http://apod.nasa.gov/apod/ap090131.html
You are my lucky star
I saw you from afar
Two lovely eyes at me
![Image](http://www.toughpigs.com/images/recastlink.jpg)
They where gleaming
Beaming
I was starstruck
http://au.youtube.com/watch?v=cFvZtROeJrE
It's a diffuse nebula, not a planetary. It is cataloged as LBN 826, or Sharpless 2-242.Tara_Li wrote:In the full-sized image, there's an object located at about 8 o'clock to the main image showing an extent. I'm curious as to what it is (obviously, it's probably a planetary nebula), and I'm used to stars in Hubble images showing some coloration - so I'm wondering why the stars in this one don't, and why that planetary nebula doesn't show at least some colors. Is this composited with one of the earth-based star surveys?
Not quite sure what you're asking. Presumably, the entire remnant contains a tenuous mix of gases. Shocked regions are heated up enough to ionize these gases and produce light. So in the image, only the hot (shocked) regions are visible. The brightness in each of the color bands must tell something about the temperature and concentration for each of the three elements targeted.astrolabe wrote:Does this mean that the hydrogen, sulfur, and oxygen emissions are they themselves the shocked, glowing gas?
Is that any way to talk about our beloved Link Hogthrob?aristarchusinexile wrote:Remarkably similar to computer simulations of void bubble expansion.
I don't know. It's a complicated question. Intensity is all we have to work with in the image, and that is determined by two variables, density and temperature. Somebody studying this area closely could use spectroscopy to look at the widths of the emission lines, which (due to Doppler broadening) could be used to deduce the temperatures in different areas.astrolabe wrote:A temperature gradient possibly related to light intensity would be an advantagious correlation indeed I would assume. Also areas of the different emissions (with allowances for overlap) seem to be pretty well defined- could this indicate temperature differences as well if each element emits only at certain temperatures- not soley dependent on the heat of the shocked ionized gasses? in other words, is there any indications that the hydrogen, sulfur, and oxygen are homogenous throughout the nebula or are we limited to only the areas of emission as the element locators?
It is generally customary to ignore distance. Under the conventions of special relativity, an event "happens" when it is observed. So it is perfectly correct to say that the SN happened 40,000 years ago, regardless of how far away it actually is. I took the sentence as an explanation of that definition of an event's occurrence time.Zigomer Trubahin wrote:Just one observation, the text says "This supernova remnant has an estimated age of about 40,000 years - meaning light from the massive stellar explosion first reached Earth 40,000 years ago." I don't see the logical correlation between the two parts of the sentence. Light from a thing the age of about 40,000 years can reach the Earth any time (any time later than 40,000 years ago), depending on the distance. It could reach us today, or tomorrow. As this cloud is 3,000 ly away, the time its light first reached the Earth should have been about 37,000 years ago. Not that it matters much.:)
Thank you for sticking with me on this and for your astute appraisal of my question. I'm glad I persisted for it resulted in a very abundant and informative answer that I can understand. Good thought order too!Chris Peterson wrote: I don't know. It's a complicated question. Intensity is all we have to work with in the image, and that is determined by two variables, density and temperature. Somebody studying this area closely could use spectroscopy to look at the widths of the emission lines, which (due to Doppler broadening) could be used to deduce the temperatures in different areas.
Also, the ionization energies are different for the three elements, so just because an area looks like a single color, that doesn't necessarily mean it consists of only the one element. And there's some continuum energy diluting things as well.
Finally, I suspect the elements are not homogeneous at all. When a star explodes, it has an internal shell structure consisting of different elemental zones. You'd think some of that structure would be preserved in the remnant- although it might be so chaotic that you couldn't work backwards to learn anything about the progenitor.
The important thing is not so much when a prehistoric supernova "happens"Chris Peterson wrote:It is generally customary to ignore distance. Under the conventions of special relativity, an event "happens" when it is observed. So it is perfectly correct to say that the SN happened 40,000 years ago, regardless of how far away it actually is. I took the sentence as an explanation of that definition of an event's occurrence time.Zigomer Trubahin wrote:Just one observation, the text says "This supernova remnant has an estimated age of about 40,000 years - meaning light from the massive stellar explosion first reached Earth 40,000 years ago." I don't see the logical correlation between the two parts of the sentence. Light from a thing the age of about 40,000 years can reach the Earth any time (any time later than 40,000 years ago), depending on the distance. It could reach us today, or tomorrow. As this cloud is 3,000 ly away, the time its light first reached the Earth should have been about 37,000 years ago. Not that it matters much.
Simeis 147 is the Benjamin Button of supernova remnants![b] http://antwrp.gsfc.nasa.gov/apod/ap051129.html [/b] wrote: Explanation: It's easy to get lost following the intricate filaments in this detailed image of faint supernova remnant Simeis 147. Seen towards the constellation Taurus it covers nearly 3 degrees (6 full moons) on the sky corresponding to a width of 150 light-years at the stellar debris cloud's estimated distance of 3,000 light-years. The above image is a color composite of 66 blue and red color band images from the National Geographic Palomar Observatory Sky Survey taken with the wide field Samuel Oschin 48-inch Telescope. The area of the sky shown covers over 70 times the area of the full Moon. This supernova remnant has an apparent age of about 100,000 years - meaning light from the massive stellar explosion first reached Earth 100,000 years ago - but this expanding remnant is not the only aftermath. The cosmic catastrophe also left behind a spinning neutron star or pulsar, all that remains of the original star's core.
Benjamin Button: Some people, were born to sit by a river. Some get struck by lightning. Some have an ear for music. Some are artists. Some swim. Some know buttons. Some know Shakespeare. Some are mothers. And some people, dance.
