# All Questions

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### Calculate time when star is above altitude 30°

To find the best observation time for an object, I'd like to calculate the time when it is 30° or more above the horizon. Local Sideral Time would be sufficient. To include that in my program, I need ...
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### Oscillation in tilt of the solar system

I know that the solar system is tilted 62.6° to the plane of the galaxy. I'm curious whether this angle changes over time, and what are the extents and time frame of any such oscillations if they ...
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### Are there currently observed systems of close (narrow) binary brown dwarfs?

All over the Universe, there are (gravitationally bound) binary star systems. Considering the huge number of brown dwarfs, are there currently known double systems of gravitationally bound binary ...
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### Definition of stellar core?

This is a basic question, but I may as well ask it. I had always thought that the core of a main-sequence star is defined as the part hot enough for nuclear fusion. Some dictionaries seem to agree ...
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### What kinds of stars would it be possible to observe in M31 with a small amateur telescope?

I was wondering what kinds of stars would be visible in M31 and other nearby galaxies using a moderate (~8") telescope and a CCD camera. This would be a limiting magnitude of around 17. I have heard ...
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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 ...
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### Is the Sun slightly blue in the center? - Wavelength-dependent limb darkening of the Sun

I've slightly modified the title to try to attract some attention. If we call sunlight "white" and limb darkening is a result of seeing deeper at normal incidence and shallower at oblique incidence, ...
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### What is the magnitude of variation of Earth's orbital inclination?

Please excuse if this has been asked and I just didn't find it. I have found several references that indicate that the inclination of Earth's orbit varies over a period of ~70,000 years, but I can't ...
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### Would the (orbitting) speed of the earth change if suddenly the sun disappear and the earth is thrown into space?

Usually an orbit is considered as an acceleration. So fe the earth has a speed of about 100.000km/h around the sun. Now I think there is some relativity involved, so from which point of view shall we ...
114 views

### Can a star eject a liquid or a gas that has not been ionized?

Can a star eject a liquid or a gas that has not been ionized? I am implying that these gases could be a source of reusable energy.
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### What is 'Dark Fluid'?

Is this term official jargon/wording for 'Dark Matter'? If so, why include the word "Fluid" if there is supposedly no viscosity in actual space. It would be like saying 'Hey, want to go swim in my '...
160 views

### What's the distinction between “planetary formation mechanisms” and “gravitational collapse”?

As I was curious about the exact identical comment to my title here: http://astronomy.stackexchange.com/a/16135/10102 And as it seems no one asked it yet, I'm simply interested in the difference of ...
110 views

### Could asteroid mining affect gravitational balance?

I'm just a guy who is interested in all topics around space, so forgive me if it is a dumb question. I have read some things about asteroid mining in the past and I think it's a really interesting ...
188 views

### How did the Earth come to be in orbit around the sun?

I'm not sure if this post should be in the physics subject forum, but this seems to fit here too. I have been reading a book about chemistry and how the universe came to be with the theory of stars ...
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### Does the summit of a small mountain offer better seeing?

I have a small amateur telescope, and would like to defeat the atmospheric seeing conditions as much as is possible. Fortuitously, I happen to live fairly close to this lovely patch of bare elevated ...
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### Pointing direction movement of a fixed camera

first doubt here: I have a fixed camera, whose coordinates I know, pointing to the sky. After the first image, I performed a astrometry calculation from nova.astrometry.net and I got, among other ...
194 views

### How cold is interstellar space?

The vastness of space brings me a sense of chilliness even though I have never experienced it, although I wish to. Just how cold is interstellar space (on average)? How is this even measured? I mean ...
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### Theoretically could the expansion of the universe affect acceleration due to gravity?

I was wondering if theoretically the universe expanding affects speed or acceleration due to gravity, compared to if space weren't accelerating. The way I have it in my head, something is falling ...
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### 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 ...
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### 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.
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### What other “planetary formation mechanisms” exist beyond “gravitational collapse”?

My curiosity was pricked by the an edit made to this post: What other "planetary formation mechanisms" exist beyond "gravitational collapse"? sadly the edit was changing the ...
42 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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### 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 ...
210 views

### Confirm: We can only notice planets if their orbit passes in front of their star and our view

If we can tell a planet exists by the dimming of the brightness of a star when it passes in front of our view of the star does that mean we cannot see a planet if it does not cross in front of our ...
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### 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 ...
66 views

### Was the radiant of the Perseid meteor shower ever near Vega thousands of years ago?

The ancient Chinese story of the Weaver Girl (Altair) and the Cowherd (Vega) tell of starcrossed lovers who are only allowed to meet once a year on the 7th day of the 7th (Chinese) lunar month, ...
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### Books describing first-hand experience of astrophysicists finding planets without skipping actual maths

Are there good references of astronomical texts where we get a first-hand experience of astronomers uncovering astronomical gems using maths alone and not using observation. Observation may have been ...
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### 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 ...
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### Is there a name for the maximum in local solar elevation angle?

