view of the Sun (APOD 21 May 2008)

[Mac Coak]

Would our Sun look that big if viewed from Mercury? Mac

[henk21cm]

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.

[apodman]

APOD description mentions "gravitational tides".

Is there another kind?

[Arramon]

This picture is so awesome... helluva job done by the artist. =)

*background image set*

[astrolabe]

Hello apodman,

Yes, there are centrifugal tides.

[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.

[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.

[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.

[BMAONE23]

They look like Volcanic Glass spires that have melted and drooped in the heat.

[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. =)

[iampete]

They look like Volcanic Glass spires that have melted and drooped in the heat.

. . . hardened magma slowly eroding . . .

Doesn't sound unreasonable. Thanks. It was just the weirdness of the shapes that took me aback.

[iamlucky13]

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.

[BMAONE23]

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

[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. =)