# Tag Info

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,...

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. ...

14

It looks like the Mariner 9 era. Based on a review paper by Watters et al. ("Hemispheres Apart: The Crustal Dichotomy on Mars"): "The north-south asymmetry ... was clear from the first global image mosaics of Mars returned in the 1970s by Mariner 9 (Mutch et al., 1976) and the Viking Orbiters." Other papers cite a 1973 paper by Hartmann ...

13

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 ...

9

"Peculiar velocity" is a fixed term and describes the velocity of an object relative to a defined rest frame. Astronomy has the problem that you need different methods to measure the 3D motion of an object. Therefor one often only gives the velocity within line-of-sight (from spectrographic data) or the perpendicular velocity as measured from ...

9

All the binary mergers chirp, but the overall timescale of the event depends on the total system mass (or rather the chirp mass - see below). The more massive the system, the more rapid the evolution of the amplitude and frequency and the lower the orbital frequency when it finally merges. What you observe is also governed by the response of the detector - ...

9

In "The Planet of Doubt", Stanley G. Weinbaum, Astounding Stories, October 1935, there is a scene where Hamilton Hammond, leader of a expedition to the north pole of Uranus, explains his descision to set a southeastern course while searching for land: "I'll tell you. Did you ever look at a globe of the Earth, Pat? Then maybe you've noticed ...

8

From the first article you linked: Taking the first 3,200-megapixel images of a variety of objects, including a head of Romanesco – a type of broccoli – that was chosen for its very detailed surface structure, was one of these tests. To do so without a fully assembled camera, the SLAC team used a 150-micron pinhole to project images onto the focal plane. ...

8

I agree that it’s noise in a fixed pattern, but I think it’s unlikely to be related to ADC sensitivity. Typically if you have multiple ADCs, they read out blocks of the sensor (e.g. one on each corner to read out a quadrant). And sensitivity differences across those amplifiers usually is removed pretty well by flat-fielding. In my experience, you get things ...

6

That looks like a fixed-pattern noise to me. Fixed pattern noise is a common sensor artefact for CCD sensors, One source for this is where you have less analog - digital converters (ADC) than pixels. Say, you have N ADC, each with its own sensitivity. Then you have in the resulting image a sensitivity pattern which repeats every N pixels. Depending on ...

6

My opinion (and I think there has to be a large element of that) is that the presence, and ultimately identification of the orbital period, of exomoons is going to come from very precise transit photometry. If a sufficiently large moon orbits a planet, then this will leave its signature in the transit light curve. A "Fourier-type analysis" of the ...

5

What are these? These are used to reduce the aperture of the instrument. While you see three in this image, likely only one is removable. The instrument appears to be a Newtonian reflector. Which means it would have a secondary mirror near the front (and center). So the thing that looks like a knob in the center of the telescope cover is probably just for ...

5

Two things would be required. First, your line of sight would have to be close to looking along the magnetic axis of the neutron star. Second, that magnetic axis would have to be closely aligned with the rotation axis of the pulsar. If both of these are pseudo-randomly distributed and the pulsar beam is narrow, then this is inherently a very unlikely ...

5

Her Wikipedia page also includes this picture (public domain), where she wears the same dress, and where a similar display can be seen in the background: Roman sits at the control console for the Orbiting Astronomical Observtory satellite, launched in 1972 and nicknamed Copernicus. This is a publicity picture; she never actually worked in the Goddard ...

5

A small portion of Eugene Shoemaker's ashes were placed on the Lunar Prospector mission. After completion of the mission's primary objectives: Lunar Prospector was deliberately impacted onto the shadowed Shoemaker crater on the lunar surface at 09:52:02 UT July 31, 1999. NASA Mission Description No coordinates are given in that source, however, the Google ...

4

The part of the universe that we can see is a cone in spacetime (our past light cone) and there are young and old parts of the universe both inside and outside the cone. Here's a picture from Ned Wright's cosmology tutorial that shows what's going on. We're at the top center. The red lines are (a slice through) our past light cone. Ignore the wavy $\phi(x)$ ...

