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13
votes
1answer
704 views

What is the current accepted theory as to why Mercury, despite its size, has a similar density to Earth?

According to the NASA web page overview about Mercury, despite the planet being just a bit larger than our moon, it's density is about 98.4% of Earth's. This high density suggests a comparatively ...
8
votes
1answer
340 views

Why has Moving Cluster Method been successful only for Hyades?

At all places where I have read of Moving Cluster Method for measuring distance to a cluster and once applied myself on data, I have been told that the method has been successfully applied only to ...
15
votes
2answers
17k views

Does the Moon have any oxygen in its atmosphere?

Since the moon has gravity, it's almost impossible that there aren't some gasses trapped on the surface by the moon's gravity. Has any free-floating oxygen been found on the Moon? If so, in what ...
15
votes
1answer
1k views

Have we ever observed a large meteor hit the Moon?

Since the moon has no atmosphere, its surface has many more meteorite impacts than Earth's does. Image source Have we ever observed a meteor strike the surface of the Moon?
9
votes
1answer
3k views

What is the origin of the OBAFGKM classification system?

Once a body has been identified as a star it is classified into a subsection of either O,B,A,F,G,K or M (I think there are also 3 more letters recently added) What is the origin of this ...
11
votes
2answers
529 views

Why does Mars appear to retreat across the sky?

If you plot the movement of Mars across the Earth's sky it appears to move back on itself during its orbit. Why does it appear to have a loop shape from Earth?
15
votes
1answer
508 views

If the moon wasn't receding from Earth, what would be the impact on the weather and tides?

Moon is slowly receding from Earth, which means that after its formation it was much closer to the Earth than now. How would weather look like if it wasn't receding at it would be now as close as at ...
13
votes
2answers
2k views

How does angular resolution of a telescope translate to its parallax precision?

We can often read in the scientific and also more casual reader literature and articles about the angular resolution of various telescopes and other optical equipment, be it ground based or onboard ...
29
votes
1answer
1k views

How could a hobbyist astronomer determine apparent magnitude of a star?

Apparent magnitude is a rather complex way to determine the brightness of a star. Quoting the introduction text from the linked to Wikipedia page: The apparent magnitude (m) of a celestial body is ...
22
votes
3answers
8k views

Is there a theoretical maximum size limit for a star?

Some stars are simply huge. Eventually, though, wouldn't there be simply too much pressure or mass for the star to sustain itself? Wouldn't it eventually collapse into a black hole? Is there a ...
21
votes
1answer
357 views

Dark Matter Particle Candidates

Dark matter appears to dominate the matter component of the universe as compared to luminous, or baryonic, matter. Though it does not interact electromagnetically (it doesn't absorb, scatter, or emit ...
32
votes
2answers
18k views

Why does Jupiter have so many moons?

Jupiter has a great many moons - in the hundreds, and they're still being discovered. What is the current theory for where all these moons came from? Are they rocks flying through space captured by ...
12
votes
2answers
599 views

Sky photography through compositing images in software?

I've read about and seen some rather sophisticated rigs for night sky photography that allow for ultra-long-exposure photos by counteracting the rotation of the sky by rotating the camera with it. The ...
17
votes
3answers
1k views

What is there in the intergalactic space?

What bodies can be encountered way outside galaxies - far beyond the farthest edges of galaxies, in the deep space between them? Are there single, galaxy-less stars, giant clouds of gas more dense ...
19
votes
2answers
665 views

Space expansion in layman terms

So far I got to understand the expansion of space is not to be understood as stars drifting further apart through space. There's something more fundamental - e.g. you can't simply measure speed of it, ...
13
votes
1answer
314 views

How fast do we travel through space?

Could someone give the rough estimates of speeds of our travel through space? I can easily find the two nearby ones: Earth's own rotation - depending on latitude, up to 40,075 km/24h = 463 m/s Earth'...
14
votes
2answers
1k views

What is the evidence that galaxies rotate?