Is there a difference? It "happened" 40,000 years ago, because that's when it was observed from Earth. Which also means it's 40,000 years old. The bottom line is that it isn't particularly useful to estimate when it "really" happened based on its distance (although that may be a fun thing to do).neufer wrote:The important thing is not so much when a prehistoric supernova "happens"Chris Peterson wrote:It is generally customary to ignore distance. Under the conventions of special relativity, an event "happens" when it is observed. So it is perfectly correct to say that the SN happened 40,000 years ago, regardless of how far away it actually is. I took the sentence as an explanation of that definition of an event's occurrence time.
but rather how old the SNR is that we observe now.
The Simeis 147 SNR that we observe now is apparently about 40,000 years old.
Who exactly observed it from Earth? ...Or as the old saying goes:Chris Peterson wrote:Is there a difference? It "happened" 40,000 years ago, because that's when it was observed from Earth.neufer wrote:The important thing is not so much when a prehistoric supernova "happens"Chris Peterson wrote:It is generally customary to ignore distance. Under the conventions of special relativity, an event "happens" when it is observed. So it is perfectly correct to say that the SN happened 40,000 years ago, regardless of how far away it actually is. I took the sentence as an explanation of that definition of an event's occurrence time.
but rather how old the SNR is that we observe now.
The Simeis 147 SNR that we observe now is apparently about 40,000 years old.
So you agree that it "really" happened 40,000 years + distance in light years ago.Chris Peterson wrote: Which also means it's 40,000 years old. The bottom line is that it isn't particularly useful to estimate when it "really" happened based on its distance (although that may be a fun thing to do).
I put "really" in quotes to reflect the very difficult to define meaning of the word. I certainly think that there's a valid frame of reference that sets one meaning of "really happened" to mean the time it was observed here plus the light time for the signal to get here. But as I said, that usage isn't generally very useful, which is why you don't usually see it used except in explanations for a lay audience. Nothing wrong with that, of course.neufer wrote:So you agree that it "really" happened 40,000 years + distance in light years ago.Chris Peterson wrote: Which also means it's 40,000 years old. The bottom line is that it isn't particularly useful to estimate when it "really" happened based on its distance (although that may be a fun thing to do).
So, by that definition, I guess:Chris Peterson wrote:I put "really" in quotes to reflect the very difficult to define meaning of the word. I certainly think that there's a valid frame of reference that sets one meaning of "really happened" to mean the time it was observed here plus the light time for the signal to get here. But as I said, that usage isn't generally very useful, which is why you don't usually see it used except in explanations for a lay audience. Nothing wrong with that, of course.neufer wrote:So you agree that it "really" happened 40,000 years + distance in light years ago.Chris Peterson wrote: Which also means it's 40,000 years old. The bottom line is that it isn't particularly useful to estimate when it "really" happened based on its distance (although that may be a fun thing to do).
I'm not following your reasoning here. If you're trying to place all these events into a common time reference, don't you need to include the distances for the latter two?neufer wrote:So, by that definition, I guess:Chris Peterson wrote:I certainly think that there's a valid frame of reference that sets one meaning of "really happened" to mean the time it was observed here plus the light time for the signal to get here.
Tycho's Supernova at ~8,000 years [= 436 years + 7,500 (light-)years] was the last known supernova to occur.
Kepler's supernova at 404 years is "the most recent stellar explosion seen to occur within our Milky Way galaxy."
And Supernova remnant G1.9+0.3 at ~140 years is the youngest known supernova remnant (SNR) in the Milky Way Galaxy.
Sorry, I was NOT trying to place all these events into a common time reference.Chris Peterson wrote:I'm not following your reasoning here. If you're trying to place all these events into a common time reference, don't you need to include the distances for the latter two?neufer wrote:So, by that definition, I guess:Chris Peterson wrote:I certainly think that there's a valid frame of reference that sets one meaning of "really happened" to mean the time it was observed here plus the light time for the signal to get here.
Tycho's Supernova at ~8,000 years [= 436 years + 7,500 (light-)years] was the last known supernova to occur.
Kepler's supernova at 404 years is "the most recent stellar explosion seen to occur within our Milky Way galaxy."
And Supernova remnant G1.9+0.3 at ~140 years is the youngest known supernova remnant (SNR) in the Milky Way Galaxy.
<<The scientists discovered the pulsar, named PSR J1748-2446ad, in a globular cluster of stars called TERZAN 5, located some 28,000 light-years from Earth in the constellation Sagittarius. The newly-discovered pulsar is spinning 716 times per second, or at 716 Hertz (Hz), readily beating the previous record of 642 Hz from a pulsar discovered in 1982. The scientists say the object's fast rotation speed means that it cannot be any larger than about 20 miles across. According to Hessels, "If it were any larger, material from the surface would be flung into orbit around the star." The scientists' calculation assumed that the neutron star contains less than two times the mass of the Sun, an assumption that is consistent with the masses of all known neutron stars.>>
How about SN 185, at ~4800 years (1823 years ago + 3000 ly distant)?neufer wrote:I now think that SN 1054 (M1: The Crab Nebula) at ~7,000 years ago [= 954 years + 6,000 (light-)years] was the last known supernova to occur.
Heliocracy wrote:What's that puffy, cloud-like object that appears near the lower left corner of the Simeis 147 photo?
Tara_Li wrote:In the full-sized image, there's an object located at about 8 o'clock to the main image showing an extent. I'm curious as to what it is (obviously, it's probably a planetary nebula), and I'm used to stars in Hubble images showing some coloration - so I'm wondering why the stars in this one don't, and why that planetary nebula doesn't show at least some colors. Is this composited with one of the earth-based star surveys?
http://asterisk.apod.com/vie ... 82#p100711Chris Peterson wrote:It's a diffuse nebula, not a planetary. It is cataloged as LBN 826, or Sharpless 2-242.