# All Questions

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4 views

### Chromatic abberation in lens

Is there a way to prevent chromatic abberation without using achromatic lens in refracting telescopes or in any other instruments...?
1k views

### Astronomical telescope making

I am thinking about making a telescope. I have a 100cm focal length lens which I can use as objective lens in my telescope. So which is the best focal length I can use as eyepiece in my astronomical ...
938 views

### Starting a fire in a cold planet that was full of flammable gas

What would happen to a cold planet that has a large amount of flammable gas, like Neptune, if we throw some fire into it? Will it burn, or would the flame be extinguished due to the cold?
102 views

### Right Ascension for epoch 2000 - physical location?

I understand that Right Ascension is a longitude-like celestial coordinate that varies from 0-24hrs, taken from a reference point of the vernal equinox. More specifically, for star maps that are based ...
13k views

### when are you able to see Halley's comet, and for how long?

I've been hearing about Halley's comet for a while now, and I'm just curious as to when and where to see it, and for how long. :)
23 views

### Solar degrees vs Calendar days

What is the difference between solar degrees and Calendar days. Is there any formula to convert one to another. for example Starting from 1/1/2000 1/1/2000 + 300 calendar days=some date (easy) 1/...
34 views

### Do Electric Charges in the Van Allen Radiation belt move in Opposite Directions?

The Wikipedia Article on Van Allen Radiation Belt gives the following explanation: A Van Allen radiation belt is a zone of energetic charged particles, most of which originate from the solar wind, ...
1k views

### Time according to the gravity of Sagittarius A?

This may be a really dumb question (I'm more of a Biologist than an Astronomer) so I apologize in advance for my little knowledge pertaining to Astronomy, but, if I'm not mistaken, time is effected by ...
300 views

### Why does the Solar Wind consist of charged particles?

The Wikipedia article on Solar Wind gives the following explanation: The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma ...
5k views

### Does time slow down because the universe is expanding at an accelerating rate?

If the universe is expanding at an accelerating rate, such that the galaxies' moving away from each other is accelerated, then time should also slow down. And when universe will accelerate to the ...
12 views

### How are concepts of Quantum Field Theory being applied in Astrophysics?

I've recently taken up a project with my professor on quantizing Real, Complex, Dirac and Maxwell's Field using Dirac's method of constrained systems and Fadeev-Jackiw (FJ) and improved FJ ...
25 views

### Does plasma recombination in the solar wind happen to any significant or measurable degree?

Comments below this answer to Why does the Solar Wind consist of charged particles? have led me to ask the following: Question: Does plasma recombination in the solar wind happen to any significant ...
28 views

### Does Gravitational Time Dilation stack on top of Time Dilation caused by Velocity?

Using 1 CM from the Event Horizon of Super Massive Black Hole, SGR A, as the reference point. The particles within the accretion disk are traveling at extreme high speeds. Assume this speed increases ...
49 views

### Why do J2000 coordinates change with time in Stellarium?

I'm new to the field so I'm sure this is a basic misunderstanding. As I currently understand it, J2000 equatorial coordinates describe the position of objects by referencing a specific point in time (...
20 views

### Why is it hard to reconcile Gaia DR2 with the HIP data set

I'm trying to get a database of about 20 million of the brightest stars in the sky for a project I'm working on, and I want to reconcile it with the Hipparcos data set. Currently, I'm only using the ...
30 views

### Why do we expect Type Ia Supernovae to be brighter in a decelerating Universe than what has been observed?

This seminal review paper in the PNAS by Robert P. Kirshner (https://www.pnas.org/content/96/8/4224) says the following: If the universe had been decelerating—–in the way it would if it contained ...
331 views

### Characteristics of the first planets in the Universe?

What would have the very first planets looked like, based on their most likely chemical compositions? For example: Were they mostly grey gas giants with atmospheres of hydrogen and helium, ...
65 views

### How to calculate phase angle of a satellite?

I'm making a program for predicting satellite passes. I'm trying to find out if the satellite is illuminated by the Sun and not in Earth's shadow. I need to know its phase angle: the angle between the ...
59 views

### How spectrographs that measure radial velocities manage to translate variations in the stars' spectrum lines into the “speed” of the star?

Like ESPRESSO or CARMENES, for example. I just don't understand the process or the way these spectrographs manage to obtain the velocity of the "wobble" of the star (due to the presence of another ...
68 views

### Fastest recorded apparent motion of a comet or asteroid seen from Earth (degrees/day)?

If I've done my maths correctly in this answer comet 2I/Borisov (C/2019 Q4) was seen to move about 0.2 degrees in 7 hours, which is almost 0.7 degrees per day. I'm assuming this is pretty rapid ...
2k views

### Reason for disqualifying Pluto as a Planet? [duplicate]

Pluto is no longer a member of the planets in the solar system. Why was it disqualified as a planet? What is the criteria for classifying an Astronomical Object as a Planet? Does this criteria apply ...
3k views

### What mechanism causes oscillations of the solar system's orbit about the galactic plane?

In a recent paper (news release here) Lisa Randall and Matthew Reece propose that a dark matter disk coinciding with the galactic plane together with the solar system's oscillations through the ...
2k views

### Coordinate system for space

I am high school student, I have doubt if I have to locate a planet or any star in space, how do I locate it, because we have no perfect coordinate system, I have read in some books, that time is ...
3 views

### Curiosity landing system versus Spirit/Opportunity's [migrated]

Spirit/Opportunity used airbags to land while Curiosity had a "carrier" with thrusters and chords - which to me sounds heavier and much more complex, therefore also riskier. It seems that it would ...
121 views

