[ StenOdenwald/Astronomer - 2 - 11:01:19 ]
RE: [Sandy/NASAChatHost] Hello and welcome to another Space Scientists Online QuestChat with Astronomer Sten Odenwald! Sten will be in the chatroom and ready to take your questions at 11 am, PDT (2 pm, EDT). Be sure to read Sten's NEWLY UPDATED BIO at: http://quest.arc.nasa.gov/sso/team/odenwald.html
Hi Everyone...Im here now...so give me your best questions about space, astronomy and whatever (I don't do Ann Landers stuff though)

[ StenOdenwald/Astronomer - 5 - 11:09:00 ]
RE: [Gaurav] I heard that different astronomical bodies have different radial velocities some have and some have -. then the question that is our universe is expanding or contracting?
Its expanding very definitely. There are no blue shifts measured in any of the distant galaxies studied so far, and the amount of the shift increases with distance which only happens in universes that are expanding.

[ StenOdenwald/Astronomer - 6 - 11:11:44 ]
RE: [Gaurav] when a ray of light passes from the area near the star it bends. It is called as gravitational lensing. Then why it bends once? why it does not go on circulating the star?
Because the gravitational field at the point of closest approach of the light ray is not strong enough. For the sun, the deviation is only 1.75 seconds of arc because it is such an extended body. If the mass were condensed into a 20km radius object like a neutron star, the deflection would be 10 degrees or so, and for a black hole with the same mass but a radius of 2.7 km, it would be 360 degrees and so it would be captured into a 'photon orbit' just outside the black holes event horizon.

[ StenOdenwald/Astronomer - 9 - 11:14:43 ]
RE: [Gaurav] What is actually a dark matter?
We dont know exactly. Currently, from studies of the dark matter halo of our galaxy, the candidates are not white dwarfs or other stellar bodies. This has now been all but ruled out. The only viable candidate now seems to be some type of new particle, a second cousin to the neutrino perhaps. Thats why particle physicists are now developing detectors to find these particles and study them. There could be thousands of them passing through your room every minute.

[ StenOdenwald/Astronomer - 10 - 11:17:00 ]
RE: [Gaurav] So do you believe in Big-Bang? if yes then what was outside the stage when the universe was in singularity? I heard that Andromeda have negetive radial velocity then why the blue shift is measured in this case?
Big Bang is not a 'belief system'. It does seem to be the best idea we have that fits all the data. It will be replaced by a better idea in years to come, just as Einsteins relativity replaced Newtons physics...but we still use Newtonian mechanics just fine. As fo what happened before...we dont even know if that question has a meaning...it is certainly NOT something we can subject to the conventional scientific method!.

[ StenOdenwald/Astronomer - 11 - 11:23:09 ]
RE: [Gaurav] So do you believe in Big-Bang? if yes then what was outside the stage when the universe was in singularity? I heard that Andromeda have negetive radial velocity then why the blue shift is measured in this case?
The Andromeda galaxy is approaching the Milky Way at about 250 km/sec. It has this velocity because it is a member of a cluster of galaxies whose gravitational fields make more of a difference to galaxy dynamics on these small scales, than the expansion of the universe.

[ StenOdenwald/Astronomer - 15 - 11:29:07 ]
RE: [Gaurav] why the centres of the galaxies appear bright? is it due to the stars in that region? why the nucleus of the Syfert galaxies is very bright?
Mostly because of the density of stars being 100-1000 times higher than in the outer regions. Some galaxies, like Seyferts, are 'active' and probably have massive black holes eating stars and gas and producing lots of luminosity.

[ StenOdenwald/Astronomer - 16 - 11:30:41 ]
RE: [Gaurav] what is anomalous redshift? is it diffrent from noral redshift?
Im not sure I know the context of the remark. Halton Arp claims that redshifts are not cosmological and are 'anomalous' for that reason, but he has yet to validate his claim.

[ StenOdenwald/Astronomer - 19 - 11:33:21 ]
RE: [Gaurav] what are brown dwarfs?
These are stars that have masses about 0.05 times the suns mass, which are not planets like jupiter but actually failed stars. They may be fusing deuterium in their cores but they dont have the mass to fuse hydrogen to become stars.

[ StenOdenwald/Astronomer - 22 - 11:35:10 ]
RE: [Gaurav] As there are only gases on the Sun then if we neglet the point of intensity is it possible for us to see through the Sun?
No, unless you use a method other than involving light. FOr instance, SOHO scientists can detect shock waves from surface disturbances on the far side of the sun by using measurements of how the suns surface vibrates.

