PDA

View Full Version : Antares is that big?

Nonkers
2006-Jun-22, 04:19 PM
The crippler in these pictures is the difference in size between the Sun and Antares! http://www.rense.com/general72/size.htm

How do we know that Antares is really that big?

HenrikOlsen
2006-Jun-22, 04:28 PM
Great series of pictures, though I temporarily got confused about the purpose because pics 2 and 3 are swapped.

ngc3314
2006-Jun-22, 04:33 PM
The crippler in these pictures is the difference in size between the Sun and Antares! http://www.rense.com/general72/size.htm

How do we know that Antares is really that big?

Several ways. Given that we can estimate the star's distance via parallex or comparison with others stars of nearly identical temperature and surface gravity (known from their spectra),

(1) Antares is in the band of sky which occcasionally gets occulted by the Moon, and we can measure the size of stars in such events by how long it takes for the starlight to vanish. (In real life this is complicated by diffraction of light at the Moon's edge, but Antares is quite large and it doesn't change the answer all that much).

(2) Interferometry, combining light from separated telescopes. Small stars have light so nearly parallel from all parts of the star that it interferes constructively until the telescopes are widely separated, but large stars start to have destructive interference for closer pairs of telescopes from opposite sides of the star. This lets people measure not only the size of stars, but their degree of fading to the edge (limb darkening).

(3) A rough-and-ready approximation comes from the fact that stars' surface layers approximately fulfill the conditions for blackbody radiation (a hot opaque object). This means that to the same level of approximation, the energy released per unit surface area of the stars is constant*T^4. Th constant involves lab physics, and T can be measured closely from the spectrum. Then we can solve for the surface area, and thus radius, by asking how large the star at that temperature has to be for it to be the observed brightness at that distance.

There are a handful of stars (Betelgeuse, maybe R Doradus) for which the Hubble telescope can barely image the disk size (especially in the UV where its resolution is best).

Maksutov
2006-Jun-22, 04:35 PM
How do we know that Antares is really that big?There are many ways to measure the size of stars. Here's one way (http://planetquest.jpl.nasa.gov/SIM/experiment_2.cfm) that you can even try at home, with the proper equipment.

antoniseb
2006-Jun-22, 04:38 PM
There are several things necessary for coming to this conclusion. We need to determine the distance and calculate either the surface area (based on brightness and color which implies luminosity for each square meter) or determine the angular diameter (based on either on direct measurement from an image, or by the implied diameter from a interference fringes).

In the case of Antares, we have all three.

Doodler
2006-Jun-24, 05:52 PM
When that thing pops, its going to be absolutely spectacular.

parallaxicality
2006-Jun-24, 06:05 PM
What will happen to Antares B when Antares blows?

Will we have any advance warning before it does?

Maksutov
2006-Jun-24, 06:17 PM
Will we have any advance warning before it does?Yes, but such things haven't shown up yet. Information on this star may be found here (http://chandra.harvard.edu/resources/faq/sources/stars/stars-28.html)and here. (http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970221b.html)

George
2006-Jun-24, 06:53 PM
The crippler in these pictures is the difference in size between the Sun and Antares! http://www.rense.com/general72/size.htm

How do we know that Antares is really that big?

Just a nit...the size depiction in the link, comparing Antares and Betelgeuse, does appear to be in error. Betelgeuse is only less than 10% smaller in diameter than Antares (650 solar dia. vs. 700 solar dia., respectively). I could be wrong, however, because Betelgeuse and Antares are variable stars. Betelgeuse can vary from 550 to 920 solar diameters.

If you like size, consider their chromospheres, they extend the diameter nearly to Pluto!

Since we are on the subject of Antares (I really must ask).... what color is this "red" supergiant?

[Added: overexposure on red stars tend to look yellow, so I withdraw my color question. If anyone has a red Antares, please share it.]

Kaptain K
2006-Jun-26, 08:18 AM
Another nit... In the first image, the Earth and Venus are so close in size that on the scale of those models, they would be so close in size that they would appear identical.

Maksutov
2006-Jun-26, 08:24 AM
Just a nit...the size depiction in the link, comparing Antares and Betelgeuse, does appear to be in error. Betelgeuse is only less than 10% smaller in diameter than Antares (650 solar dia. vs. 700 solar dia., respectively). I could be wrong, however, because Betelgeuse and Antares are variable stars. Betelgeuse can vary from 550 to 920 solar diameters.

If you like size, consider their chromospheres, they extend the diameter nearly to Pluto!

Since we are on the subject of Antares (I really must ask).... what color is this "red" supergiant?

[Added: overexposure on red stars tend to look yellow, so I withdraw my color question. If anyone has a red Antares, please share it.]I've been looking at Antares since 1960, and the alpha star in my favorite constellation has alway looked red to me.

George
2006-Jun-26, 12:54 PM
I've been looking at Antares since 1960, and the alpha star in my favorite constellation has alway looked red to me.
It should look red, but I recently imaged it from Kitt Peak and got yellow. After checking other sites for images, they show yellow, too. I got worried because it shouldn't look yellow; Antares' peak is at 855nm (IR), with much more red and orange than the other colors. :shifty: But I realized that my image and the others were likely just overexposed which causes the red to look yellow (hence the addition to the post).

