Hot answers tagged

52

No, because Mars can't have eclipses. Strictly speaking, Mars has only transits. The difference is that Mars's moons are smaller than the Sun as viewed from Mars, thus they don't block out the entire sun. Eclipses are defined as only occurring if the entire sun is blocked, or at least the vast majority. Phobos blocks out only about 60% of the sun at most. ...


35

We can look at what happened when this actually occurred. The geomagnetic storm of March 1989 was caused by a Coronal Mass Ejection. Here are just a few of the many effects on satellites. One satellite lost 3 miles in altitude (not 30 km! don't believe that legend). Another began uncontrolled tumbling. GOES 7 lost communications and imagery for a time. ...


32

Looks pretty darned quiet to me right now: You can find that here, along with other measures of space weather. By the way, cosmic rays and solar activity are two entirely different things. Cosmic rays originate from outside of our solar system. The flux of cosmic rays is relatively constant. As for your question about stress, indeed, I just experienced ...


31

I spent a couple of years working in the Astrophysics and Space Physics Section of JPL. Working with the Space Physics folks taught me a lot about the solar wind and other space weather phenomena. Later on, working with Hank Garrett of JPL's Space Environments group taught me more, especially concerning effects on spacecraft. I'll start out with a ...


31

Addressing is the sun's mass and other quantities known well enough for this to be absolutely accurate? Well, the key to this is the vis-viva equation in your question. It's not actually important for us to know the mass of the Sun precisely, so long as we know the product $GM$ (another answer makes mention of this). And that product is, of course, the ...


29

No, not yet. The Parker Solar Probe became the closest ever artificial object to the sun on October 29th, 2018, surpassing Helios 2 which held the record since 1975 [1]. No other human-made object has been closer to the Sun. The probe will repeatedly touch the outer corona until mission end in 2025, with the closest approach being 3.83 million miles [2]. It ...


28

You can find the image on Flickr. On August 31, 2012 a long filament of solar material that had been hovering in the sun's atmosphere, the corona, erupted out into space at 4:36 p.m. EDT. The coronal mass ejection, or CME, traveled at over 900 miles per second. The CME did not travel directly toward Earth, but did connect with Earth's magnetic ...


28

As noted in another question, the ISS faces some pretty hot temps. Remember, the Sun heats radiantly. When you're sitting in that much radiant heat, without an atmosphere to dissipate it, you're going to get hot really quick (emphasis mine) Without thermal controls, the temperature of the orbiting Space Station's Sun-facing side would soar to 250 degrees ...


24

The Vis-viva equation is $$ v = \sqrt{ GM \left(\frac{2}{r} - \frac{1}{a} \right) }, $$ The $GM$ product for the Sun is 1.327E+20 m^3/s^2. If 1 AU is 150E+09 meters, then when you are in a circular ($r=a$) Heliocentric orbit at Earth escape/capture point your velocity is 29.7 km/s. If you then change to an ellipse with aphelion still at 1 AU and ...


23

I suspect you mean objects that haven't left the solar system (and what is the boundary?) and that aren't orbiting another planet. Every object en route to another planet that has left the Earth's sphere of influence and has not yet entered the target planet's sphere of influence is orbiting the Sun. Whether the Pioneer 10, Pioneer 11, Voyager 1, and ...


23

The sun is not "burning" in the sense you are used to: there is no chemical reaction going on. Instead, there is a very high pressure in the core of a star (like our sun) due to the high mass that starts/sustains a nuclear fusion process. In our sun, hydrogen is fused to helium and the energy that's released in this process is what makes the sun "glow" and ...


22

While the solar corona is very hot, it also has very low density: Wikipedia gives a ballpark figure of about 1015 particles per cubic meter, which, at 1 million Kelvins, translates to a pressure of about 0.01 Pa. That's a pretty good vacuum, comparable to that in low Earth orbit. The low pressure means that the coronal plasma doesn't hold much heat that it ...


22

The closer an object to the source of light, the larger the shadow it casts. That's true if we're talking about a point source or at least a compact source of light and "shadow" refers to the "umbra" or area of complete shadowing. But it no longer makes sense in this case where seen from Earth the obscurer (spacecraft) is tiny compared to the "obscuree" (...


18

In addition to the definition given by David H, I would add Ulysses, which is specifically observing the sun from out of the plane of the ecliptic and might mean what the questioner is asking for. Ulysses made two passes around the sun, one over each pole, and its mission is officially over after the second pass. In order to get out of the plane of the ...


16

Solar Probe, planned to launch in 2018, will get to within 8.5 solar radii of the Sun's surface. For comparison, Mercury gets no closer than 65 solar radii. Solar Probe will use a thick carbon-carbon, carbon foam shield when in close proximity. The record so far is held by Helios-2 in 1976, which got just inside Mercury's orbit at 0.29 AU, about 61 solar ...


