Questions tagged [observational-astronomy]

Questions about the techniques and practice of observing the night sky.

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2
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1answer
46 views

How much does the stellar radius change if seen through different filters?

I know that the radius of a star should be different depending on the filter being used to do the observation. That is, the bluer the filter, the smaller the measured stellar radius. I know this ...
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2answers
628 views

How exactly will DESI simultaneously capture individual spectra from 5,000 galaxies using optical fibers?

The BBC News article Telescope tracks 35 million galaxies in Dark Energy hunt says: The aim of the five-year programme is to shed light on Dark Energy - the mysterious force thought to drive an ...
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What is an “Off Rowland-circle Telescope”?

The NASA Goddard news item NASA to Demonstrate New Star-Watching Technology with Thousands of Tiny Shutters says: The technology, called the Next-Generation Microshutter Array (NGMSA), will fly for ...
2
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1answer
57 views

How will microshutter arrays be used in the James Webb and future space telescopes?

Question: How will microshutter arrays be used in the James Webb and future space telescopes? Are they acting as a sort of moving pinhole or slit, or is the pattern more complicated, like a coded ...
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35 views

IRAF: Identify task

I am trying to perform wavelength calibration on an image but I am stuck by the identify task under the longslit package. So when I type :go on the command line after I set the parameters (see the ...
3
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2answers
110 views

Venus-Saturn conjunction in Sagittarius on Dec 11, 2019 - How often does this happen?

Venus and Saturn will be approximately two finger widths apart in the constellation Sagittarius on December 11, 2019. I was wondering: how often do Venus and Saturn come together in the sky like this? ...
4
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1answer
102 views

What is a black hole's “shadow” and the best angle to view it to measure the spin?

This excellent answer mentions several ways to try to observationally measure the spin of a rotating black hole. The third one is intriguing, but I don't understand how this works: The spin of a ...
2
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0answers
35 views

Any night sky image databases

I was wondering if there were any available databases for photos of the night sky. It doesn't have to feature pictures of any particular star, just has to be a large collection of photos from the ...
2
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1answer
34 views

What equipment do I need to measure the spectrum of a star?

For an amateur astronomer, is it possible to measure the spectrum of a star? I can easily take a photo of a star just by putting a camera on one end of a telescope and over exposing it. But I would ...
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52 views

Can the patterns in the CMB be detected by off-the-shelf antennas/sensors?

I recently wrote a paper (will attach soon if feasible) for an astronomy class that analyzed the usefulness of the Cosmic Microwave Background as a static reference for attitude determination. The ...
2
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1answer
102 views

More recent data and simulations of “Milkomeda”, the collision of the Milky Way and Andromeda galaxies?

The Space.com headline Hubble Telescope Spots Two Galaxies in a Doomed (but Dazzling) Dance; The galaxies will ultimately crash into each other was probably overstated as seems to be policy in some ...
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97 views

What is the meaning of ellipticity of a galaxy being more than 1?

I was recently doing a project on calculating ellipticities of galaxies using SDSS data. I downloaded the stokes parameter values (q and u) from data $e = 1 - \frac{b}{a} = 1 - \frac{1 - \sqrt{Q^2 + ...
2
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1answer
74 views

How did they estimate the mass of Sgr A*'s companion G2 without knowing what it was?

Gizmodo.com's Astronomers Spot Unprecedented Flashes From Our Galaxy's Black Hole mentions Sgr A*'s companion gas cloud G2. That Wikipedia article says: First noticed as something unusual in ...
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1answer
53 views

Are red dwarfs (M dwarfs) known to be strong infrared sources?

If so, why? Are they known to be surrounded by large amounts of dust? Do they typically flare?
3
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1answer
66 views

SDSS Image Download: Swarp returns all zeros

In the CASJOBS Server, I created the following query for galaxies(DR12) ...
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1answer
64 views

What is the significance of minus sign in the expression of apparent magnitude?

The apparent magnitude of a distant object in the sky is measured as m=(-)2.5 log (I/I0) Where I is the intensity of the object whose apparent magnitude is to be measured and I0 is the reference ...
2
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1answer
42 views

Can we observe changes in the CMB (surface of last scattering) over time? [duplicate]

It is hard to determine the age of the Sun, because it won't change much over 100 million years or so. But what about the cosmic microwave background radiation, that is being mapped with ever better ...
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55 views

How far have stars been seen beyond the center of the Milky Way?

