Astronomy Stack Exchange
Astronomy Stack Exchange

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1500 questions
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Loss of atmosphere on Mars

If the atmosphere on Mars was once much thicker, how was it likely lost? Was it due to interaction with the solar wind, the small size of the planet, both, or something else, and approximately how long did it take to reach its current thickness?
Becky Ericson
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How did scientists determine an estimate of the number of planets greater than Sedna's size to exist in the Inner Oort Cloud?

In the article, New Dwarf Planet Found at Solar System's Edge, Hints at Possible Faraway 'Planet X' (Wall, 2014) where they report on research and observations performed by astronomers that discovered the dwarf planet 2012 VP113 which is smaller…
user2449
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How to identify stars in photographs?

I can look at a star chart and identify things like constellations in the sky. But if I take a picture with my DSLR camera (35mm with a decent zoom lens, no astronomy specific optics), I run into difficulty. I find that the camera can see a lot…
Michael
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Where does the Milky Way end?

I was reading this article and it says the following: Researchers measured the mass of the Milky Way and found that our galaxy is approximately half the weight of a neighbouring galaxy known as Andromeda which has a similar structure to our own.…
SpringLearner
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How does a gravity slingshot actually work?

From what I know of elliptical orbits, an object speeds up near the periapsis and slows down at the apoapsis, much like we learned in high school physics how a sphere would roll down and back up a valley in a frictionless vacuum: The height is…
Ky -
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How many stars can stay close to each other without collapsing?

Is it possible for two stars to exist close to each other? "Close" is relative; let's assume that two stars are close to each other if they are at the center of the same solar system. It's possible for this to happen with 3 stars. But what about…
Zoltán Schmidt
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How do I know it is safe to remove eclipse glasses when viewing a total solar eclipse?

I know this sounds like a really stupid question. But since I have never seen one or even used solar eclipse glasses I assume when I can no longer see the sun through the glasses then it is safe to remove them in order to see the sun's corona. OR…
Sedumjoy
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Error in "Efficient Method for Calculating the time of Sunrise and Sunset" by Robin G Stuart

I've been implementing this paper in python. "Efficient Method for Calculating the time of Sunrise and Sunset" by Robin G Stuart. The sun's equation of centre is incorrect no matter what I try. it's $\nu - M = 0.3342 \sin (l + 1.3450)$ where l is…
stanri
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Why did Chandrasekhar use 2.5 for molecular weight in 1931?

I understand that the history of the Chandrasekhar limit is complicated (see, for example, Edmund C. Stoner and the Discovery of the Maximum Mass of White Dwarfs, Michael Nauenberg, JHA 39:297, 2008 / PDF) but what puzzles me is the physics rather…
Leos Ondra
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How hot can a planet be?

Given that some exoplanets, particular "Hot Jupiters", orbit very closely to their parent star, how hot can these planets become? What is the hottest exoplanet discovered so far?
user8
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Non-anthropic, universal units of time for active SETI

Is there a universal time (duration) reference, an intuitive focal point that works for long periods (compared to the Planck time), and can be used as a signal of intelligence? Assuming a Kardashev Type III-level civilization can construct its own…
2080
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Why are almost all modern telescopes reflectors?

I've noticed lately that reflector telescopes are used much more than refractors. The majority of telescopes I see in telescope shops or featured by people online are reflectors. Even the Hubble and JWST are reflector telescopes. Is the reflector…
chowder
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Do planets lose energy while rotating?

When a planet rotates/spins, is it true that the planet loses energy? If this is true, then where does this energy lost by the planet go? My confusion may be in the basic understanding of the mechanism. When I imagine a planet rotating, what I think…
apk
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How can a brown dwarf be more massive than a star?

SDSS J0104+1535 is about 90 times more massive than Jupiter, making it the heaviest known brown dwarf. EBLM J0555-57Ab has a mass of about 85.2±4 Jupiter masses, or 0.081 Solar masses. I am confused. How is a brown dwarf more massive than a red…
Binita Rimal
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What is this 877-year cycle in the orbits of Jupiter & Saturn, and this multimillion-year cycle in the lunar orbit?

The book The Theory That Would Not Die (by Sharon Bertsch McGrayne, 2011) states the following on page 28: He [Pierre-Simon Laplace] used other methods between 1785 and 1788 to determine that Jupiter and Saturn oscillate gently in an 877-year cycle…
r.e.s.
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