of years in advance due to nearby stars shifting position, although it's true nature wouldn't be known until decades ago, when the concept of black holes was first postulated and then confirmed. Even if the black hole were to enter the solar system, rather then pass nearby it, it ...

0

To determine the orbit of any body around the sun, at least three observations are needed at different times. This is true for black holes as much as it is true for asteroids or comets. With three accurate observations at three different times, a Keplarian orbit can be fitted. The trouble with microlensing is that you only get a single observation. Even ...

6

There are really two type of "dark matter" in the universe and two "dark matter problems". The first problem is that most of the "normal matter" in the universe is dark and difficult to find (a.k.a. the missing baryon problem). This dark matter could consist of gas between galaxies (most likely) or in the form of objects that ...

1

I can partially answer this from a pulsar perspective. Across the board, parallax measurements are a fairly new development in radio astronomy. Interferometers are required to attain any reasonable degree in accuracy, and so parallax measurements have come into play mainly in the last two decades, with instruments like the Very Long Baseline Array taking ...

1

Here is a brief explanation of the various techniques that can be used to detect exoplanets. The scatter plot suggests that for a planet to be detected by direct imaging, it has to have (roughly speaking) an orbit as large as Jupiter's, and a mass as great as Jupiter's. So Jupiter looks like the best candidate. As for your second question, the declination of ...

0

Let's pretend we have a mirror in the shape of a spherical cap, with dimensions the same as JWST: diameter d=6.5m and radius of curvature r=15.88m. Then the distance along the surface of the mirror between two opposite points on its rim is given by 2r arcsin (d/2r), which comes to about 6.546m. This is only about 0.7% longer than the straight-line distance d....

7

Background/Video Starting around minute 6 of the video frozen orbits are discussed, and some example GMAT simulations are run to explain how lunar orbits can be simulated including up to order 160 in the Moon's gravitational spherical harmonics, which have been very accurately mapped by the GRAIL mission. The video then links to the study itself: arXiv: ...

6

There are a couple of inconsistencies with theory presented in the video and the paper it is based on. Apparently, the author(s) are suggesting that Eagle did not crash as it was/is in a 'frozen' orbit. However, frozen orbits are thought to occur only for orbits with higher inclinations (in fact only for 4 specific inclinations: 27,50,76 and 86 deg) (see ...

3

You are asking about the Moon's diurnal libration. While it is small (about 1°), it is easily measurable. It is also overwhelmed by the much larger librations due to the Moon's non-circular orbit and due to the Moon's orbit being inclined with respect to the Earth's equatorial plane.

3

Sources above: https://www.facebook.com/NASAWebb/photos/10158883840795049/ below: https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-telescope Do telescope measurements (in meters, usually) measure in a straight line, from edge to edge, or follow the curve of the mirror? The short answer is @JamesK's; it's the straight-line diameter of whatever ...

4

Straight line, though it wont make much difference, The point about the size is that it tells you about how much light the telescope can gather. This is the "projected-flat" area, not the curved surface area. However, the difference is not much, as telescope mirrors are not highly curved. I suppose it makes more of a difference when considering ...

3

You'd be completely right that a single Fourier transform would be needed if the interferometer were able to sample the entire $(u,v)$ plane. Unfortunately, that's not the case; we only have a fairly small, finite number of dishes and a finite amount of time. Coverage of the plane will increase as time passes and the Earth rotates, but it's going to be ...

3

The closest that I know of would either be Nightwatch (Terence Dickinson) and/or The Backyard Astronomer's Guide (also Terence Dickinson). I don't think either of those cover your last requirement of "telescopes of all regions of the EM spectrum like Ultraviolet Telescopes, Infrared Telescopes, etc.", though.

2

The surface brightness of a source is by definition the flux density per solid angle; the surface brightness sensitivity of a telescope is, analogously, its point source sensitivity divided by the beam solid angle.$^{\dagger}$ Interferometers have smaller beam solid angles than dishes with the same area (Frayer 2017). Given that the solid angle is $\Omega\... 3 Both statements are correct: aperture is the most important factor, and many large aperture telescopes are resold due to lack of use. The brightness of any object you observe is determined by the aperture of the telescope ("light grasp"). With larger objects, such as planets, the aperture also determines the resolution: the amount of detail you're ... 7 In Observing Handbook and Catalogue of Deep-Sky Objects, Luginbuhl and Skiff describe how hundreds of deep-sky objects look in different apertures. For example, for galaxy M63 (NGC 5055) in Canes Venatici: Messier 63 is an easy object for 6 cm, located 3'.5 E and a bit S of a mag. 8.5 star. It is elongated E-W, passing just S of the star. The broadly ... 5 Some of the comments here seem to be suggesting that there should not be any residual charge of the Sun at all because of the fact that in a conducting medium no electric fields can exist. This argument ignores the crucial point here, namely that there are unequal numbers of positive and negative charges, because electrons, unlike ions, can easily escape ... 4 It seems that the planet is marked with longitudinal lines every 10 degrees, and so you can measure off the video that the planet rotates by about a little less than three longitudinal lines, or about 30 degrees. As Jupiter has a rotation period of just under 10 hours, the length of time can be estimated as about 10×30/360 hours: 50 minutes, or possibly ... 8 Bond et al. (2017) measure the orbital period of the Sirius system to be$50.1284 \pm 0.0043$years. I believe this is the most precise and accurate value (I cannot find any more recent papers, with new determinations, that cite this paper). An earlier, comprehensive study by Gatewood & Gatewood (1978) gave$50.090\pm 0.056\$ years; consistent with the ...

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Calculations like this one for the orbital period of a binary system are hardly ever done analytically. Astronomers usually take some known approximations and extend it to system like Sirius, and get an estimate for their period numerically (and a good one, by the looks of it). If you're curious, we can derive this version of the 3rd law by considering the ...

5

I was wondering why the absorbtion lines of the template are broader then those of the galaxy, since it actually should be the other way arround. You are correct that it should be the other way around. The reason the plot looks confusing is that you are not actually plotting the galaxy spectrum in the top panel; you are plotting some combination of noise ...

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