# All Questions

3k views

### Is a white dwarf hotter than a Red Giant?

From what I've read, white stars are hotter than red ones. But a white dwarf would have just heavy elements to fuse, so shouldn't it be less bright?
42 views

### How to find maximum and minimum right acsension and declination based on the telescope's location?

If I am to apply at a telescope for viewing objects, how to determine (easily) what is the minimum and maximum possible RA and DEC visible from that telescope during that time of the year. For eg, ...
30 views

### Moving-Cluster method for determination of the distance of Hyades. A starter problem

I am currently following a class of observational astronomy lab. I will present a brief description of the method in first and then proceed to the question, so anyone is welcomed to read the entire ...
138 views

In the Big Bang model of the Universe, every observable thing is thought to have expanded very abruptly from a point of infinite density and zero volume. However, the problem with this assertion is ...
5k views

### Why did the moon abruptly change positions in the sky?

Three or four weeks ago I was outside showing my neighbors how cool the moon was through a 'backyard' telescope in broad daylight (~8PM PDT). It was 3/4 of the way across the sky (setting behind the ...
139 views

### Why does the Chandrasekhar limit affect white dwarfs differently?

The Chandrasekhar limit is the maximum mass of a stable white dwarf star. Beyond this, a carbon-oxygen white dwarf will typically explode in a type 1a supernova, due to the nuclear reactions at those ...
105 views

### Why was the size of the solar system not defined by Mercury Transits?

The first measurements of the (absolute) size of the solar system was made using the Transit of Venus, an event that arguably will only happen twice in a lifetime. Transits of Mercury occur far more ...
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We have discovered about 2500 radio pulsars. Part of them show pulsations in other bands like X-ray and gamma ray. The radiation mechanism remains unclear now. I wonder whether there are radio ...
102 views

### Distance of a planet to the star?

QUESTION: Suppose we discover a planet orbiting a nearby star. The distance to the star is 3 pc. We observe the angular radius of the planet’s orbit to be 0.1 arc sec. How many AU from the star is ...
31 views

### Topography / elevation data of Mars

For a design project I'm looking for elevation data for Mars' surface - the idea is to replicate a surface area of Mars as a physical model, using the elevation data to create a very rough 3d model of ...
72 views

### How can we explain high redshift numbers?

I just finished an introductory astrophysics course$^1$ and I have a lingering question that I can't seem to resolve. We learned that for the first few hundred million years, the universe was pretty ...
62 views

### uses of coordinate systems

Wikipedia describes the five following celestial coordinate systems each with rectangular/spherical variants: horizontal equatorial ecliptic galactic supergalactic What are the practical preferred ...
52 views

### Eclipse — Solar and Lunar

Q. Why is solar and lunar eclipse not seen from all parts of the earth at the same time? I think its because of the revolution of the earth but i am not sure. I want a more reliable answer.
55 views

### How many stars are there in a Globular Cluster of 10^5 solar masses?

I was wondering whether there is an easy way to approximate the number of stars in a Globular Cluster (GC) with 10^5 solar masses. Can one, for instance just assume the GC is made of sun-like stars ...
128 views

### Can life survive on the equator of cooled and fast rotating white dwarf or neutron star?

As I know, some stars produces carbon, nitrogen and oxygen when they are old and become white dwarfs or neutron stars. And even their surface gravity is strong, it may rotate very fast so that the ...
97 views

### Why (actually) aren't ground-based observatories using adaptive optics for visible wavelengths?

Adaptive Optics (AO) techniques allow ground based observatories to dramatically improve resolution by actively compensating for the effects of Astronomical Seeing. The atmospheric effects are quite ...
2k views

### What's the likelihood of the existence of unknown elements in the Solar System?

What's the chance that there might be undiscovered chemical elements in the Solar System - either on planets or around the Sun or on asteroids of the Oort-cloud?
34 views

### How to calculate the pixel size and beam size of an image?

I have an image with some sources in it. I need to get the pixel size and beam size of that image. How can I calculate it?
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### What would the night sky look like if the interstellar medium didn't exist to absorb or block light?

I was curious about how much brighter it would be and how much further we could see.
39 views

### LLR & Orbital Motion

As I understand it, light that is emitted from a source is not imparted with the motion of the source and so always follows a "straight line". If this is correct, I am having a difficult time ...
87 views

### Finding a location using the direction of shadow, UT and date approximately

Does anyone know how to find a location by using : the direction of shadow relative to the normal (for example azimuth angle) the Universal time (UT) and date I have a satellite image and I know ...
50 views

### Solar / lunar positions in ECEF using SOFA C libraries

I'd like to calculate the positions of the sun and moon in the ECEF coordinate system using the SOFA (http://www.iausofa.org/current_C.html) libraries given a Julian day input. So far, I've got this ...
43 views

### Metalicity and age of bulge stars vs halo [duplicate]

From what I understand of current models, the bulge of the galaxy formed first, and thus, would contain older population II like stars. Currently, however, the halo has a higher population of stars ...
51 views

### Would a telescope that uses Fresnel lenses be more practical than using regular lenses?

If we were to make telescopes with Fresnel lenses instead of regular lenses, would it be more practical? Would this also allow for much bigger telescopes to be made? Here is an example of the type ...
38 views