### What do the fusing 'onion layers' of a pre-supernova star look like to scale?

I'm sure we've all seen the diagrams of various layers of element fusion from hydrogen to silicon in a star that's just about to go supernova. (Picture from courses.lumenlearning.com) I suspect ...
86 views

### Did Hubble see a pair of UFOs? (Identify this artifact)

The image below is this one, found in this group of Hubble space telescope images of the interstellar comet 2I/Borisov (C/2019 Q4). Can anyone recognize this pair of artifacts in the upper right ...
1k views

### Where to obtain Tycho Brahe's data?

I would like to obtain Tycho Brahe's data on Mars. What would be an authoritative source? One source I could find is this page (the data is given as an Excel file) but I have no idea can that be ...
34 views

### Questions about Hubble's brand new view of an interstellar comet (video)

This GIF is made (via giphy.com) from the new NASA Goddard video Hubble's New Image of Interstellar Object and if I understand correctly many (if not all) of these frames are from https://archive....
116 views

### Cosmological redshift vs doppler redshift

I'm reading Harrison's "Cosmology: Science of the universe" because Harrison focuses on the distinction between cosmological redshift (he calls it expansion redshift) and the Doppler redshift. He ...
25 views

### Photometric redshift - empirical methods (machine learning)

I am currently learning about estimation of photometric redshifts with machine learning methods (or empirical methods in general). These methods use the knowledge about the photometry and the ...
3k views

### Which are stars and which are noise in this comet photo?

The Forbes news article NASA's Hubble Telescope Snaps Best Images Yet Of Our First Interstellar Comet shows the image below (which I have since annotated) of comet 2I/Borisov (C/2019 Q4) and links to ...
103 views

### The dominance of Gravity vs Strength and its dependency on crater size

So I am trying to write a research paper (about 3700 words) for high school about the topic "The dominance of Gravity vs Strength and its dependency on crater size" or something similar. I have ...
14k views

### How loud would the Sun be?

Sound can't travel through outer space. But if it could, how loud would the Sun be? Would the sound be dangerous to life on Earth, or would we barely hear it from this distance?
5k views

### Can things move faster than light inside the event horizon of a black hole?

Black Holes are regions of space where things get weird [Citation Needed]. Past the event horizon of a black hole, any moving particle instantaneously experiences a gravitational acceleration towards ...
59 views

How to plot Doppler profile corresponding to the spectral line? The spectral line was plotted from data: flux with respect to wavelenght and I know the temperature. These two function are Doppler ...
489 views

### How far away is the nearest compact star remnant likely to be?

Neutron stars and black holes are hard to detect when they are solitary, and there seems to be big uncertainties about how common they are. White dwarfs are much easier to detect and the nearest one ...
74 views

### Time dilation due to the expansion of the universe

This is not a homework question. I want some help in being able to clearly perceive the expansion of the universe and the consequences thereof. We know that the universe is expanding in an ...
66 views

### Why was Dawn's (the spacecraft) flight path circular? [on hold]

In comparison to the twin Voyagers, Dawn's flight path circled the sun in an anti-clockwise manner. The map of its path shows its targets, Ceres and Vesta were in a trajectory that was close to a ...
67 views

### Calculating historical star maps from proper motion

I'm working on some software which needs to calculate the position of stars and galaxies visible to the naked eye at different periods of human history. The Yale Bright Star Catalogue gives the ...
75 views

### Is intrastellar commonly used by astronomers to refer to objects within our solar system?

The CNET article Interstellar comet Borisov looks ordinary, making Oumuamua even weirder says: A paper published Monday in Nature Astronomy lays out the early data on Borisov, which is just the ...
40 views

### Overhead (galactic North) view of the stars in and around the Vela Constellation with distance

I am working on a project and would like to have a star map--seen from "above" (Galactic North?) that calls out the stars in the Vela constellation and shows their distance from sol / earth. I ...
75 views

### How would a planet's gravity affect an object longer and wider than its equator? [closed]

Imagine a flat object slightly wider than a planet's surface area whose mass is much lower than that of said planet. If it landed on this planet, would the curvature of gravity bend it, or possibly ...
1k views

### Why can we observe the Cosmic Microwave Background no matter the direction we look?

I often read that the CMB was released from everywhere in the Universe, in every direction. If that statement is true, can someone elaborate what "everywhere in the universe, in every direction" ...
61 views

### Seeing a star near zenith around sunset

I'm recalling while taking a university astronomy class the professor brought a few of us up to the observatory, around sunset. He showed us a star near zenith with the telescope. After we left the ...
41 views

### How to calculate the orbital velocity, the high-orbit (quasigeostationary) holding force and the shadow of the disk on Earth? [closed]

[] The following data are given: • The circular orbit of the disk D (quasigeostationary orbit) parallel to the geostationary orbit. • Located 4,505 km to the north of the equatorial plane, above ...
24 views

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 ...
68 views

### Is there a way to tell the difference between earth andesite from Mars

I'm curios if there is a way to test if this sample might be Martian andesite. What type of oxygen isotope (or other) test can be done to address this in some way? As background, any information ...
536 views

### Why do shooting stars burn close to the ground sometimes?

I saw a shooting star as I was standing on the roof of my home. My home is double storey. And the height of that shooting star that I saw was maybe 10 to 13 meters. It was burned down at that height. ...
There is formula for stars sideral time: $$ra - \arccos(-\tan(dec)*\tan(lat)).$$ where $ra$ - is right of ascension at the vernal equinox. $lat$ = latitude $dec$ = declination Is it applicable ...