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Have a look at this article. It gives the number as $10^{24}$ rather than $10^{23}$, but it's such a vague estimate that a factor of ten is within the expected error. The number is the number of stars in the observable universe i.e. within 13.7 billion light years of Earth at the time the light we see today was emitted. Note that visible means visible to a ...


4

I did some research and I think I can answer my question myself now, after all. I hope you find it interesting. As it turns out, the technology of the Kepler space telescope would indeed allow detection of all Solar system planets except Mercury and probably Mars, i.e. all of them are big enough to be seen by it from a distance of about 2,000 ly. However, ...


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This is just an opinion, but the moon on the horizon is simply less visible than the sun is. I suspect that color changes it makes are more subtle and less easily noticed. However full moons are often noticeably orange. Here is a page with a wonderful time lapse view. http://www.pikespeakphoto.com/moon-rising.html


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For the eye, draw a picture. You have an isosceles triangle with the small angle one arc minute and base 10 AU. What is the altitude? Bisect the small angle and you have two right triangles. For the second, you need to compute the small angle of the same triangle from the diffraction limit on a diameter of 2.4 meters. Can you find that equation in your ...


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Here are the systems I found: 6: ADS 9731 Beta Tucanae Gamma Velorum Kappa Tauri Mu Sagittarii 7: AR Cassiopeiae Nu Scorpii ... no physical multiple stars of greater multiplicity yet found.


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But I've never seen that happen. You haven't looked then. The rising or setting Moon is rather reddish, just as is the rising or setting Sun. However, there is a difference between the Moon and the Sun. You can look directly at the Moon, even a full Moon, regardless of where it is in the sky. On the other hand, you can only glance at the Sun when it is ...


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Answer to your old question: Right now, the perihelion currently occurs around the same time as (2 weeks after) the northern winter solstice, but 10000 years from now it will occur around the northern summer solstice. So, like other people have said, it's just coincidence that right now they both happen at about the same time. Answer to your new question: ...



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