### Why weren't the Hubble light-echo images of V838 Monocerotis supplemented by ground telescopes?

Drawing from this answer The V838 Monocerotis expansion (not a supernova) and the observation of the subsequent "spectacular" light echo was quite a notable event! From Nature 422, 405-408 (27 ...
49 views

### General question on Solar Eclipse

Let's assume 'solar eclipse' occurred Now, at what degree 'moon' will be in 'with reference to' earth (and) at what degree 'moon' will be in 'with reference to' sun In other words, by 'how many ...
40 views

### Intuitive explanation for why the universe is flat

I went through Prof. Hitoshi Murayama's online lecture where he describes why the universe is flat. One of the evidences for a flat universe is the evenness of CMB radiation on all directions. My ...
52 views

### What visible star is closest to the ecliptic?

If we were to project the ecliptic out as an infinite plane, what visible star (besides the sun) would lie closest to it?
334 views

### How to calculate the temperature of a star

I need a way to calculate the effective temperature (surface temperature) of a star for a stellar model. I need something in the form Te=.... I have: Radius in m mass in kg the composition of ...
83 views

### Term for altitude of the sun?

The sun travels in an arc across the sky. Where I live, during the summer the arc rises higher, but in the winter the arc is lower. Once might speak of highest altitude or elevation the sun reaches ...
299 views

### How are rogue planets discovered?

Planets are usually found by observing a star and waiting for the light level to drop when a planet passes in front of it, but what about rogue planets that don't have host stars?
125 views

### Are we made of stars we're seeing? [duplicate]

a fresh astronomy enthusiast here. Recently I've been reading upon how immensely far other stars are from our solar system and how is it possible that we may be seeing stars that are already dead. My ...
40 views

### Calculating Orbital Period

I was using this formula to calculate the orbital period of a satellite in days: T = sqrt[(4*pi^2)*R^3/GM-center] Where R^3 is the radius of the orbit, or distance of the semi-major axis, G is ...
157 views

### Chemical reactions in white dwarf and carbon allotropes

White dwarfs consists mostly of carbon and oxygen. In my opinion, they are too hot to contain these elements in molecular form and hence chemical reactions does not happen (I think resulting CO2 will ...
154 views

### Could we verify the structure of a black hole by observing an orbiting object?

Can we determine the physical structure of a black hole by observing its gravitational effect on objects in orbit? There are three possibilities that I see, and would like to test: Singularity at ...
138 views

### Is it possible for the Sun and the Moon to crash into each other? [closed]

Is it possible for the Sun and the Moon to crash into each other? If yes, under what conditions? If no, why?
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### Can dark matter be explained by a nearby universe? [duplicate]

There is a conjecture in string theory wich says that dark matter is the result of a nearby universe. Suppose we live, to make things imaginable, in a line on a very small cylinder, then on the other ...
12 views

### Calculating orbits for beginners [migrated]

I'm a game developer, and I'm working a space game, where I have to simulate a spacecraft's orbit, traveling from the earth to the moon. I would need the apoasis and periapsis of the orbit. I have the ...
45 views

### K-Pg asteroid impact

Is it possible to determine what daytime the Chicxulub impactor striked the Earth 66 mya? Was it day or night, what was the current phase of the Moon etc.? Can sediments, rhytmites or something else ...
86 views

### Solar Elevation Angles — Anomaly?

"The solar elevation angle is the altitude of the sun, the angle between the horizon and the centre of the sun's disc." - Wikipedia The meridian is when the sun is directly facing earth and is at ...
88 views

### Was NASA's moon mission completely fake? [closed]

I really want to know whether NASA's Moon mission really was a hoax, or if it is a fact. Since there are many points and scenarios which proves it as being filmed in a film studio with controlled ...
55 views

### V838 Monocerotis “light-echo” images morphed into nice video, but why so few original images?

This NYTimes video shows what I think is a series of real Hubble images which have been "morphed" artistically to appear to be continuously expanding. (also see The V838 Monocerotis Star Still Has ...
47 views

### Does a self-gravitating gas necessarily develop turbulence?

Though we may still doubt the exact driving mechanism of turbulence in each particular case (ISM, MC, circum-BH/-stellar discs, atmospheres...), can I say that in a sphere of dark matter particles no ...
80 views

### When was the nearest star discovered? [closed]

When historically did we realize that the Sun is a star, like all the others? An answer was posted, then the question was put on hold. I would like to answer: If indeed someone asserted that the Sun ...
46 views

### Why Free-Free emission is regarded as Thermal emission?

I read that thermal emission/radiation are the ones whose spectra is similar to that of a Black body radiation. Also thermal radiation depends solely on the temperature of the object. How can we ...
14 views

### conditions of the early universe and inflation [duplicate]

According to our current understandings (The Inflation Theory) when the universe initially expanded it pushed space and time outward from a point. So if anything was present in the space at that ...
65 views

### How to interpret extreme ultraviolet/ x-ray data in the literature?

I am interested in a sun-like star 138 light years away that is in the EUVE catalog. A table shows that a photon count of 2.6+/-0.5 photons per kilosecond at 100 angstroms has been detected for this ...
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### Why do post main sequence stars enter the red giants branch?

I am an early graduate student in astronomy and have hard time understanding why do post-MS stars move up the RGB. Here is what I understand about post main sequence evolution of stars. As their ...