# Tag Info

## Hot answers tagged observational-astronomy

46

It's not very surprising that no Oort Cloud objects have been detected via occultations. They're extremely rare, even for our most advanced space-based observatories. According to Ofek & Nakar 2010, published about one year after the launch of Kepler, the telescope would be able to detect between $0$ and $\sim100$ occultation events of Oort Cloud objects,...

45

correct for the distortion An imperfect mirror does not produce a distorted image - it produces a blurry image. With light-field sensors and phase imaging, one could possibly correct for the blur, but it is much more challenging problem than normal lens distortion correction. Distortion refers to a systematic change in how shapes are projected in an image. ...

38

(Much of this echoes what antlersoft says in their answer) For a phone photo through the eyepiece that looks about right to me! The size... the brightness... both are as I expect. What you could try is to use the manual mode of your phone's camera and set the ISO down to minimum (100) and the shutter speed down to something like 1/60s. Take a few shots, ...

35

This can get a bit confusing, because "arcminute" and "minute" are both sometimes used in celestial coordinate systems but mean two different things. An arcminute is 1/60th of a degree, and an arcsecond is 1/60th of an arcminute. That's simple enough, and when talking about small angular distances, it's often much handier to refer to ...

33

Jupiter can be seen during the day. This image is by Philip Crude. Philip is an experienced astro-photographer. On his webpage http://www.billionplanetsquest.com/p/planets.html he gives details of the equipment and settings used: This image was captured through my [i.e., Philip Crude's] Celestron CGEM-800 using a ZWO ASI120MC camera at prime focus. ...

32

How was the mass of Venus measured for the first time? In the mid 19th century, Urbain Le Verrier's predicted of the existence of a then unknown planet beyond the orbit of Uranus. He even predicted this planet's orbit. The discovery of Neptune based on his predictions was perhaps his greatest accomplishment. Le Verrier then went on to investigate Mercury. ...

31

Let's say we have a spherical shell of some material emitting light, much bigger than the star it surrounds. If we look right down the center of the shell, our line of sight takes us through only a small amount of gas - not enough for there to be significant emission. On the other hand, if we look at the nebula near the outer edge, our line of sight takes us ...

29

No, it cannot. Far from it. The closest approach between both planets is roughly 16 AU due to the 3:2 orbit resonance. Pluto will even then be a tiny dot among many with a brightness around 14 mag. You can try that with Stellarium yourself, placing the observer on Neptune and looking for Pluto. You just have to find the right time. One such time is approx. ...

28

Tl;dr, From personal experience, it’s not worth it. It’s a lot easier to throw away bad data than to try to calculate when stop. There’s not a lot of ambiguity as to whether it messes up the data. As of right now, it’s not that big a problem either. Sure, some are particularly unlucky, as seen with a Magellanic cloud observation in early 2020. The concern is ...

26

Also see answers to Could mirrors be replaced with CCDs? Is Digital Adaptive Optics Possible? The problem is that light imaging detectors convert amplitude to power during the detection process. Phase is lost. If you had maps of both the magnitude of the electric field and its relative phase, and had this at each wavelength of light, you could do exactly ...

26

Yes, but not in the exact way you think of. To avoid light pollution it is better to go sideways. If you are in a light-polluted city, there would still be light pollution at an altitude of 400ft (the maximum operating altitude of drones) And, moreover, amateur drones are not powerful enough to carry a telescope of any useful size. So you will find that ...

23

You correctly state that neutrinos do not interact too often. The physical parameter describing that is the effective cross-section. So what you observe in a detector is not the neutrino itself, but secondary particles, e.g. muons. Colloquially put, you may regard anything with high mass (density) in between the neutrino source and your instrument (to detect ...

20

It's very difficult to get any kind of picture just holding your phone up to the eyepiece, and the picture you posted is overexposed and probably motion-smeared, but other than that it's what you'd expect. Planetary observation is a learned skill; planetary detail is usually very low contrast. Mars is a small target and you have to use lots of magnification,...

20

Short Answer Thin gas in a nebula only absorbs some portion of star light corresponding to a small subset of the overall visible spectrum, according to the corresponding molecular composition of the nebula. For even these limited spectral ranges, the star is still often visible in a nebula since the gas can be too thin to absorb all the energy emitted by the ...

17

The mass of Venus was determined by weighing the Earth, or more precisely, by determining the ratio of the density of the Earth to the density of Schiehallion, and assuming Schiehallion to be typical rock of 2500 kg per cubic meter. Prior to that, Jérôme Lalande had worked out the relative masses of the major bodies of the Solar System as a byproduct of ...

