Search found 17623 matches
- Thu Aug 21, 2008 5:38 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Earth's Shadow (APOD 20 Aug 2008)
- Replies: 65
- Views: 17545
The terminator in this eclipse sense is the edge peak right? I think so. It's the line between night and day on the Earth. If you were standing there, with the setting (or rising) Sun at your back and the partially eclipsed Moon in front of you, your shadow would be cast on the Moon. So everything ...
- Thu Aug 21, 2008 4:59 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Earth's Shadow (APOD 20 Aug 2008)
- Replies: 65
- Views: 17545
So are you telling me there's no hope of making bunny ears appear in our moon shadow? Not even with two gigantic space elevator docking/transfer stations? Even a real bunny standing on the Earth's terminator casts its shadow on the Moon. In the case of a space elevator, the cables would cast shadow...
- Thu Aug 21, 2008 2:23 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Earth's Shadow (APOD 20 Aug 2008)
- Replies: 65
- Views: 17545
I was curious after neufer's post as to how long people believed the earth was flat and was amazed there is a Flat Earth Society in these times. In fact, it's doubtful that many people (at least, people with any hint of education) in the West believed that the Earth was flat after the Greeks demons...
- Tue Aug 19, 2008 3:02 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Witch's Broom Nebula (APOD 19 Aug 2008)
- Replies: 11
- Views: 4234
Re: The Witch's Broom (APOD 2008 August 19)
The wispy cloud is very intricate and colorful; I can see why it is called the veil nebula. Without reading the explanation about the sweeping action on nearby gas; It would be hard to imagine the broom name. Most of the names we have for objects like this stem from their visual appearance in the e...
- Mon Aug 18, 2008 12:14 am
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Io's Surface Under Construction lake-like feature? (17Aug08)
- Replies: 15
- Views: 4339
Re: Io's Surface: Under Construction
Aurora Versus Power Lines Article #506 by T. Neil Davis http://www.gi.alaska.edu/ScienceForum/ASF5/506.html Yeah, these currents are plenty large enough to cause problems. I live in ranching country, and know of anecdotal stories about people getting shocked off of fence lines during active solar p...
- Sun Aug 17, 2008 11:16 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Io's Surface Under Construction lake-like feature? (17Aug08)
- Replies: 15
- Views: 4339
If the surface is constantly changing due to volcanic activity and the throwing up of lava. Does this mean that the moon is getting larger in circumference and more hollow under the surface? A body as massive as Io can't contain much hollow space, as gravity will cause it to collapse. Because this ...
- Sun Aug 17, 2008 11:13 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Io's Surface Under Construction lake-like feature? (17Aug08)
- Replies: 15
- Views: 4339
Re: Io's Surface: Under Construction
I would say that the 1 million ampere electric current flowing between Jupiter and Io would be a much more likely suspect for Io's condition of surface agitation... A more recent article also attributes a wattage of approximately 2 terawatts (2 trillion watts) to the exchange. That's a trivial amou...
- Sun Aug 17, 2008 5:32 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Io's Surface Under Construction lake-like feature? (17Aug08)
- Replies: 15
- Views: 4339
Re: Io (8.17 APOD)
If the picture is of the side of Io that always faces away from Jupiter, and we are looking straight at it, why then does not Jupiter fill the void behind Io? The image was constructed mathematically, by taking many small field-of-view images, at different angles and resolutions, and mapping them o...
- Sun Aug 17, 2008 4:00 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: NGC 6888 Crescent (Medusa?) Nebula (APOD 13 Aug 2008)
- Replies: 15
- Views: 6053
Re: NGC 6888: The Crescent Nebula - APOD 13 Aug 2008
Browsing the handbook of chemistry and physics i foud that iron oxyde melts at about 1500 C, silicium oxyde at about 1700 C. So there is not much difference between the two melting points. The density of iron oxide is about 5500 kg/m³, the density of silicium oxide is 2200 kg/m³. Iron oxide will si...
- Sat Aug 16, 2008 2:24 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: NGC 6888 Crescent (Medusa?) Nebula (APOD 13 Aug 2008)
- Replies: 15
- Views: 6053
Re: NGC 6888: The Crescent Nebula - APOD 13 Aug 2008
The ρ of iron is nearly 8000 kg/m³, the ρ of silicon is nearly 2500 kg/m³. Since a lot of time has gone since the earth was liquid, there was an ample amount of time for iron to sink to the center of the earth, whereas silicon would rise to the outer range of the earth. As a result iron would be a ...
- Fri Aug 15, 2008 10:49 pm
- Forum: The Asterisk Café: Discuss Anything Astronomy Related
- Topic: Comet 109P/Swift-Tuttle Meteor showers
- Replies: 6
- Views: 2182
- Thu Aug 14, 2008 4:47 am
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: NGC 6888 Crescent (Medusa?) Nebula (APOD 13 Aug 2008)
- Replies: 15
- Views: 6053
Re: NGC 6888: The Crescent Nebula - APOD 13 Aug 2008
Nevertheless your thoughts triggered a philosophical question. On earth, the moon, Venus, Mercury, Mars and the moons of the gas giants Silicon seems to the the abundant element. Si is one of the elements in the nuclear fusion chain of stars. Fe (Iron) is the last one. So there must be somewhat mor...
