BP's Astronomy Unanswered questions...

QuantumGravity · Post by **QuantumGravity** » Wed Aug 18, 2004 4:39 pm

Hi all,

My school has a few astronomy questions we are wondering about and still have not managed to obtain the answers for them. We've asked quite a few people people including Dr. Phil Chan from NYP. Here are the questions:

1) Why are green stars hotter than blue stars? According to Wien's law, blue stars should have a hotter temperature, but Wolf-Rayet stars, being green are hotter than blue stars. This is a fact.

2) Why can't an Einstein Cross have more than 4 images, not counting the central image?

3) Does the intersection in the analemma have any significance?

I've already asked the second question aleady so it's ok. Any answers to the others?

Thanks

gwenyi · Post by **gwenyi** » Wed Aug 18, 2004 8:13 pm

for the third qns, one end of the analemma is on june 21st and the other is on december 21st. so, the intersection should give u the day which is in between the two listed dates.

http://jrscience.wcp.muohio.edu/photos/WashDC1997.gif

QuantumGravity · Post by **QuantumGravity** » Wed Aug 18, 2004 9:13 pm

Yeah, i understand that. But is there any astronomical happenings in the intersection?

A 5 YeaR Old · Post by **A 5 YeaR Old** » Mon Aug 30, 2004 8:24 pm

yeah, does it coincide with the vernal eqinox (wrong spelling

) or other stuff?
I am from BPGHS too.

shoelevy · Post by **shoelevy** » Mon Aug 30, 2004 8:38 pm

eh...wat's the answer to the 2nd quest?

QuantumGravity · Post by **QuantumGravity** » Mon Aug 30, 2004 8:46 pm

For the 2nd question, some here said that it's got to do with the positioning of the object behind the object which causes the gravitational lensing. Anyway, i'm more interested in the first question... seems really weird...

A 5 YeaR Old · Post by **A 5 YeaR Old** » Mon Aug 30, 2004 9:04 pm

okay, for question 2, if the object behind the object is perfectly aligned with us, we would see a perfect disk round the object at the front.
about the cross, i forgotten bout it already, but i remember that it is used to calculate distances from (forgot) to earth. the light from each point arrives at earth at different times. I remembered a observatory waited for 1 year plus between flickers of 2 points.

shoelevy · Post by **shoelevy** » Mon Aug 30, 2004 9:32 pm

oh
so the 4 dots arrive to us at different times?
i thought we see it simultaneously so i was kinda confused cos i know of the earlier phenomenon

gwenyi · Post by **gwenyi** » Tue Aug 31, 2004 6:45 am

aiya... for gravitational lensing, it's such that the object is placed behind the big giant lens(probably a galaxy) that it causes the light to be bent in our direction. Coincidentally, 4 of those images happen to form when we see them.

It's something the abell cluster where the galaxies have their images copied dozens of times in the same picture.

cheers,
wenyi

NGC 5139 · Post by **NGC 5139** » Thu May 26, 2005 7:26 pm

Dear Quantum Gravity,

Green stars are not hotter than blue stars

. Wolf-Rayet stars are green, but they are in a new class altogether. The original Harvard system of classification by Annie Jump Cannon has been updated to include a new category, thus it is now WOABFGKM (Tonkin, 2002).

Yes, Wolf-Rayet stars have temperatures from about 40 000 K to 80 000 K. Since they are significantly hotter than O stars as well, they are now placed in a new category.

"According to Wien's law, blue stars should have a hotter temperature, but Wolf-Rayet stars, being green are hotter than blue stars. This is a fact. " Yes, it is a fact, but they are not hotter than blue stars because they are green

. It is just that they are in a class of their own

.

Clear skies
Omega

P.S. A good reference is Practical Amateur Spectroscopy, a volume of many articles, edited by Patrick Moore, published in 2002. The author of the article providing the above information is Stephen Tonkin.