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view of the Sun (APOD 21 May 2008)
Posted: Wed May 21, 2008 7:53 pm
by Mac Coak
Would our Sun look that big if viewed from Mercury? Mac
Re: APOD 05212008 view of the Sun
Posted: Wed May 21, 2008 9:03 pm
by henk21cm
Mac Coak wrote:Would our Sun look that big if viewed from Mercury?
Suppose the image
APOD 2008-05-21 was taken by a 35 mm camera with a 50 mm lens. The vertical angle the camera would cover, would have been ≅ 25°. If you look at the image, and estimate the portion of the image the red dwarf is filling, it is nearly the entire vertical range. So it is of the order of 20°. When standing on Mercury, which is about three times closer to the sun than the earth, the sun will look three times larger than on earth: ≅1.5°: a factor 10 smaller than the red dwarf.
If todays APOD represents the image an astronaut would see, in stead of a camera, the red dwarf might seem to be even larger.
So, the answer is No.
Posted: Wed May 21, 2008 10:20 pm
by apodman
APOD description mentions "gravitational tides".
Is there another kind?
Posted: Wed May 21, 2008 10:59 pm
by Arramon
This picture is so awesome... helluva job done by the artist. =)
*background image set*
Posted: Wed May 21, 2008 11:02 pm
by astrolabe
Hello apodman,
Yes, there are centrifugal tides.
Posted: Wed May 21, 2008 11:18 pm
by Arramon
http://www.waterencyclopedia.com/St-Ts/Tides.html
The Moon is held in orbit with Earth by Earth's gravitational force. There is also a centrifugal force pulling the Moon away from Earth and trying to send it spinning out into space.
Earth and the Moon rotate around the common center of mass of the Earth-Moon system; this system is held in orbit by the Sun's gravitational attraction while centrifugal force pulls the center of the mass away from the Sun. Both forces, gravitational and centrifugal, must reach and maintain equilibrium to hold the Earth-Moon system in orbit.
In the Earth-Moon-Sun system, the mass of the Sun is greatest, but its extreme distance renders its gravitational pull nominal. The tidegenerating force of the Moon and Sun vary as the inverse cube of their distances from Earth. The mass of the Moon is very small by comparison, but it is considerably closer, and therefore has a greater attractive effect on water particles than does the Sun.
Posted: Thu May 22, 2008 2:06 am
by astrolabe
Hello Arramon,
For the sake of clarification whenever we see a representation of the Earth's tides there is usually depicted a bulge on both sides of the globe. One is the lunar tide and the other is due to the centrifugal force of Earth's rotation.
The sun does of course play a role and tide charts far in advance can be calculated because of ephemeral info as well as other info like the natural "slosh" of the oceans, currents and seasons. Storm systems can change these criteria dramatically.
Posted: Thu May 22, 2008 4:24 am
by iampete
Very impressive picture - Ms. Nielsen is a talented artist.
Does anyone have any idea what the "things" on the left side foreground and left-center of the picture are supposed to be? They remind me of monsters or goblins or some such I recall seeing in some of the horror comic books when my kids were 10 or so.
Posted: Thu May 22, 2008 5:24 pm
by BMAONE23
They look like Volcanic Glass spires that have melted and drooped in the heat.
Posted: Thu May 22, 2008 10:41 pm
by Arramon
I thought that also, hardened magma slowly eroding by the constant bombardment of the solar particles/wind since its so close. But some do look like creatures with folded wings perching on outcrops. =)
Posted: Thu May 22, 2008 10:58 pm
by iampete
BMAONE23 wrote:They look like Volcanic Glass spires that have melted and drooped in the heat.
Arramon wrote: . . . hardened magma slowly eroding . . .
Doesn't sound unreasonable. Thanks. It was just the weirdness of the shapes that took me aback.
Posted: Fri May 23, 2008 12:28 am
by iamlucky13
BMAONE23 wrote:They look like Volcanic Glass spires that have melted and drooped in the heat.
I'm pretty sure this is the effect the artist was trying to convey. You sometimes can find similar shapes in Hawaii. Solar erosion is very slow, and Gliese 876 is a red dwarf, so it has a relatively weak solar wind.
Posted: Fri May 23, 2008 4:39 pm
by BMAONE23
Arramon wrote:I thought that also, hardened magma slowly eroding by the constant bombardment of the solar particles/wind since its so close. But some do look like creatures with folded wings perching on outcrops. =)
They reminded me of those creatures in Pitch Black
Posted: Fri May 23, 2008 6:51 pm
by Arramon
Good 'b' movie. Much better after part 2 came out. Although this view reminds me of the prison planet in part 2. Crematoria or whatever. =)
