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1

From the book Turn Left at Orion by Guy Consolmagno and Dan M. Davis, Galileo might have set his beard on fire with a telescope pointed at the Sun. And you must keep your eyes -- and your clothing -- out of the path of the projected light. It is said that Galileo set fire to his beard doing this! In his defense, he was the first person to look at the Sun ...


16

If you measure the gravitational waveform from an inspiralling binary, you can at any point measure the amplitude, instantaneous frequency and the rate of change of frequency. The last two give you the "chirp mass", which is related to the product and sum of the binary component masses. The amplitude of the gravitational wave then depends on the chirp mass ...


5

So the Hipparchos parallax of Betelgeuse doesn't seem accurate enough? If only someone would launch an even more advanced astrometric satellite than Hipparchos. Actually the ESA has launched an even more advanced astrometric satellite, Gaia, expected to operate from 2013 to about 2022. And it is possible that Gaia has already produced more accurate ...


8

The problem is that the apparent diameter of Betelguese is about 50 mas (milli arc seconds --- 1 mas is about 5 nano-radians) while its parallax is about 5 mas and its shape and surface brightness are both irregular and variable. Given that, the current measurement are amazingly accurate. So I can identify about three approaches to doing this measurement, ...


3

These measurements were made by Michelson & Pease (1921) using the 100-inch Cassegrain telescope at the Mount Wilson Observatory. Modern-day interferometry typically uses multiple telescopes (e.g. IOTA and the Keck Observatory interferometer), as this is typically needed to achieve long baselines (with long baselines admittedly being less important for ...


4

This expression is valid for low frequencies, including the case of the 1420 MHz hydrogen line. It arises from treating the source as a black body with temperature $T(\theta,\phi)$$^{\dagger}$, and assuming $h\nu\ll k_BT$: $$I_{\nu}=B_{\nu}=\frac{2h\nu^3}{c^2}\frac{1}{e^{h\nu/k_BT}-1}\approx\frac{2h\nu^3}{c^2}\frac{1}{h\nu/k_BT}=\frac{2k_BT\nu^2}{c^2}$$ ...


1

I asked the at the minor planet center how the codes were decided, and the answer was Historically, the observatory codes were assigned ascending by longitude toward east (from prime meridian): 360 degrees were divided by numbers. When three digit numerical codes were not sufficient, letters plus two numbers were used again in bands toward the east. Some ...


1

SWAN seems to be on a parabolic orbit. This means that it is the first time that it is interacting with the Sun, making it a "new" comet. New comets are covered in a layer of very volatile elements that will vaporize pretty fast when the comet is still far away from the Sun. This causes a surge in brightness. But once those very volatile elements are gone, ...


2

There have been direct measurements, but they are quite delicate -- this is all the interferometry and so on. The simplest way though is based on spectroscopy, brightness and parallax. The argument goes a follows: The spectrum (how much light of each colour it gives off) is not hard to observe -- you basically just need a prism. The spectrum of most stars ...


5

NICER observations of PSR J0030+0451 in x-rays show hot spots clustered near one pole. The hot spots are presumed to be the termination of the active magnetic field lines, so there is really no magnetic "axis". The field is more complicated. First surface map of a pulsar


3

The other answers cover the geometric part, but that only tells you what fraction of pulsars are seen as such from Earth. The other issue is what fraction of neutron stars are pulsars at all. If they don't pulse, and they don't do something else conspicuous like accrete from a binary companion, neutron stars are very difficult to find. A common rough ...


13

It is believed that old pulsars may have their rotational axes closely aligned with their magnetic field. This would happen over a timescale of $\tau\sim10^7$ years (Lyne & Manchester (1988)). There are three sets of phenomena driving the dynamics of the alignment (Casini & Montemayor (1998)): Short-term ($\sim50$ days) variations caused by glitches ...


2

You can get into observational astronomy from a range of backgrounds. Some easily, some less so. Physics and data science sounds like a very fine choice as that is what can be a large part of an observational astronomer. You probably will have to learn a bit about image processing. And possibly about the physics of the objects you are going to observe. Such ...


17

The probability of seeing pulsed emission from a neutron star is simply the fraction of the sky covered by the beam, i.e. the beam solid angle divided by $4\pi$ steradians. The angle swept out on the sky by a pulsar with an emission cone of width $\rho$ turns out to be $$\zeta=4\pi\sin^2\left(\frac{\rho}{2}\right)$$ covering a fraction of the sky $$f=\frac{...


18

Out of 100 pulsars, how many will have a beam that crosses the Earth? About twelve. "The beaming fraction f , that is the mean value of the fraction of observable pulsars or the mean probability of observing a normal pulsar, is 0.124 ± 0.004." M. Kolonko et al.: On the pulse-width statistics in radio pulsars


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