I need some help please!!! [img]/phpBB/images/smiles/icon_eek.gif[/img] I'm giving a talk for my daughter's 6th grade science class on space. We are going to be building a scale of the Solar System. Since there unit is supposed to be about space travel I wanted to add distances to stars.

What is the closest system that has extra solar planets, and what is the closest single (not part of a multiple star system) Sun like, star. I'm looking for close by candidits to travel to that would support life.

Thank you for your support!


<font size=-1>[ This Message was edited by: hullaballo on 2001-10-30 07:41 ]</font>

I can't give you answers but can suggest you goto your search engine and search on Goeff Marcy, Berkley. Sorry, I didn't bookmark it, or I'd give your the URL. His site is quite informative.

I did a couple of talks to my sons 6th grade class. The first one, I took them to the football field, hung solar system object names on them and we made a human solar system map on a one hundred yard scale. We had great fun. At that scale, Prox. Cent. is about 435 miles away. The kids were staggered by that fact. It really put things in perspective for them.

The second talk, I took my telescope up and we looked a Sun spots until it clouded over. Again, great fun.

I hope I helped.

__________________
It's just one of those damn things of which there are many few. -- Dan Blocker

Two Websites for starters (I did a Google search on "extrasolar planets"):

The Extrasolar Planets Encyclopedia:
http://www.obspm.fr/encycl/encycl.html
provides info on all the extrasolar planets found.

This article: http://physicsweb.org/article/world/14/1/7
indicates that the closest one is around Epsilon Eridani (10.7 ly away).

This is cool, by the way, because according to Star Trek lore E Eridani is the solar system of the planet Vulcan.

Additional links:

Exoplanets - Introduction
http://www.generation.net/~mariob/as...an/intro-e.htm

Terrestrial Planet Finder
http://tpf.jpl.nasa.gov/index.html

Extrasolar Visions - An Extrasolar Planets Guide
http://www.jtwinc.com/Extrasolar/mainframes.html

From the last one, it seems Proxima Centauri may have an extra-solar planet (unless it's a brown dwarf companion).

http://www.geocities.com/atlasoftheuniverse/12lys.html

Tau Ceti (11.9 ly) is the nearest sun-like star.

Remember that not all Extra-Solar planets seem to need a star. I seem to recall a number of the ones found so far were "drifters" without a homestar.

Jeff

Thanks for all the responses. This is 3-4 year I've done this for this teacher, and I try to add a little something each year.

If you want to do this, (it is a real eye openner, for me too) a great web site is;
http://www.exploratorium.edu/ronh/solar_system/

You can create different scales for your model.

A question for those in the know. As long as I have been around occasionally (every couple of years or so) people have said that they have detected the presence of an extrasolar planet by the wobble it causes the star it orbits. Generally when this has happened they have been roundly trashed by every other astronomer soon afterwards. Recently however astronomers seem to have gained the ability to detect extrasolar planets and claim to have found several. What has changed? Do astronomers now have any more evidence than they did before? If so what is it?

Having just finished Ken Croswell's excellent book on the subject ("Planet Quest"), I feel eminently qualified to respond.

First, there seems to have been a lot of wishful thinking in terms of detecting planets: too-quick announcing, optimistic interpretation of results. (Someone allegedly found a planet whose period was -- surprise, surprise! -- exactly the same as that of the earth. It took some investigation to realize that this was a systematic error, though it amazes me that this finding made it to publication at all.)

Second, some of the former debunkers are now among the finders. Geoff Marcy, who may be the world leader in the area, was once notorious for discrediting previous supposed discoveries.

Third, techniques and technology have improved. Rather than astrometry (seeing if the stars change position in the sky), Marcy & co. use Doppler shift detection, which is vastly harder to do but less susceptible to systematic errors. Interferometry is going to be coming into play in the near future, which should lead to a huge increase in planet discoveries.

Hope this helps.

The results are still too marginal to say anything one way or another. Observing Proxima is very difficult, and even the extremely high-resolution Hubble guidance camera data is not good enough to know for sure.

__________________
Phil Plait
The Bad Astronomer
http://www.badastronomy.com
badastro@badastronomy.com

Upon reflection, I wonder how much science really does proceed two steps forward, one step back (like the planet discoveries). It's just more visible in this case because each proposed discovery makes headlines.

Perhaps the BA or some of the other pros here could comment.