- Fri Aug 08, 2008 1:29 am
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Milky Way Over Ontario (APOD 29 Jul 2008)
- Replies: 23
- Views: 6123
Re: what about natural viewing?
Going to a higher elevation, such as a mountaintop, far from the light pollution also helps. I did that a few times and noticed that I could see more stars than I could in the lowland. Very true. I live at over 9000 feet elevation, and the skies here are somewhat darker than the models estimate. Th...
- Thu Aug 07, 2008 9:02 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Milky Way Over Ontario (APOD 29 Jul 2008)
- Replies: 23
- Views: 6123
Re: what about natural viewing?
Are there places you can go to see deep details without light-gathering? How far out from the city do you have to go? What locales or countries (that are safe) are good for star-gazing, in case I'm ever on vacation somewhere cool? My basic answer would be no. That's not to say you can't go to a goo...
- Thu Aug 07, 2008 5:41 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Total eclipse, so why dawn glow? (APOD 05 Aug 2008)
- Replies: 18
- Views: 6010
The shadow of the Moon in the sky above - was that what you mean, Chris? The shadow cast by the moon is a cone that points away from the Sun, and comes to its vertex at about the same distance as the Earth is from the Moon. A solar eclipse happens when that vertex intersects the Earth. So there is ...
- Thu Aug 07, 2008 2:23 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Total eclipse, so why dawn glow? (APOD 05 Aug 2008)
- Replies: 18
- Views: 6010
That picture certainly shows two 'false sunsets', but surely the dark, truncated cone shape, from 6 to 8 o'clock, is the wing of the aircraft from which the photo was taken? Yes, the shadow at the bottom is the plane's wing. The eclipse shadow is the inverted cone that covers the sky at the top, an...
- Thu Aug 07, 2008 2:21 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Pleiades Star Cluster (APOD 20 Jun 1995)
- Replies: 22
- Views: 5741
- Wed Aug 06, 2008 6:44 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Total eclipse, so why dawn glow? (APOD 05 Aug 2008)
- Replies: 18
- Views: 6010
- Tue Aug 05, 2008 10:02 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: Total eclipse, so why dawn glow? (APOD 05 Aug 2008)
- Replies: 18
- Views: 6010
Re: Total eclipse, so why dawn glow?
There are three kinds of dawn... Your analysis is fine, but the actual situation is much simpler. There's no requirement that we be viewing perpendicular to the path of the eclipse. In fact, the image is taken to the west, and the path was northwest to southeast. Near the end of totality, the shado...
- Mon Aug 04, 2008 12:34 am
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Milky Way Over Ontario (APOD 29 Jul 2008)
- Replies: 23
- Views: 6123
Re: Which camera?
So there are four contrinutions: S: the wanted signal D: the dark current noise R: the readout noise T: the thermal noise. D and T are the same thing. The dark current shows as a steady increase in charge, related to temperature. This can be subtracted from the image, which is the main purpose of a...
- Sun Aug 03, 2008 9:42 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Milky Way Over Ontario (APOD 29 Jul 2008)
- Replies: 23
- Views: 6123
Re: Which camera?
It was late seventies, or early eighties that one of my educators told me about CCD's. In these days it was 'capacitors', that is why i brought in the notion of capacitors. It's true that the pixel structure contains something like a capacitor for storing the initial charge. In most cases, this is ...
- Sat Aug 02, 2008 10:24 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Milky Way Over Ontario (APOD 29 Jul 2008)
- Replies: 23
- Views: 6123
Re: Which camera?
A CCD is a charge coupled device. Incident photons rip off electrons and as a result one plate of the capacitor get a tiny electric charge. Since the capacitor is etched on a semiconductor surface, it is not an ideal capacitor: it leaks... Some CMOS detectors store charge on capacitors. CCDs do not...
- Sat Aug 02, 2008 7:38 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Milky Way Over Ontario (APOD 29 Jul 2008)
- Replies: 23
- Views: 6123
Re: Which camera?
AFAIK, one could average the frames (mainly noise reduction in e.g. planetary photography), one could add up the energy values (to get a 'deeper' image of combined exposure time, for faint objects e.g. nebula) or a combination of both. In practice, there is seldom a difference between the two, unle...
- Sat Aug 02, 2008 7:34 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Milky Way Over Ontario (APOD 29 Jul 2008)
- Replies: 23
- Views: 6123
Re: Which camera?
You triggered another question: stacking of frames. As far as i understand stacking of frames reduces noise whereas the features in the subject are enhanced: noise increases with the square root of the number of frames, the subject increases with the number of frames. Popular software like Registax...
- Fri Aug 01, 2008 2:27 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: The Pleiades Star Cluster (APOD 20 Jun 1995)
- Replies: 22
- Views: 5741
Are you willing to read further and learn about the so called theoretical black holes and jets. Or I'm just wasting my time. I consider myself well educated with respect to current theory on black holes and jet formation. I'm not particularly interested in hearing about theories that haven't been a...