# Tag Info

9

Unless the stars comes so close that they actually collide, two stars will not be able to catch each other gravitationally. The reason is energy conservation: As they approach each other, their potential energy is converted into kinetic energy, increasing their velocities. When they are closest, their velocities are at their highest, but since there's ...

6

You don't have to guesstimate to come up with the answer. What you do is look at the dynamics of stars with respect to the Galactic plane - in particular, the velocity dispersions of stars with known distances from the plane, combined with a reasonable assessment of where the Sun is with respect to the plane (close), yields an almost model-independent ...

5

Yes, you are right. We don't only see the Sun 8 minutes in the past, we actually see the past of everything in space. We even see our closest companion, the Moon, 1 second in the past. The further an object is from us the longer it's light takes to reach us since the speed of light is finite and distance in space are really big.

3

Very roughly: $3.5 \times 10^{33}kg$, or 1800 solar masses. Here's how I came by that number, it is a very rough approximation. The major mass components of the galaxy are stars, the interstellar medium, and dark matter. According to the HYG Database there are approximately 1000 stars within 50 light years of the Earth. The average mass of a star is ...

2

Does the Sun turn around a big star? No. Such a star, if it existed, would easily be the brightest star in the sky. You would have been taught about it early on in school if it existed. But it doesn't. For a while it was conjectured that the Sun had a small companion star to explain a perceived periodicity in mass extinction events. This too has been ...

2

The Sun is not within the gravitational sphere of influence of any other star. The centre of mass of the solar system (which is very close to the Sun) instead orbits in the general Galactic gravitational potential. Because this has a roughly cylindrical symmetry (the Galaxy is basically a disk with a bulge in the middle), this means that it executes a ...

2

As it gets older, the core of the Sun starts to fill with Helium ash. This increases the average mass per particle and hence the core temperature must increase to maintain the pressure. This increases the nuclear reaction rate and the Sun becomes more luminous, at almost a constant surface temperature. The habitable zone is controlled not only by the ...

2

The gravitational effect of the planets on the Sun can be calculated very accurately. The acceleration of a planet of mass $M$ at a distance from the Sun of $r$ is $$a = \frac{G M}{r^2}.$$ If you plug in the numbers, you'll find that the largest effect comes from Jupiter due to its enormous mass. The gravitational acceleration of Jupiter on the Sun is ...

1

Yes, you *can *assign a temperature to the radiation from the Sun. It is approximately a blackbody radiation field with a temperature of 5800 Kelvin. But no, it doesn't "cool" on the way to the Earth. The radiation field is still a blackbody radiation field with a temperature of 5800K when it reaches the Earth, but its intensity (or power per unit area) has ...

1

The Sun's radiation spectrum is close to thermal at $T_\odot = 5778\,\mathrm{K}$. That means that that power output, given by the Stefan–Boltzmann law, is around $L = \sigma A T^4$, where $\sigma = 5.6704\times 10^{-8} \,{\mathrm{W}}/{\mathrm{m}^2\mathrm{K}^4}$ is the Stefan–Boltzmann constant and $A$ is its surface area: L_\odot = \sigma(4\pi ...

1

One billion years into the future and the Sun has swollen in size and it is now not possible to live on Earth due to the heat. The problem isn't so much the Sun swelling in size. The key problems are that the Sun's luminosity increases over time and that the Earth is covered with oceans. The Earth will become uninhabitable long before the Sun turns into ...

1

The Sun is not dying when the Earth supposedly becomes uninhabitable, it is just getting hotter as it evolves on the main sequence (core hydrogen burning, the Sun has something like 5+ billion years before reaching the red giant stage of its evolution)). It will continue to get more luminous and at a guess if Mars could be made habitable it would remain so ...

1

The answer by Florin Andrei comprehensively explains scientific and Earth based observation support for the heliocentric model. If we include interplanetary probes in the discussion, then yes, we have observed the Earth [orbiting] the Sun. In order to receive commands from controllers on Earth the probes track (read calculate and observe) the location of ...

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