Comments and questions about the
APOD on the main view screen.
-
APOD Robot
- Otto Posterman
- Posts: 5493
- Joined: Fri Dec 04, 2009 3:27 am
-
Contact:
Post
by APOD Robot » Sat May 26, 2018 4:05 am
Titan: Moon over Saturn
Explanation: Like Earth's moon,
Saturn's largest moon Titan is locked in synchronous rotation.
This mosiac of images recorded by the Cassini spacecraft in May of 2012 show's its anti-Saturn side, the side
always facing away from the ringed gas giant. The only moon in the solar system with a dense atmosphere, Titan is the only
solar system world besides Earth known to have standing bodies of liquid on its surface and an earthlike cycle of
liquid rain and evaporation. Its high altitude layer of atmospheric haze is evident in the Cassini view of the 5,000 kilometer diameter moon over Saturn's rings and cloud tops.
Near center is the dark dune-filled region known as Shangri-La. The Cassini-delivered Huygens probe rests below and left of center, after the
most distant landing for a spacecraft from Earth.
-
scr33d
- Ensign
- Posts: 40
- Joined: Tue Jun 05, 2012 2:37 pm
Post
by scr33d » Sat May 26, 2018 5:42 am
It just so happened that yesterday I started to re-read Imperial Earth, by Clarke...
-
heehaw
Post
by heehaw » Sat May 26, 2018 9:47 am
After all these decades as an astronomer, first amateur then professional, I only became aware TODAY, from APOD, that Titan rotates synchronously!
-
De58te
- Commander
- Posts: 584
- Joined: Mon Sep 30, 2013 6:35 pm
Post
by De58te » Sat May 26, 2018 11:07 am
heehaw wrote: ↑Sat May 26, 2018 9:47 am
After all these decades as an astronomer, first amateur then professional, I only became aware TODAY, from APOD, that Titan rotates synchronously!
That's probably because until Cassini's visit, nobody could tell if Titan was tidally locked because its dense atmosphere prevented anybody from seeing a surface feature. It was just presumed since all other major satellites are tidally locked to their primary.
-
neufer
- Vacationer at Tralfamadore
- Posts: 18805
- Joined: Mon Jan 21, 2008 1:57 pm
- Location: Alexandria, Virginia
Post
by neufer » Sat May 26, 2018 11:42 am
De58te wrote: ↑Sat May 26, 2018 11:07 am
heehaw wrote: ↑Sat May 26, 2018 9:47 am
After all these decades as an astronomer, first amateur then professional, I only became aware TODAY, from APOD, that Titan rotates synchronously!
That's probably because until Cassini's visit, nobody could tell if Titan was tidally locked because its dense atmosphere prevented anybody from seeing a surface feature. It was just presumed since all other major satellites are tidally locked to their primary.
Surface features on Titan were first identified in 1994 using infrared wavelengths on the newly refurbished Hubble Space Telescope.
25 moons are now
known to be Synchronously tidally locked.
Only Saturn's Phoebe & Hyperion and Jupiter's Himalia & Elara are
known not to be locked.
http://nineplanets.org/data1.html wrote:
Code: Select all
Radius Mass Rotate Dimensions
Name (km) (kg) Dens Abo Vo (days) (km)
--------- ------- ------- ---- --- ----- ------ ----------
Moon 1738 7.35e22 3.34 .12 -12.7 S
.....................................................................
Phobos 11 1.08e16 1.9 .06 11.3 S 13.5 x 10.8 x 9.4
Deimos 6 1.80e15 1.8 .07 12.3 S 7.5 x 6.1 x 5.5
.....................................................................
Metis 20 9.56e16 2.8 .05 17.5 ?
Adrastea 10 1.91e16 4.5 .05 18.7 ? 12.5 x 10 x 7.5
Amalthea 94 3.5 e18 1. .05 14.1 S 135 x 83 x 75
Thebe 50 7.77e17 1.5 .05 16.0 S 55 x 45
Io 1821 8.93e22 3.53 .61 5.0 S
Europa 1565 4.80e22 2.99 .64 5.3 S
Ganymede 2634 1.48e23 1.94 .42 4.6 S
Callisto 2403 1.08e23 1.85 .20 5.6 S
Leda 8 5.68e15 2.7 ? 20.2 ?
Himalia 93 9.56e18 2.8 ? 15.0 0.4
Lysithea 18 7.77e16 3.1 ? 18.2 ?
Elara 38 7.77e17 3.3 ? 16.6 0.5
Ananke 15 3.82e16 2.7 ? 18.9 ?
Carme 20 9.56e16 2.8 ? 17.9 ?
Pasiphae 25 1.91e17 2.9 ? 16.9 ?
Sinope 18 7.77e16 3.1 ? 18.0 ?
.....................................................................
Pan 10 ? ? .5 ? ?
Atlas 15 ? ? .9 18.0 ? 20 x 10
Prometheus 46 2.70e17 0.7 .6 15.8 ? 72 x 43 x 32
Pandora 42 2.20e17 0.7 .9 16.5 ? 57 x 42 x 31
Epimetheus 57 5.59e17 0.6 .8 15.7 S 69 x 55 x 55
Janus 89 1.98e18 0.65 .8 14.5 S 99 x 96 x 76
Mimas 199 3.75e19 1.14 .5 12.9 S
Enceladus 249 7.30e19 1.12 .99 11.7 S
Tethys 530 6.22e20 1.00 .9 10.2 S
Telesto 15 ? ? .5 18.7 ? 17 x 14 x 13
Calypso 13 ? ? .6 19.0 ? 17 x 11 x 11
Dione 560 1.05e21 1.44 .7 10.4 S
Helene 16 ? ? .7 18.4 ? 18 x 16 x 15
Rhea 764 2.31e21 1.24 .7 9.7 S
Titan 2575 1.35e23 1.88 .21 8.3 S
Hyperion 143 1.77e19 1.4 .3 14.2 chaotic 185 x 140 x 113
Iapetus 718 1.59e21 1.02 .2 11.1 S (y)
Phoebe 110 1.6 .06 16.5 0.4 115 x 110 x 105
.....................................................................