Do all galaxies rotate? If so, do they rotate in the same direction? What observations have been made of galaxy rotation?
8
votes
1answer
232 views

What evidence is there of Earth-Like internal features of Europa?

This question is inspired by "What are the Earth-like features of Titan?". According to NASA's Europa overview, Europa is believed to have an iron core, rocky mantle and an ocean under the frozen ...
20
votes
1answer
4k views

Why do some planets have rings?

Some planets, specifically Jupiter, Saturn, Uranus, and Neptune in our solar system, have planetary rings. Why do some planets have rings? How are they made and from what? Most importantly, will I ...
13
votes
2answers
18k views

What is the current theory for the formation of the Earth's Moon?

Given that the Earth and Moon are often said in the literature to have very similar geochemistry, what is the current theory as to how the Earth's Moon formed?
21
votes
2answers
704 views

Why is the Hubble Telescope in space?

Why is the Hubble Telescope in space? Do we get enhanced clarity and range by placing it in space? What can it achieve from space that it could not achieve from Earth?
11
votes
1answer
996 views

What is a hypernova and have we observed any?

Inspired by the question "What does it mean for a star to go nova or supernova? Can I safely observe these?", I am curious about what hypernovas are? Have we observed any occurring, or the at least ...
18
votes
1answer
5k views

What does it mean for a star to go nova or supernova? Can I safely observe these?

What does it mean for a star when people say it goes 'nova' or super nova, what are the differences? More importantly, can I safely observe these with an amateur telescope? I imagine they would be ...
21
votes
4answers
29k views

Does the Sun belong to a constellation?

Each new star we find is generally considered to be part of the constellation it is nearest to. Our Sun is obviously a star, just much closer. Is our Sun part of any constellation? If so, which ...
5
votes
2answers
2k views

What are shooting stars and how are they formed? [duplicate]

What are shooting stars? How are they formed and how often do they occur during the night? Also, why are there more shooting stars on some nights than on others?
6
votes
2answers
2k views

What gases are needed to make a star?

What gases do you need to start the creation of a star, and why do you need these gases? What are their functions?
15
votes
2answers
163 views

How can we detect water on Mars-like exoplanets?

According to data from Curiosity, Mars' dust holds about 2% water by weight This wasn't previously detected, so the impression we have had of Mars being incredibly dry may need to be altered. Okay it ...
18
votes
3answers
2k views

Why can't we observe the Oort cloud with a telescope?

The Oort cloud is a hypothetical structure based on our observation of long-period comets. There are currently proposals to design probes to confirm the existence of the Oort cloud. Now, sending a ...
15
votes
4answers
11k views

How was the core temperature of the Sun estimated?

It was estimated that the heat inside the core of the Sun inside around 15 000 000 °C - this value is extremely enormous. How did scientists estimate this value?
14
votes
1answer
566 views

How do I build a stargazing aficionado's Sun funnel to observe our nearest star safely?

How do I observe the Sun safely, with tools I could build myself and without breaking the bank? If I wanted to build a Sun funnel on my own and use it on my enthusiast grade telescope, how would I do ...
12
votes
1answer
401 views

What is the significance of the discovery of a pulsar flipping between radio and x-ray emissions?

This morning on the radio I heard about the discovery of a pulsar that, due to its proximity to a companion star, was flipping between a state where it emitted radio waves and one where it emitted x-...
12
votes
2answers
697 views

How do stellar temperatures vary?

The temperature of the surface of the Sun (photosphere) is between 4500° - 6000° Kelvin. Inside the core, it's around 15.7 million degrees Kelvin. In other types of stars (neutron stars, white ...
24
votes
1answer
820 views

Why is the Sun's atmosphere (the corona) so hot?

The visible surface of the Sun is 6000 degrees Celsius but the gas in the solar corona is at least 1 million degrees. What heats the solar corona?
13
votes
2answers
255 views

Do any known exoplanetary/solar bodies have “annular” eclipses similar to Earth's?