[img]/phpBB/images/smiles/icon_confused.gif[/img] BA, could you please expand on this? I'm not sure I follow the reason for the difficulty. Is it because they are looking for an astrometric displacement rather than a doppler shift? [img]/phpBB/images/smiles/icon_confused.gif[/img]

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Ok, here it is, post number 51. Let's make it a good one...

How the heck can you detect an extra-solar planet which doesn't orbit a star? Planets are really small, in the grand scheme of things. And it's not like they have neon signs that say "look! Over here, I'm a planet!"

We can barely find Proxima Centauri, which is a small star, but still a star.

Also, if it's just wandering through the universe, why is it a planet and not just space junk. Which brings us again to the definition of planet, viz Pluto. I seem to recall that none of the definitions of planet which were offered up would classify a big old chunk of rock moseying through our corner of the galaxy as a planet.

Which brings us to the Death Star and small moons (Star Wars, taking over the world again). If it's not orbiting something, why would it be a moon? Likewise, if it's not grinding around a star, why would it be a planet?

Ok, that's enough. I love the repeated question... Ahh...

Ben

[img]/phpBB/images/smiles/icon_biggrin.gif[/img]

The Fine Guidance Sensors can give you extremely sensitive astrometry (position measurements) of a star. They were used repeatedly to look for a wobble in the motion of Proxima as it moves across the sky, and none was found. Oddly, I cannot seem to find any reference about this on the web, which makes me wonder if I am mis-remembering it (I know the Faint Object Spectrograph on Hubble was used and found interesting but not conclusive results). If/when I find more I'll post again.

__________________
Phil Plait
The Bad Astronomer
http://www.badastronomy.com
badastro@badastronomy.com

Well, this is my 51st post, so I'll try to give you a good answer. [img]/phpBB/images/smiles/icon_smile.gif[/img]

Recently, several objects were detected by microlensing during observation of a globular cluster. I don't know how they determined it exactly, but these objects seem to be very small. Less massive than brown dwarfs for example.

Of course, microlensing is a non-repeatable observation, so it would be almost impossible to confirm any individual observation, but with so many events detected here, chances are good that we will be able to observe more of them.

Here's a link to it.

http://origins.jpl.nasa.gov/library/.../062701-a.html

__________________
...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

I found it: http://adsabs.harvard.edu/cgi-bin/np...8e0b7728728595 for those interested.

Okay. Says should be confirmed or refuted by fall of '94. It is now fall of '01. [img]/phpBB/images/smiles/icon_confused.gif[/img] Was it?

__________________
Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson

Ben, David

Shooting star fireworks for y'all

Whoo! A galaxy-sized roman candle. I want one of those. [img]/phpBB/images/smiles/icon_biggrin.gif[/img] Thanks!

Hmm, wonder what it would look like on a planet near (but not TOO near [img]/phpBB/images/smiles/icon_smile.gif[/img]) something like that. Let's say about 50,000ly off to one side. It does say it's visible in optical wavelengths, but I wonder if it would it be visible to the naked eye from that distance or if it would it be too diffuse?

__________________
...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

Heat. Free-range planets, especially those approaching brown-dwarf size, might put out enough of a thermal signature to be detectable against the cold background of space. Though they would have to be awfully close to be indistinguishable from simple data errors in any image from an infra-red telescope.

Guessing:
Size and shape.
There are probably min and max size limits (too big to be oort cloud debris, too small to start fusion at its core).

Size and shape expectations. Conventionally, we visualize moons as spherical but asteroids as freshly dug potatoes. There are notable exceptions of course. From a distance, the Death Star appeared spherical with one heckuvva impact crater on the northern hemisphere AND it was found not far from Alderran (or its remains), so Luke might be forgiven for assuming it was a small moon of that planet.

Of course, whether a free floating body could be considered a planet depends on what definition of "planet" you are using. I think I can feel safe to say that most of the people here would not technically think of such a body as a planet, per the recent discussions we've had about it.

But, on another level, a more casual one, I don't think it's a crime to call such an object a planet. If it's roughly planet-sized and either rocky or gaseous then it could be called a planet as a sort of shorthand. I suppose such objects would more properly be termed "planetoids" or "free-floating planetary objects" or some such jargonese. But as long as we know what we're talking about we can use whatever is generally understood.

And of course this could also apply to moons, a-la the Star Wars thing. [img