Cordelia 13 ? ? .07 24.0 ?
Ophelia 16 ? ? .07 24.0 ?
Bianca 22 ? ? .07 23.0 ?
Cressida 33 ? ? .07 22.0 ?
Desdemona 29 ? ? .07 22.0 ?
Juliet 42 ? ? .07 22.0 ?
Portia 55 ? ? .07 21.0 ?
Rosalind 27 ? ? .07 22.0 ?
Belinda 34 ? ? .07 22.0 ?
Puck 77 ? ? .07 20.0 ?
Miranda 236 6.59e19 1.20 .27 16.5 S 240 x 234 x 233
Ariel 581 1.35e21 1.67 .34 14.4 S 581 x 578 x 578
Umbriel 585 1.17e21 1.40 .18 15.3 S
Titania 789 3.53e21 1.71 .27 14.0 S
Oberon 761 3.01e21 1.63 .24 14.2 S
Caliban 40 .07 21.9
Stephano 15 .07 24.3
Sycorax 80 .07 20.4
Prospero 20 .07 23.2
Setebos 20 .07 23.3
.....................................................................
Naiad 29 ? ? .06 25.0 ?
Thalassa 40 ? ? .06 24.0 ?
Despina 74 ? ? .06 23.0 ?
Galatea 79 ? ? .06 23.0 ?
Larissa 96 ? ? .06 21.0 ? 104 x 89
Proteus 209 ? ? .06 20.0 ? 218 x 208 x 201
Triton 1353 2.15e22 2.05 .7 13.6 S
Nereid 170 ? ? .2 18.7 ?
.....................................................................
Charon 603 1.52e21 1.72 .32 15.5 S (z)
Nix 23 < 2e18 ? ? 22.9 ? (z)
Hydra 30 < 2e18 ? ? 23.4 ? (z)
----------------------------------------------------------------
Art Neuendorffer
-
Rusty Brown in Cda
Post
by Rusty Brown in Cda » Sat May 26, 2018 12:54 pm
"...show's its anti-Saturn side..."
They're putting apostrophes in verbs now?
-
Steve Dutch
Post
by Steve Dutch » Sat May 26, 2018 3:20 pm
Note how you can see a zone where the rings are visible but distorted by Titan's upper atmosphere.
Cassini was the most awesomely perfect mission ever flown.
-
ta152h0
- Schooled
- Posts: 1399
- Joined: Mon Aug 29, 2005 12:46 am
- Location: Auburn, Washington, USA
Post
by ta152h0 » Sat May 26, 2018 8:47 pm
I don't remember ever seeing this before. Keep posting images never seen before, like F4 Phantoms chasing Gemini 2 launches.
Wolf Kotenberg
-
ta152h0
- Schooled
- Posts: 1399
- Joined: Mon Aug 29, 2005 12:46 am
- Location: Auburn, Washington, USA
Post
by ta152h0 » Sat May 26, 2018 8:48 pm
You are all supercalifragicetc !
Wolf Kotenberg
-
heehaw
Post
by heehaw » Sat May 26, 2018 10:10 pm
A couple of moons, as I recall, are chaotic in their rotation! What if our own Moon had been chaotic in its rotation! Whee!
-
Beechy
- Asternaut
- Posts: 1
- Joined: Sat May 26, 2018 11:47 pm
Post
by Beechy » Sun May 27, 2018 12:12 am
Is the visible line, the high altitude haze that's mentioned? Why is it visible?
-
saturno2
- Commander
- Posts: 762
- Joined: Wed Jun 29, 2011 10:05 pm
Post
by saturno2 » Sun May 27, 2018 2:02 am
Titan is a Moon very interesting because
it has atmosphere and liquids on the surface
-
neufer
- Vacationer at Tralfamadore
- Posts: 18805
- Joined: Mon Jan 21, 2008 1:57 pm
- Location: Alexandria, Virginia
Post
by neufer » Mon May 28, 2018 5:30 pm
Beechy wrote: ↑Sun May 27, 2018 12:12 am
Is the visible line, the high altitude haze that's mentioned? Why is it visible?
https://www.etymonline.com/word/haze wrote:
haze (n.) "
opaqueness of the atmosphere," 1706, probably a back-formation of hazy (q.v.). Sense of "confusion, vagueness" is 1797. The differentiation of haze, mist, fog (and other dialectal words) is unmatched in other tongues, where the same word generally covers all three and often "cloud" as well; this may be an effect of the English climate on the English language.
hazy (adj.) 1620s, hawsey, nautical, of unknown origin. Some connect it with German hase "hare," an animal which plays an important part in Germanic folklore, with many supernatural and unlucky aspects in medieval times (among the superstitions:
a dead hare should not be brought aboard a fishing ship, and the word hare should not be spoken at sea). Another suggestion is Old English hasu, haswe "gray."
Art Neuendorffer