# Tag Info

## Hot answers tagged naked-eye

92

The answer is yes; for a few nights prior to the impact (assuming they had eyes with a similar sensitivity to our own and could look up!). It could also be much longer than this if the object was a cometary body. Details: Impacting solar system objects would have relative closing speeds from around 11 to 72 km/s. We could take the optimal case that the ...

68

Yes and no. Yes, it's true that the apparent size of the Moon is 30 arcmin. It's true that the visual acuity of most people is 1 arcmin. So it's true that if you take the angular size of the smallest detail you can see on the Moon, and you put a bunch of those lined up straight in a row, you could span a Moon diameter with only a few dozen of them. In that ...

54

It doesn't seem so far-fetched to me. Sure, you might be off by a few pixels, due to differences between the human eye and a computer monitor, but the order of magnitude seems about right — the detail in your images, viewed closely, more or less matches what I see when I look at the full moon. Of course, you could fairly easily test it yourself: go ...

38

Well, there's two things we'll need for this: apparent magnitude (the brightness that an object appears to have) and absolute magnitude (the actual brightness an object has). Both of these scales are logarithmic, with brighter objects being lower and dimmer objects being higher. Astronomers have determined that the Sun's absolute magnitude is 4.83. Knowing ...

32

Glancing at a partial solar eclipse is about as dangerous as glancing at the Sun on any other day. If you look at the Sun a few minutes after sunrise or a few minutes before sunset, when the Sun's altitude is low, the light is filtered through a lot of air, and most of the ultraviolet is scattered, so it's a lot less dangerous than looking at the Sun in the ...

29

No, it cannot. Far from it. The closest approach between both planets is roughly 16 AU due to the 3:2 orbit resonance. Pluto will even then be a tiny dot among many with a brightness around 14 mag. You can try that with Stellarium yourself, placing the observer on Neptune and looking for Pluto. You just have to find the right time. One such time is approx. ...

22

When you gaze at the moon "live", you are not seeing a still image. You're seeing a "video": your retina is gathering multiple images over time. Those pixels have to be taken into account; they amount to extra pixels. Suppose that 60x60 pixel images are taken of a scene using a tripod-mounted camera which slightly jitters. From the multiple images, a higher-...

14

In the best sky conditions, the naked eye (with effort) can see objects with an apparent magnitude of 8.0. This reveals about 43,197 objects in the sky. There are 9 galaxies visible to the naked eye that you might see when observing the sky, and there are about 13 nebulae that you might see. Sources: The Bortle Dark-Sky Scale - John E. Bortle How many stars ...

14

According to the NASA Pluto fact sheet, the brightest that Pluto gets is an apparent visual magnitude of 13.65 when it is 28.6 au from the Earth and (presumably) about 29.6 au from the Sun. To work out how bright that would be from Neptune we could work out how close Neptune can be to Pluto when Pluto is at perihelion. This is complicated by the fact that ...

13

Well, having seen Neptune and identifying Neptune are two totally different things. Let's tackle this one step at a time. Your link says: From these observations it would appear that, if seen upon a perfectly black background, a star of magnitude approximately $8.5$ would be at the limit of unusually good vision. The problem with this is that there are ...

13

I'll add to Wayfaring Stranger's comments. In fact most of the time you would be able to see fewer stars in the night sky of Mars, than in a good dark night sky on Earth, because of dust obscuration. Even in favourable conditions, the optical depth of the Martian atmosphere is usally somewhere between 0.5 and 1 per airmass. (Petrova et al. 2012; Lemmon et ...

11

A carbonaceous condrite has the same reflectivity as the moon at around 7-13%. If there was ice, if the tail was 10 times smaller than Hale-Bopp, it would have auspiciously covered half of the sky. it could have made an incredible display in the 1-2 days preceding the collision, because it was as close to the sun as Hale-Bopp, the brightest astronomical ...

11

This webpage gives a lot of background information. Key points: It does seem to be the overall dimness of near-total eclipses that allows the pupil to widen enough to allow damaging levels of UV in. There are cases of eye damage from staring at the full sun, and also cases of staring at the noonday sun without apparent damage (not recommended). Perhaps ...

8

You can tell a lot about Galactic structure by just looking. The ~5000 stars that can be seen with the naked eye have a roughly "lognormal" distribution of distance. I show plots below which were generated from the most recent version of the Hipparcos parallax catalogue. Fig.1 shows results for all stars with $5.5<V<6.5$ (i.e. very faint naked eye ...

8

First Shooting Star Seen from Mars space.com 2005 The background image shows the meteor near the top-left and the horizon at the bottom. A red arrow shows the direction of travel. The inset is a larger version of the meteor itself. The graph is a "light curve" that aided in tying the meteor to comet Wiseman–Skiff. (Image: © Nature/NASA/Spirit/F. ...