[ StenOdenwald/Astronomer - 23 - 11:35:43 ]
RE: [Gaurav] Sir, i have read about the Jeans and Jefrie's Tidal wave theory. If we assume it to be true then in your opinion who is the companion star of the Sun.
Sorry...Ive not heard of this before

[ StenOdenwald/Astronomer - 24 - 11:36:31 ]
RE: [Gaurav] a pulsar pulsate. Does it mean that the relative size of that star increases and decreases as it happens in the end of the life of some stars?
Pulsars do not pulsate, they rotate very rapidly and this causes a periodic beamiong of radiation toward earth if the geometry is favorable.

[ StenOdenwald/Astronomer - 26 - 11:38:39 ]
RE: [Gaurav] Sir, I have my friend Nitin sitting with me. He wants to ask you that what are your ideas about ET's
They could be there, but perhaps not in the way that science fiction has trained us to look for them. I think there is lots of bacterial life out there, but interstellar travel is impossible for any number of technological, financial and psychological reasons...let alone the biological ones...so if ET exists, we will not learn about it by other than telescopic means.

[ StenOdenwald/Astronomer - 27 - 11:39:52 ]
RE: [Gaurav] why it is assumed that if we receive a signal from ET's it comes to be in the range of 21cm long amplitude? does this 21cm long line represents Hydrogen and other necessary atoms for life?
Yes..its the strongest radio signal that hydrogen atoms produce. SOme people feel that this is an obvious freqency to start with.

[ Sandy/NASAChatHost - 28 - 11:40:20 ]
Gaurav: You're asking some pretty heavy questions of Astronomer Sten. Good for you! You've really got him thinking today :-) At the end of today's chat, please let us know how we did by filling out the short survey form at: http://quest.arc.nasa.gov/qchats/qchat-surveys

[ StenOdenwald/Astronomer - 30 - 11:41:23 ]
Just in general, did you know that the current count of planets we have detected outside our solar system is now 34?

[ StenOdenwald/Astronomer - 32 - 11:42:51 ]
RE: [Gaurav] Sir,We would like to be in contact with you and wish to ask more questions to you. Can you please provide me your E-mail acount?
I would like to continue answering questions of you, but out of fairness to others I am going to recommend that you come back to this chat room next time and ask them then..OK?

[ StenOdenwald/Astronomer - 34 - 11:44:13 ]
RE: [Gaurav] is the concept of wormholes is true or is it just an idea?
They are predicted by general relativity, but I have no idea how one would prove they exist because from our end most of them look like black holes, and you dont know if they are wormholes unless you actually fall into one.

[ StenOdenwald/Astronomer - 35 - 11:45:03 ]
RE: [Gaurav] Barycentre of the moon and the earth lies inside the earth then why a two stage rocket is required to go to moon?
These are not related issues. You still have to reach earth escape velocity to get to the lunar surface.

[ Sandy/NASAChatHost - 36 - 11:45:30 ]
RE: [StenOdenwald/Astronomer] I would like to continue answering questions of you, but out of fairness to others I am going to recommend that you come back to this chat room next time and ask them then..OK?
Just so you know... Sten's next chat will be Thursday, May 4 at 11 am, PDT (2 pm, EDT). The chat room will be open later today for registration (http://quest.arc.nasa.gov/sso/chats

[ StenOdenwald/Astronomer - 38 - 11:46:32 ]
RE: [Gaurav] yes sir. I know that some planets are discovered and latest 13 floating planets are discovered in the orion.
Thats right...planets everywhere!

[ Sandy/NASAChatHost - 39 - 11:46:50 ]
There are only a few more minutes left in our chat with Sten today. If you have a couple more questions, go ahead and send them now before we have to let Sten get back to his real work!

[ Sandy/NASAChatHost - 40 - 11:48:02 ]
Be sure to fill out the short survey on how we did today, as soon as this chat is over-- http://quest.arc.nasa.gov/qchats/qchat-surveys

[ StenOdenwald/Astronomer - 42 - 11:49:43 ]
RE: [Gaurav] Why a parabolic mirror is used in Newtonian telescope? does it perform some special operation?
yes...starlight entering the telescope are in parallel rays. these have to be focussed to a point to be detected and magnified. The parabolic shape allows parallel rays to be focussed to a single point unlike spherical mirrors.