It would be nice to see a red image of a "red" supergiant. Got any?

parallaxicality
2006-Jun-26, 03:20 PM
Antares's name comes from "Anti-Ares", ie, "Against Mars" because it's red and in the ecliptic.

Click Ticker
2006-Jun-26, 03:44 PM
My question would be:

Using the 3rd picture, how wide would your computer monitor have to be to put the planets at their proper orbital distance from the sun?

I'm guessing better than 100 kilometers wide - but that's just a SWAG.

Doodler
2006-Jun-26, 04:11 PM
My question would be:

Using the 3rd picture, how wide would your computer monitor have to be to put the planets at their proper orbital distance from the sun?

I'm guessing better than 100 kilometers wide - but that's just a SWAG.

Depends on how big the models actually are.

George
2006-Jun-26, 04:26 PM
Antares's name comes from "Anti-Ares", ie, "Against Mars" because it's red and in the ecliptic.
But if it is against Mars, shouldn't it be blue? ;)

Kaptain K
2006-Jun-26, 04:53 PM
"Rival of Mars" would be a better translation!

Click Ticker
2006-Jun-26, 05:04 PM
Depends on how big the models actually are.

That much I realize. I was referring to the size that they appear in the picture. Shouldn't that be about the same to all of us regardless of the monitor we're using?

Click Ticker
2006-Jun-26, 05:09 PM
Looks like I overestimated a tad. I measured 2.8 inches.

http://www.exploratorium.edu/ronh/solar_system/

This gave me about 1,000 ft to Pluto.

George
2006-Jun-26, 06:13 PM
"Rival of Mars" would be a better translation!
Ah yes...rendering it a really red rivalry; therefore, I must recant. :razz: [Mars is kinda orange, though.... oh well, nevermind :)]

George
2006-Jun-26, 06:16 PM
Looks like I overestimated a tad. I measured 2.8 inches.

http://www.exploratorium.edu/ronh/solar_system/

This gave me about 1,000 ft to Pluto.
Perhaps we should wait till after September. [It'll be much easier if they dump Pluto as a planet. ;)]

HenrikOlsen
2006-Jun-26, 07:29 PM
Antares's name comes from "Anti-Ares", ie, "Against Mars" because it's red and in the ecliptic.

But if it is against Mars, shouldn't it be blue? ;)
Remember that both against and ante- can both mean opposed and near, I'm guessing it's the second meaning that's used in this case.

George
2006-Jun-26, 07:37 PM
Remember that both against and ante- can both mean opposed and near, I'm guessing it's the second meaning that's used in this case.
Yes, I understand. Forgive me when I plug cracks with wise cracks. :)

HenrikOlsen
2006-Jun-26, 07:40 PM
Another nit... In the first image, the Earth and Venus are so close in size that on the scale of those models, they would be so close in size that they would appear identical.
If you measure the diameters on the screen, the difference is indeed the ~5% you'd expect.
Venus looks smaller than that because it's positioned closer, so both lower and upper parts in the picture are lower than their earth counterparts, but the lowest point of the earth is hidden.
It might also be from an unconcoius effect of seeing them as spheres and judging relative masses, ie. 1.053~=1.15 so the earth seems 15% bigger instead of 5%.

tofu
2006-Jun-26, 10:10 PM
Yes, but such things haven't shown up yet. Information on this star may be found here (http://chandra.harvard.edu/resources/faq/sources/stars/stars-28.html)and here. (http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970221b.html)

Your second link there was hilarious. "Hi, I just named my business after this star, can you please give me some information on it."

I wonder if there's someone out there about to name their daycare business after Oedipus, and then later on think to look up that name.

publiusr
2006-Jun-29, 09:23 PM
The crippler in these pictures is the difference in size between the Sun and Antares! http://www.rense.com/general72/size.htm

How do we know that Antares is really that big?

Woof--what a monster.

Pistol Star is bigger though, IIRC

http://antwrp.gsfc.nasa.gov/apod/ap971008.html
http://www.solstation.com/x-objects/pistol.htm

Kaptain K
2006-Jul-09, 05:37 AM
Pistol Star is more massive, but Antares is much larger in diameter.

Dave Mitsky
2006-Jul-09, 07:05 AM
Edit

There are a handful of stars (Betelgeuse, maybe R Doradus) for which the Hubble telescope can barely image the disk size (especially in the UV where its resolution is best).

Mira is another.

http://antwrp.gsfc.nasa.gov/apod/ap981011.html

Dave Mitsky

Maksutov
2006-Jul-09, 09:41 AM
Mira is another.

http://antwrp.gsfc.nasa.gov/apod/ap981011.html

Dave MitskyMIRAbile dictu!

publiusr
2006-Jul-14, 07:36 PM
Nice!

hhEb09'1
2006-Aug-05, 07:19 PM