What lies near the center of the galaxy is of great interest and in recent times the motion of dozen(s) of stars at the center of our galaxy orbiting around Sgr A* have been measured in great detail. ...
4
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1answer
61 views

Expected nature of LISA's data; will it be more like a forest of static peaks, or a series of individual events?

@RobJeffries' clear answer to Which things “LIGO can see things that LISA can't”, and vice-versa? explains that the Laser Interferometer Space Antenna or LISA will only be sensitive to gravitational ...
3
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1answer
95 views

Tycho Brahe's model

Tycho Brahe made a model of universe where earth is at the centre and motionless whereas all other planet orbited around the sun. I am interested to know how he came to this model? If it is because ...
2
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1answer
68 views

Which things can LIGO see that LISA can't, and vice-versa?

CNET's Astronomers discover two ferociously fast stars locked in a death spiral quotes Kevin Burdge, lead author on the new paper in Nature General relativistic orbital decay in a seven-minute-...
2
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1answer
116 views

Is there a standardized “Astronomical Alert” system?

“Who saw” the binary neutron star merger first? What was the sequence of events? (GRB/GW170817) highlights a particularly notable astronomical alert, but I am sure that there are alerts triggered by ...
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1answer
957 views

Will LSST make a significant increase in the rate of astronomical event alerts?

The NPR news article and podcast New Telescope Promises To Revolutionize Astronomy updates the status of the "Large Synoptic Survey Telescope under construction on Cerro Pachón in Chile". NPR's Joe ...
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3answers
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Nicolas Copernicus discovery

As I was reading about the heliocentric model, a question came up: How was Nicolaus Copernicus able to figure out that the sun is at the center of the solar system, and that all planets orbit around ...
2
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0answers
28 views

Fermi-LAT gamma ray spectrum too high [closed]

I am extracting gamma ray spectrum from Fermi-LAT data. My spectrum is a lot higher than the ones on previous studies of the same object. What could cause a spectrum to go too high?
4
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2answers
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Any studies of the detection of dark matter in or near the solar system?

Has there been any theoretical or observational study of the possibility of detecting "local dark matter", either within the solar system or near the Sun in interstellar space? If so, what methods ...
2
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2answers
136 views

What would be the scientific impact of locating the Thirty Meter Telescope at its alternate site?

The NPR.org article Hawaii Protesters Block Access Road To Stop Construction Of Massive Telescope briefly summarizes the situation, one paragraph says: The TMT, as it is called, has been the object ...
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1answer
61 views

How can we estimate if a certain astronomical object will be visible from a place on earth?

If we have the RA/DEC of an object that we want to observe, how can we tell if that object is visible from our place on earth (at a particular time of the year)? Given that the part of the sky we are ...
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How to convert magnitude to spectral luminosity? [duplicate]

In the Gaia catalogue I have the magnitude of several stars in the G band. I also have the distances to these stars (parallax is known). Additionally, I oftentimes have the effective temperature in ...
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4answers
3k views

Are there any double stars that I can actually see orbit each other?

If I had a nice amateur telescope†, are there any multiple star systems that I could observe over a few years or a few decades and actually see the movement of one or both of them over time? My short ...
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35 views

What exactly is a Right Ascension clock and how was one (mounted on a telescope) used in practice, historically?

@MikeG's answer to Why does this Lowell Observatory telescope have so many knobs? What do they all do? explains that item #6 labeled in the image there (and cropped version here) is likely to be a "...
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34 views

Requirements for an amplifier and filter for a horn antenna-based 21 cm radio telescope?

We are looking into the possibility of building a low budget horn antenna for detecting 21 cm hydrogen line radiation (~1420 MHz) and and possibly measuring its spectrum. What are the types of ...
4
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1answer
85 views

How feasible is it that we could see the Central Black Hole Sgr A* occlude one of it's closely orbiting stars?

I'm thinking about the recent famous photo of a black hole, some months ago. It got me wondering if there isn't a way to more easily make a direct observation of these. We detect exoplanets in part ...
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1answer
56 views

How are “parallel fields” implemented on the Hubble Space Telescope?