This was somewhat inspired by this question but is a bit different: I am interested in if there are any known systems in which the angular size of the eclipsing object is almost the same as the ...
10
votes
1answer
182 views

What is the current routine of modern astronomy? [closed]

With about all visible stars catalogued, measured and photographed it seems that chapter is closed. I realize currently while amateur astronomy is big on cataloguing all asteroids in the Solar System, ...
12
votes
3answers
6k views

How does moonrise/moonset azimuth vary with time?

In my tenacious attempts to observe moonrise (surprisingly difficult in a poor weather heavily urbanized hilly area with frequent bad smog, with busy work schedule and a bicycle) I was frequently ...
13
votes
2answers
158 views

What azimuth description systems are in use?

For a time, I thought Azimuth is always direction in degrees, 0 for local, geographic north, 90 for east etc. Then, trying to observe moonrise I downloaded an app that gave azimuth in values between (...
21
votes
2answers
39k views

What is the formula to predict lunar and solar eclipses accurately?

A number of ancient civilizations had devised methods to predict exact dates and times of such eclipses, marking them as important events. Hence I assume the predictions were based on calculations, ...
15
votes
1answer
743 views

Why does the Moon seem larger when it is close to the horizon? [duplicate]

I've noticed that when I look into the sky at night, sometimes the moon appears very large near the horizon. Sometimes it also looks like it has a yellow tint. Is this the light rays bouncing off ...
7
votes
3answers
1k views

I'd like to become an astronomer. What experience do I need? [closed]

I think I'd like to become an astronomer. What degrees and training/experience do I need to become one? I've heard I should take science and mathematics, but I don't know which specific courses I ...
18
votes
2answers
2k views

Why do stars appear to twinkle?

Sometimes at night you will look up to the stars and they will appear to twinkle, getting brighter and darker in bursts. Why does this happen? Is this because of our atmosphere? Would they twinkle ...
18
votes
2answers
2k views

Do other planets in our solar system experience eclipses or is this unique to Earth?

Here on Earth we get to experience lunar and solar eclipses. Is this pure coincidence that everything happens to line up? Do other planets in the solar system experience this phenomenon or is this ...
11
votes
1answer
215 views

What is the relevance of the Tropics and the Polar Circles? Do they Exist on other planets?

The middle line is the equator, the second and fourth line are the tropics, the first and fifth are the polar circles. What is the relevance of these bands on Earth? Do these exist on other planets? ...
13
votes
2answers
169 views

Relativistic effects in stellar dynamical systems

I am curious, if anybody knows of any stellar dynamical systems/environments, where relativistic effects could play a dynamical role on the motion of these stellar systems? As a subquestion - are ...
15
votes
3answers
3k views

What is the difference between asteroids, comets and meteors?

Some celestial objects seem to be referred to as asteroids, some as comets, and some as meteors or meteorites. What is the distinction between all of these different objects? Are any of them the same?...
19
votes
2answers
1k views

What physical features determine if a planet is a major, minor or dwarf planet?

Like many, when I was growing up, we always were taught, hence always learned that there were 9 planets. However, recently, decisions were made and all of a sudden there were 8 major planets and a ...
13
votes
1answer
364 views

How is it known that Callisto has no core?

My Astronomy book claims that scientists have discovered that Callisto, a moon of Jupiter, has no hot inner core. In fact, it says, Callisto has a core much like the nucleus of a comet. Is this still ...
21
votes
2answers
562 views

Near-Earth supernova

There are 51 stars within 17 light years of the Earth (source). If one of these stars was to become a supernova, how would they effect the Earth?
11
votes
1answer
508 views

What is the current accepted hypothesis of what caused Triton's retrograde orbit around Neptune?

According to the NASA overview about Triton, this, the largest satellite of Neptune is unique in that it has a retrograde orbit around Neptune. The page also suggests that Triton is a captured Kuiper ...
14
votes
1answer
978 views

Why does the moon sometimes appear giant and a orange red color near the horizon?

I've read various ideas about why the moon looks larger on the horizon. The most reasonable one in my opinion is that it is due to how our brain calculates (perceives) distance, with objects high ...

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