Starship Asterisk*

I've never seen a comet that changed its appearance so quickly. The solar wind and radiation is really tearing at it. These are from this morning and from yesterday morning, so just 24 hours of evolution. Images are 2 degrees wide. _ C_2023P1_20230908.jpg C_2023P1_20230909.jpg Nice images. I'm curi...

I've never seen a comet that changed its appearance so quickly. The solar wind and radiation is really tearing at it. These are from this morning and from yesterday morning, so just 24 hours of evolution. Images are 2 degrees wide. _ C_2023P1_20230908.jpg C_2023P1_20230909.jpg Nice images. I'm curi...

Then I still don't get what you meant by "in a medium they [photons] undergo scattering ( a photon is absorbed and a new one emitted ) which takes time... hence, the light propagates at less than c". How are photons being absorbed/emitted if not via electrons? By quantum mechanisms, where...

Good question. DSS2 was produced between 1996 and 2006. That means there should be 17-27 years between the two pictures... Based on GAIA pm data for this star, I calculate the time difference to be ~23 years. • There is a large proper motion in declination. Proper motion in RA and Dec = 5.6 mas/yr ...

Based on GAIA pm data for this star, I calculate the time difference to be ~23 years. • There is a large proper motion in declination. Proper motion in RA and Dec = 5.6 mas/yr and 101 mas/yr respectively, or a total pm ≈ 102 mas/yr • The angular change ≈ 2.3 arcseconds → 2.3 arcseconds ÷ 0.1 arcsec...

Congratulation to Lorand Fenyes for this great APOD. And congratulation, you also found a new super fast running star! ...this is yours..;-) https://live.staticflickr.com/65535/53159481124_3c382c6905_c.jpg DSS2 and todays APOD Image Credit & Copyright: Lorand Fenyes 2MASS 21011068+6807556 RAJ20...

It's notable to me that whereas the methane gas absorbs IR, the methane ice apparently reflects it! Is that due solely to the crystalline structure of the ice (molecules?) or for some other reason? Yes. The same reason why earth snow and clouds look white. Clouds of methane ice consist of methane c...

It's notable to me that whereas the methane gas absorbs IR, the methane ice apparently reflects it! Is that due solely to the crystalline structure of the ice (molecules?) or for some other reason? Webb’s Near-Infrared Camera (NIRCam) images objects in the near-infrared range from 0.6 to 5 microns,...

... Well. I don't want to come off as forensic after yesterday. But this APOD is also a mixture, today of a Webb AND a Hubble image, I call them WEBBLE. The original can probably be found at https://www.flickr.com/photos/196439708@N03/53098093285/in/photostream/ and is protected by copyright. At th...

But photons don't slow down. They only have one speed... c. Actually they do. Strictly speaking, "c" specifies the velocity only within a vacuum. The speed of light within a material having index of refraction n is the speed of light in a vacuum ÷ n (c/n). Also, Cherenkov radiation occurs...

The light of hydrogen link says: Why is the wavelength slightly shorter in air? Index of refraction,n, >1 (vacuum = 1), light slows down by c/n, photon energy is constant therefore frequency remains unchanged, so wavelength is shorter. But photons don't slow down. They only have one speed... c. Act...

The light of hydrogen link says: H-alpha (Hα) is a deep-red visible spectral line of the hydrogen atom with a wavelength of 656.28 nm in air and 656.46 nm in vacuum . It is the first spectral line in the Balmer series and is emitted when an electron falls from a hydrogen atom's third- to second-low...

How nice that this images preserves the "man in the Moon" mystique by endowing the Moon with evocative smokey facial features! (Hmm, are those smoke clouds or am I also seeing the underlying dark Maria?) And just look at all those new "canals" the Moon has! :ssmile: A mixed bag ...

Not sure I understand your geometry. What axis "through its handle"? A non-zero quadrupole rotation component is required for GW generation. A symmetrical dumbbell has two fundamental rotation axes that generally describe all rotation possibilities: Parallel and perpendicular to the dumbb...

Two bodies orbiting each other create waves in the plane of their orbit. A rotating body produces no gravitational radiation if it is spherical. Otherwise it does. And a dumbbell-shaped body rotating about a line through its "handle"? At what point does "two bodies orbiting each othe...

Thanks guys. So, is it only changing gravitational fields that produce GWs? Does a single mass moving alone in space produce GWs? How about one mass orbiting another: does that always produce GWs? Is the Earth's orbit around the Sun creating GWs? It is accelerating masses that produce GWs. And exte...

Nanoherz GW detection is "not trivial". 200 collaborators, 70 institutions, very small variations in timing due to several factors, directional-dependent "synchronization" errors and 15 years of observations yields a 3-σ confidence error (0.001 random chance). Optimistic to reach...

I don't see that. We're always at the center of a (nearly) circular path, and all that changes is the tilt with respect to the horizon. I just commented because I thought jisles was talking about the apparent motion of the sun, which can be described as a function of the latitude of the place of ob...

https://apod.nasa.gov/apod/image/2306/baltic-sea-timelapse-image_with-timescale600.jpg Beautiful picture! But I very much recommend the vimeo ! That can't possibly be correct. In the vimeo, which was shot in Sweden, it seems to get dark around 8 p.m., and the Sun seems to rise around 6 a.m. It's no...

https://apod.nasa.gov/apod/image/2306/baltic-sea-timelapse-image_with-timescale600.jpg Beautiful picture! But I very much recommend the vimeo ! APOD Robot wrote: To construct the timelapse image, 3296 video frames were recorded on the night of June's Full Moon between 7:04pm and 6:35am local time. ...

I wonder what the field of view is for background galaxy distribution and would-be filaments and clusters It must be smaller than 6 million ly because for large redshifts the more the distance (comoving radial distance) the more the angular size of the observed object. For a given angular size of t...

I like the new M87 radio (3.5 mm) image which includes the BH and the connected jets. Bystander posted about this new radio imaging, but I wanted to mention it again in this APOD. M87 BH and Jets - 3.5mm.jpg In the S&T article (Camille Carlisle), there are several links in addition to the Nature...

VictorBorun wrote: ↑Wed Apr 19, 2023 11:42 am wide-angle… 200°?

Yeah, wide angle ≈ 210°. I identified 11 stars horizontally across the middle of the image. The constellations of stars found include Lacerta (left edge), Cygnus, Lyra, Hercules, Corona Borealis, Bootes, Coma Bernices, Auriga, and Perseus (right edge).

How is it determined (or estimated I suppose) that Rigel is 74 times the radius of the Sun? By using the Stefan-Boltzmann Law, which states that a star's luminosity L is proportional to its radius^2 and temperature^4. It's been a (long) while since I crunched these numbers myself, but you can deter...

So the question I have is given this test and assuming the same impact conditions, how, far away or months of lead time, would be required for Dimorphos to miss Earth if it were on a direct collision course with us? This is a very specific case but one that this question should be answerable.