4

Discovery of Titan, 1655: Unknown diameter. Dollfus, 1970: 4,850$\pm$300km (1). Measured by Filar micrometer (2) and diskmeter / double-image micrometer (3). (Apparently a summary of earlier measurements, currently trying to find print copy) NASA SP-340, 1974: Summary of above techniques, propose settling on 5,000km diameter until it can be measured by ...

3

The really short answer is ... you don't (use Alt/Az data). You own a German Equatorial Mount that uses RA/Dec values and have no need of the Alt/Az coordinate system. A slightly expanded answer is that use of coordinates is meant to help you find objects. Realistically it would be challenging to do with your telescope mount because the RA/Dec setting ...

3

The brightness of light received from a light source (or an object that reflects light) is inversely proportional to the square of the distance. So if an astronomical object A which reflects light from the Sun back to Earth orbits at a distance of two AU from the Sun and an idental astronomic object B orbits at twice that distance, or at 4 AU, how much light ...

3

How the Vera C. Rubin telescope will physically carry out the actual survey of the sky (the Legacy Survey of Space and Time; LSST) is still subject to evolution and refinement. The broad survey strategy is set out in the LSST System Science Requirements Document which is (intentionally) relaxed on how it is actually carried out. The main requirements are: ...

2

I’d have to dig more to find some references, but the existence of $M > 30\ M_{\rm Sun}$ black holes was a big surprise. So a bunch of the events that have been detected are from a class of objects that wasn’t predicted at all. Originally I believe that neutron star - neutron star mergers were expected to be the main class of events. I don’t know how ...

2

When were these definitions formulated? Multiple religions have rather strict requirements based on sunrise / sunset, for example, when one must start or can stop fasting, or when exactly to sacrifice a lamb (or a human in some religions). The definition has very deep roots. Is this done purely because sunrise and sunset are the main examples of such ...

2

For a single dish radio telescope we define the primary beam as the telescope's response on the sky as a function of angle. What this means is that half way between the centre and edge of the primary beam, a radio source with a flux of 1 Jy will be observed to have a flux of 0.5 Jy. This response is circular i.e. it is a function of angular separation, and ...

2

This is not exclusive to spectroscopy applied to astronomy but general. Matter can interact with electromagnetic waves spanning a very wide range of frequency (energy). Also matter can emit electromagnetic radiation when in a kind of excited state. Due to the internal mechanism of absorption/emission it happens that the spectral characteristics can be ...

2

An alternative prospect might be direct imaging, although the systems that can detect raise the question of whether or not they count as planets/exomoons. As a possible example, see Lazzoni et al. (2020) "The search for disks or planetary objects around directly imaged companions: A candidate around DH Tau B." DH Tauri B is estimated as having 8–22 ...

2

The quote appears to be from the Ivezić et al. 2019 paper about LSST. In this context, σ quantifies the noise level in the images, and r is a photometric passband of ~620±70 nm wavelength. In single r-band images, they expect stars of AB magnitude 24.5 to stand out 5σ above the background level. δ refers to declination; they plan to cover the sky from the ...

1

I would've posted this as a comment, but I lack sufficient reputation. I like your idea of fitting three Gaussians, but I think you should try fitting with one large positive Gaussian and two small negative Gaussians. My physical justification for this is that I would expect a lot of self-absorption from the H-alpha line, which should be well-modeled using ...

1

While the image cannot tell whether one, two or three of the caps are removable two or three things can be said of what would be sensible: The central one likely is not removable as it is where the obstruction for the central secondary mirror sits. The other two - hopefully - are removable. Ideally those would be three openings forming a equally-sided ...

1

The coordinates of the object are not needed in order to track with a German equatorial mount. All objects move at a rate of 1 revolution in 24 hours (approx). You just point the scope at the object and turn on the drive.

1

The light that we receive from space contains a lot of information. Specifically, because of quantum nature of molecules and atoms, theses small species absorb light at very specific wavelengths.Each molecule, atom or ion has a unique set of absorption features. Think of it as the molecule own fingerprint. Hence, if we look at a star or a hot gas, we can ...

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