It came up in conversation today that we were nearly at 21st June, and the days would shortly be getting, um, shorter. We were trying to think of the the term that means "When the sun is at the ...
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### How useful are filters for spotting nebulae?

Recently I've been trying to spot a couple of nebulae, IC59 and IC1318. The skies at the site are modestly dark (4.5 on the Bortle scale), I'm using an 8" scope, and I've slowly scanned around the ...
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### 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 ...
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### What are the possible solutions to the Red Supergiant problem?

I have recently come across this so called "Red Supergiant problem" in the literature, a phrase that was coined by Stephen Smartt in 2009 in reference to why red supergiants with masses ∼16-30M⊙ have ...
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### What exactly is this VLA radio image of Jupiter showing?

This VLA image is beautiful, and instructive, but I don't understand it fully. This version is from an article in Gizmodo where the credit reads: A radio image of Jupiter captured by the Very ...
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### Question related to Sun rise and Sun set times

I am not sure whether this question is right or not so bear with me. I understand 'Sun rise' and 'Sun set' is caused by the Earth's rotation. I read that 'Sun light' takes around 8 minutes to reach ...
108 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 ...
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### Capability of observing transits with terrestrial telescopes of various sizes?

I have access to my university's telescope, Dearborn Observatory, an 18.5 inch refractor on the shore of Lake Michigan, just north of Chicago (yes, it's an atrocious location, but the telescope still ...
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### Is the Earth-Sun distance 1.012 AU?

Wolfram Alpha's query: Sun Earth distance in AU gives: 1.012 au (astronomical units) They definitely use this value in other places too - e.g. Earth-Sun $L_1$ distances from Earth and from Sun ...
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### Why can't our Sun be a binary with Jupiter as a T or Y dwarf?

I just learned about Brown Dwarfs, they are "failed" stars, they narrowly missed the stellar mass mark. I learned that Y Dwarfs have temperature as low as 80 Fahrenheit (The first one found by WISE ...
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### Why is there a gap in this image of supernova discoveries?

I came across this gif showing supernova discoveries from the late 19th century to 2010. Here's the data in 2010: Notice that there's a prominent region shaped like an inverted U in which there are ...
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### When will the next summer solstice and a full moon coincide? What day?

What day will the summer solstice and full moon coincide? As far as I know the next time will be in 2016. I would like to know what day.
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### How long do hot X-ray sources last?

Some X-ray sources in nebulae are caused by hot materials in the millions of degrees that formed in supernovae. What's the cooling rate of this stuff? How long does it stay this hot? I would expect ...
150 views

### Why does lithium fuse at lower temperatures than hydrogen?

This is a basic question, but it's been bugging me. In the Wikipedia article for lithium burning, it states that: Stars, which by definition must achieve the high temperature (2.5 × 10^6 K) ...
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### What is the temperature 55 km beneath the surface of Mars?

What is the temperature 55 km (34.18 miles) beneath the surface of Mars? The reason I ask is that I want to know if it might be habitable for a possible future colony if they could dig that deep (...
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### Percent-illumination of crescent moon and its naked-eye visibility?

What level of percent-illumination of moon (waxing crescent), given by Stellarium, is enough to make it visible with naked eye, in clear sky? thanks
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### If the universe keeps expanding, can we travel to the edge of the universe? [duplicate]

If the universe keeps expanding, is it possible to travel to the edge of the universe?
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### Can't we see all of the Milky Way's supernovae with the naked eye?

I found this on the Wikipedia page on supernovae: The total supernova rate in our galaxy is estimated to be about 4.6 per century, or one every 22 years, although we haven't actually observed one ...
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### How much of the Milky Way is visible to the naked eye from earth?

When we see the Milky Way on a dark night are we seeing the bulk of the galaxy, or just our local arm? How much of the milky way is visible to the naked eye on a dark night?
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### Sun from SuperNova

I have read that our sun was created from older star(s) which had exploded in a supernova. If all the matter is travelling away from the central point of explosion, how does it coalesce back into a ...