14

Spacecraft Overview: "preliminary designs include an 8-foot-diameter, 4.5-inch-thick, carbon-carbon carbon foam solar shield atop the spacecraft body..., radiators for the solar array cooling system, ... actively cooled solar arrays". Low albedo for the heat shield isn't mentioned explicitely. A highly elliptical orbit leads to relatively short periods of ...


13

Getting hard numbers about how accurate measures we can get from current systems, adapted to the Sun instead of far away stars is difficult, bordering to impossible. But we can get data about the relative difficulty of the solar system planets. First off, we can do some cheating for Mercury and Venus, as they occasionally go in front of the Sun. Given your ...


13

Thermodynamics says there's no such thing as a completely internal cooling system. The best you can do is pump heat to a cooler location. That's very difficult to come by in the photosphere. Besides trying to keep cool enough for some alloy to remain solid, keeping electronics or a power source cool enough to function would be significantly more difficult....


13

I'm posting these images as a supplement @Hobbes's accepted answer and @TildalWave's comments (which includes links to these images). I started reading some of those links. The gallery is a good starting place but there are different tabs to check out. The values 171 and 304 represent the central wavelengths used, in Angstrom units. Our visible spectrum is ...


13

Insulation can function in both ways, keeping heat on whichever side is desired. In space limiting the amount of thermal input from the sun is very valuable since that heat is easily acquired but hard to get rid of.


13

If you're already in a solar orbit, then yes. You can use a sail at an angle and send the reflections prograde. The result is to reduce your orbital energy and you spiral in. I recall it was a standard physics problem to find the angle that maximized the energy transfer (it's not 45 degrees). Time of journey depends on the mass of your item and the ...


12

The video is significantly sped up (videos of the Sun generally are sped up). CMEs move at an average speed closer to 500 km/s. That's why when we see the activity we generally have a warning of up to a few days before the CME gets to where we are. If the CME was moving at the speed of light, it would hit us as we saw it happen (a little more than eight ...


12

What would happen? Not much. The Sun is mindbogglingly vast. Even our biggest nuclear bombs don't fuse more than 1 ton of hydrogen. Compare that with the Sun's 620 million tons burned per second: the nuke would add $10^{-9}$ to the Sun's output.


12

Acceleration due to gravity is given by $$ a = \frac{GM}{r^2} $$ where G is the universal gravitational constant, M is the mass of the central body and r is the distance between the bodies' centers. For Jupiter at ~5.2 AU average orbital radius, this works out to 0.22 mm/s$^2$. This is $2.2\times10^{-5}$ (or 0.000022) times the gravitational acceleration ...


11

As a reference, part of this question I answered at Astronomy.SE. The closest point at which the Sun would not be the brightest object in the sky is if we headed directly towards Sirius A, at a distance of 1.46 light years. The fastest object leaving the Solar System right now is Voyager 1. It's speed right now is about 38026 miles per hour, or about 5....


10

Voyager 1 took an image of the sun on February 14, 1990 at a distance of 6 billion kilometers. The famous Pale Blue Dot was captured at the same time and is superimposed here as well as a narrow angle view of Venus. This color image of the sun, Earth and Venus was taken by the Voyager 1 spacecraft Feb. 14, 1990, when it was approximately 32 degrees above ...


10

There is oxygen and many other elements on the Sun. The "burning" you refer to is fusion, it does not require oxygen. Oxygen is created by: 12 C + 4 He ------> 16 O + energy. In case you are wondering how the carbon for that reaction is created it comes from: 3 (4He) ------> 12C + energy, with the helium derived from: 4 (1H) ------> 4 He + 2 e+ + 2 ...


10

You are missing something basic here, which is that the Sun's corona is rather sparse. To take matters to an even greater extreme, consider the intergalactic medium. The temperature of the extremely sparse intergalactic medium can be in the hundreds of millions of kelvins. However, a macroscopic thermometer in this hot medium would not get anywhere close to ...


10

It's a "real number", a delta-v chart isn't really concerned with the realism of various missions. It's quite simply a table of velocity changes, how you would go about achieving these velocity changes is outside its scope. As to how to calculate it, the parts of the journey in space can be calculated like any other part of the diagram, using the patched ...


9

Every Apollo mission sent to the moon was a roll on the dice praying like hell that a major solar flare wouldn't be sending an ejection Earthside. This is why NASA didn't raise that much of a fuss when the last 3 missions were canceled. As demonstrated in the movie "Space" the Lunar Module would have provided no protection whatsoever. The Command ...


Only top voted, non community-wiki answers of a minimum length are eligible