I’m imagining pretty huge…and incredibly hot. I wish I could visualize what it’s like to experience a sunrise, day, and sunset on Mercury. (Suitably protected, of course… SPF Google)
I’m fascinated by views of objects in our solar system from unusual locations. I’ve seen the view of Earth from Mars, the (simulated) view of the sun from Pluto, and the APOD pic of all the planets seen from Voyager(?) anyone know of other websites with this kind of stuff? There was one website with pictures of artificial satellites taken from ground-based telescopes, but I’m unable to find it now.
What the h*ck? The last sentence at that link says “That is why the time interval between two successive noons (when the Sun is highest in our terrestrial sky) is only 23 hours and 56 minutes”
I know the equation of time makes the time of high noon inexact, but it is still closer to 24 hours, than it is to the sidereal value of 23 hours and 56 minutes.
[quote]
In December, near the northern winter solstice, the interval between successive noons is about 30 seconds less than 24 hours. Because this difference is greater than the daily change in sunrise and sunset times, it becomes the dominant effect, causing the observed separation of the dates of earliest sunset and latest sunrise.
A similar effect is seen in June, but the interval between successive noons, is then only about 13 seconds less than 24 hours, so the dates of earliest sunrise and latest sunset are closer to the summer solstice–the longest day Definitely nowhere near a difference of 4 minutes.
The average value is 24 hours, so it can’t be shorter both in December and in June. In December, it’s more, not less. That’s the equation of time, I mentioned before.
Also, at the bottom of that link, it says that this effect is “Mainly because the Earth’s axis is tilted with respect to its orbit around the Sun.” Actually, that’s only half the story. The other half is the eccentricity of Earth’s orbit–it moves faster during December and January because it is closer to the Sun, and the rotation has farther to go to catch up, to have the Sun appear directly overhead.
Today (Feb 21), the sun has an angular diameter of 1.22 degrees when viewed from the surface of Mercury. Here’s a picture of it. You can create similar pictures from the surface of any planet here.
Yes, it can. The time between successive noons doesn’t go through a single cycle (with a maximum and minimum separated by six months) in a year, but a double cycle with two maxima and two minima. At both solstices the sun’s apparent motion is due west (parallel to the projection of the equator onto the sky), so it can make a circuit of the sky faster than at other times of the year, when it is moving a bit north or south of due west and only a component of its motion is in a westerly direction.
That is a very cool site, Squink. Unfortunately though, the picture it produces is zoomed. So when you do a picture of the sun from Earth it looks the same diameter. In fact, same thing with Pluto.
According to this site, you’d have to hang around for a long time, since Mercury rotates on its axis very, very slowly. From one sunrise to the next takes 176 earth days!
Mercury has a rotation period of 58 earth-days and an orbital period of 88 earth-days. This translates to Mercury’s days being longer than its years. One day on Mercury lasts 176 earth-days or 2 mercurial-years.
There’s a radio button that lets you choose to take up a certain percentage of the field of view, OR see the object in a view that is a specified number of degrees across.
That site is way cool but I had to use Explorer to get all the prompts (Netscape doesn’t work, help?). I didn’t realise Titan would be so big in Cassini’s view at this point.
Check out the Equation of Time. As Drogulus says, it’s decreasing both in June and in December, and increasing in September and March. Anyway, that first link clearly wasn’t thinking of the Equation of Time. They got confused; if they hadn’t, they would have said successive noons are exactly 24 hours apart.
Argh. I knew that. I checked the December figure and found they had it wrong, and didn’t even check the June one, didn’t even think about it. My mistake, thanks for the correction.
That’s backwards, idnit?
www.analemma.com has the effects of the tilt, and the Earth’s eccentricity quantified. The effect of the eccentricity is as I mentioned, but the tilt is what gives the equation of time the double hump character, and at the soltices it is slower–it takes longer each day to go from noon to noon.
Yup. i was also mislead by the figures in New Scientist. The sun’s apparent motion is toward the west, but the component of it that’s due to the earth’s motion around the sun is due east at the solstices and makes the noon-to-noon interval longer at those times.
Thanks Eleusis. As a math major, I knew that, but day to day I have a lot more interaction with Google ™ than with googols or their plexy cousins, so the two homophones have rather merged in my head.
Squink - thanks for the link; that’s exactly what I wanted. If I want to see the sun or other bodies *as I would see them with the naked eye were I standing on the surface of Saturn (I know, I know…), to what should I set the field of view?