The Phys.org news item Hubble is the ultimate multitasker: Discovering asteroids while it's doing other observations mentions the Hubble Space Telescope's use of parallel fields: A couple years ago,...
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6answers
2k views

How “fast” do astronomical events occur?

I've seen quite a few news about astronomy but I'm not deep into knowing how it works or how people observe it. It got me thinking: if I want to watch a supernova for example, how long will I have to ...
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1answer
56 views

Exposure time for spectroscopy compared to photometry

For a report I'm writing, I'm interested in comparing the exposure time required for spectroscopy versus photometry for a given magnitude. I found the figures on pages 7 and 8 of this lecture ...
4
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2answers
82 views

Draw the celestial sphere for latitude, showing the star Sirius, Estimate the approximate date when Sirius rises with the Sun

I'm having trouble understanding how to solve a certain problem. The problem is from the book Astronomy: Principles and Practice by Roy and Clarke. It is actually a solved example, but I am unable to ...
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0answers
33 views

Are occultation observations used/useful for orbit determination?

The IAU Minor Planet Center lists $(486958)\space 2014 \space MU_{69}$ "Ultima Thule" as having an uncertainty parameter of 2, based on the observation arc of 851 days, from its discovery in 2014, to ...
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0answers
49 views

Short term changes in celestial coordinates of stars

The right ascension and declination of stars change on a day to day basis. Some of the changes are quite large. The right ascension of Polaris, for example, changes by more than a degree over the ...
3
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3answers
146 views

Origin of heavier elements on earth?

Earth is part of Solar system, which is said to have originated from condensation and mutual attraction in dense clouds of gasses and dust. If Sun is basically more than ninty percent hydrogen and ...
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0answers
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How was the astrometry of the famous 1919 solar eclipse confirmation of General Relativity calibrated and verified?

The new New York Times article The Eclipse That Made Einstein Famous describes several events and discussions on the hundred year anniversary of the the 1919 solar eclipse and verification of the ...
2
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1answer
100 views

Second Telescope: Maksutov Cassegrain vs Refractor

I bought my first telescope, a 3inch refractor a few weeks ago. It has been a wonderful experience seeing the Moon , Jupiter, Satrun magnified and Andromeda, M33, M81 and much more for the first time. ...
0
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1answer
72 views

How Did Early Astronomers Measure Distances?

Prior to the era of radar and other forms of radio/RF/EM ranging, what approaches, methods, and techniques did early astronomers (e.g., Kepler, Cassini, Copernicus) use to measure the distance(s) from ...
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1answer
114 views

How were the orbital sizes determined in ancient India? [closed]

Rg Veda of ancient India contains a code that gives all planetary orbital information visible in the night sky. It is worth knowing the origins of our solar system and its development through the ages....
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1answer
76 views

Does the Zwicky Transient Facility only run when triggered by a cell phone?

A really enjoyable interview with Mansi Kasliwal & Samaya Nissanke ("From discovery to making precision measurements") is available as a short audio podcast in the BBC News article Gravitational ...
4
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3answers
124 views

How to properly observe Solar Total Eclipse in 2019?

I live in South America and I'm willing to travel to Chile in July 2019 to observe (in a curious way, not professional) the Solar Total Eclipse. According to my research, one of the best cities to ...
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1answer
23 views

How to convert the observed magnitude of a Quasar to it's bolometric luminosity?

How can I convert the observed magnitude to Bolometric Luminosity? I know the relation for the star but should it be same for a Quasar? Basically I want to convert the X-axis of this plot to ...
46
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3answers
10k views

If Earth is tilted, why is Polaris always above the same spot?

Why is Polaris, the North Star, always above (or near) the North Pole? If Earth is tilted, Polaris' path should be in winter 23 degrees away from its path in summer, or not?
2
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1answer
73 views

Which techniques are used to convert radio signals received by antenna to images?

I realized that after answering the question How do astronomers convert radio signals received by their antenna to images? I had missed the point that the OP was only asking about software. I've ...
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1answer
60 views

Where do local users of ALMA live and work?

These days with high speed internet, observational astronomy can be done from remote locations. Still I believe from time to time an experimenter might travel to work on-site for particularly ...