7

There is an article here that describes the visible effects quite well. In essence, within a week or so, it would be comparable in brightness to the moon and therefore visible during the day. Betelgeuse would then start a phase of final, rapid dimming and again reach its current brightness level after possibly three years. After six years, it would be ...

6

The apparent magnitude classification was done arbitrarily by Ptolemy. His thought was to set the 20 brightest stars to the first position, the less bright stars to the second position and so on up to the faintest stars which were given the sixth position. After the use of Pogson's law we were able to give to stars not only natural numbers, but also numbers ...

6

The resolved stars (those that can be seen as individuals) are all part of the Milky Way Galaxy (unless there are any interlopers that have been captured!). The distances to the next nearest galaxies of any size are more than 100,000 light years. Andromeda is 2 million light years away. Unless one goes supernova, there basically aren't any types of star ...

6

We have pictures of this, thanks to Curiousity! (Source) “A human observer with normal vision, if standing on Mars, could easily see Earth and the moon as two distinct, bright “evening stars,” said NASA in a statement issued today. So yes, you can see our moon from Mars. The apparent brightness of our moon from Mars is +0.9. The apparent brightness of ...

6

Taking Mars' average distance from the sun of 1.52 AU, the sun would be 43% as bright. Phobos has an albedo of about 0.071 which is pretty dark. Darker than the Moon with an average albedo of about 0.12, so it reflects about 59% as well as the Moon does. That gives it a brightness to area of just over 25% the brightness of the moon. Phobos is an odd ...

6

The aurora depicted in the artist's conception is of ultraviolet light. It would not be seen with the naked eye. "NASA's Hubble Space Telescope observed a pair of auroral belts encircling the Jovian moon Ganymede. The belts were observed in ultraviolet light by the Space Telescope Imaging Spectrograph and are colored blue in this illustration. They are ...

6

Light rays travel along things called geodesics in spacetime (specifically they travel along a certain class of geodesics called 'null geodesics'). If spacetime is flat, which will be the case in the absence of gravity, then those geodesics are just straight lines as we normally think of them, and so yes, light rays travel along straight lines in that case. ...

5

Alpha Centauri A and B happen to be rather similar to Sol, and their absolute magnitudes are 4.38 and 5.71 respectively (Wikipedia). Add them together and you get absolute magnitude 4.10 (the scale is logarithmic, and backward). Sol, with absolute magnitude 4.83, should look 0.73 magnitude dimmer than αCen at the same distance, so magnitude +0.46, ...

5

In theory, yes; in practice probably not ... i) It's perhaps helpful to take the Andromeda galaxy as a first working example. It is somewhat bigger than our own Milky Way galaxy but not so big as to be a problem. When we look at Andromeda, it appears to occupies an area about 3 degrees by 1 degree. By comparison, the Moon appear about 0.5 degree across. ...

4

Depending on your eyesight, the faintest stars you can see in a perfect environment have an apparent magnitude (brightness) of 6-6.5 (though some people have managed to see magnitude-7). According to this site, that translates into about 10,000 stars. As for how it would look, I have seen the sky from the stratosphere (about 3 miles up, in a plane, where ...

4

There is a rule about average surface brightness: it is conserved as you change distance or magnification. For the gory details see. Telescopes make unresolved objects brighter, but for resolved objects, a telescope shows you the actual surface brightness (assuming that the exit pupil diameter is well matched to your eye's pupil (~7mm) and is not throwing ...

4

Because light with higher frequency, that is bluer colors, scatters more in Earth's atmosphere and celestial objects thus look redder (yellow is towards red) while the atmosphere looks blue. See Rayleigh scattering. Here is video with a lengthy and somewhat entertaining explanation: https://www.youtube.com/watch?v=SRh75B5iotI

4

After all these astronomic answers, I will add a computer one. Pixels are not the same on all monitors. Take a 1990's monitor and take the latest smartphone screen, the 60 pixels won't be the same. How did you calculate the pixel size according to the vision accuracy ?

4

The key to this is the so called Absolute Magnitude, which represents the visual magnitude from a distance of 10 parsecs (about 32 light years). The sun is much brighter than Proxima Centauri. It has an absolute magnitude of 4.8, and at a distance of 4 light years (the distance of Proxima), it would be be somwhat brighter than 1st mag, and so very easily ...

4

Light will travel in a straight line through the 4D Space-time continuum. It does not wiggle around and is only deflected by gravity. Light from distant stars reaches us more or less parallel due to the great distance involved. But depending on how accurately you wish to make the measurement, there is scope for some light from that star to reach us very ...

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