16

Amateur equipment is good enough. But you cannot detect it with a naked eye. The change in flux for a passing exoplanet in transit is roughly 1%...2% at most for the larger exoplanets - and it is a gradual change. That's a change you do not notice with the naked eye, but it needs photographic equipment to create a sequence of images which allow analysis of ...

16

For the most part, the CMB photons travel directly to our telescopes from the surface of last scattering. Some corrections need to be made to determine the blackbody nature of the spectrum, but they are not corrections for absorption of the photons. The two main corrections are shown clearly by this COBE image sequence: (from here). First, the motion of us ...

15

Supplemental answer based on @JamesK's When looking at an object through Earth's atmosphere, we know that it removes some light multiplicatively due to absorption and scattering contributes some light additively due to things like scattered light from other sky objects (e.g Moon and now Sun) and skyglow. During the daytime you can dramatically improve your ...

15

The so-called 'mass gaps' for black holes, according to theoretical models, are between 2-5 solar masses and 50 to 150 solar masses. (Actually, I have read that there is no good theoretical reason for the lower, 2 to 5 solar-mass gap....) The lower mass-gap is suspected observationally because we have yet to observe a neutron star with mass greater than ...

15

The image which is recorded by CCDs are the convolution of the true image and a point spread function. If the PSF is not a nice function, such as this one, for example [source]: then (I think) it is hard to deconvolve the detected image from the PSF to get the true image. For example, you don't necesserily know the exact PSF if the telescope is only "...

15

Your trigonometry book isn't wrong: both "minute" and "arcminute" can refer to $\frac1{60}$ of a degree. It's certainly a very good idea to use the term "arcminute" when referring to $\frac1{60}$ of a degree, but it's not essential if there's no ambiguity, eg, in a static geometry problem where there's no mention of time. The ...

14

According to the NASA Pluto fact sheet, the brightest that Pluto gets is an apparent visual magnitude of 13.65 when it is 28.6 au from the Earth and (presumably) about 29.6 au from the Sun. To work out how bright that would be from Neptune we could work out how close Neptune can be to Pluto when Pluto is at perihelion. This is complicated by the fact that ...

14

On what basis is the information about the distance and velocity of the Voyager probes determined? For distance: round-trip travel time of radio signals For velocity: Doppler-shift of round-trip radio signals, and by the rate of increase in distance as discussed above. The Voyagers as well as many other deep-space spacecraft before and after carry what's ...

13

I would be extremely concerned about the ability of such a telescope to make adequately precise measurements, given the motion of the water. The leading radio telescopes have their mirrors and receivers very exactly aligned. For example, Arecibo's Gregorian dome could be aligned with any location on the order of millimeters, while the Green Bank Telescope's ...

13

I think your requirements can be met by Stellarium. It is a freely available open-source planetarium software available for PC, and can be used offline. There is also a web version, which you can try out here. You can filter stars out by pollution levels, as illustrated in the stellarium wiki. Here is an Astronomy Stackexchange answer on matching the ...

13

Yes, comets spin although measuring it can be tricky due to the coma and outgassing from the nucleus. It's easiest to measure the rotation period when the comet is inactive near aphelion although this is more difficult as the comet is fainter, necessitating a large amount of large (>4m) telescope time which is difficult to obtain. Searching the JPL Small ...

12

Moon as reference point With a bit of patience, you can wait until the Moon is: not too close to the Sun close to the planet you would like to watch If the angular separation between the Moon and the planet is less than ~5°, you can use Stellarium to know in which direction you should move your telescope. You can use the terminator as a reference line, ...

12

TLDR; Its a diagram showing all the physics and modeling choices that go into different models (the colored boxes in the middle) to compute an SED. Longer answer: First a SED is a spectral energy distribution, i.e how the amount of light varies as a function of wavelength. These kind of plots help understand to understand the underlying physics of an object. ...

11

Your best bet is probably a distance-limited catalog designed to include everything within a specific distance. The most recent such compilation I'm aware of is Reylé et al. (2021), which has a limit of 10 pc and includes slightly more than 300 (hydrogen-burning) stars, along with about 20 white dwarfs and several dozen brown dwarfs. They note that they are ...

11

It is not possible to know. The speed of light is the speed of information. The information "the star has exploded" cannot travel faster than the speed of light, so there is no way to know that a star has gone supernova before that information reaches us. Usually the first particles to reach us from a supernova are actually neutrinos, which can ...

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