Search found 2955 matches
- Wed Jul 15, 2020 3:43 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
- Replies: 28
- Views: 8040
Re: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
With a telescope there's an objective lens and an eyepiece, and dividing the focal length of the former by the focal length of the later gives you the "magnification", and you also have to "focus" the image in order to see it clearly. Yet I see articles about the "afocal me...
- Wed Jul 15, 2020 3:41 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
- Replies: 28
- Views: 8040
Re: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
Telescopes are afocal. They have no focal plane- you can't hold a screen behind the eyepiece and see an image. What is coming out of the eyepiece is a fairly collimated bundle of rays. This enters your eye, and the lens in your eye brings the image to a focus on your retina. Afocal photography work...
- Wed Jul 15, 2020 3:28 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
- Replies: 28
- Views: 8040
Re: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
Hello all, I took this image, the 1500mm focal length can easily be explained by me pressing the 0 one too many times. It's 150mm focal length. If anyone wants to see where it was taken from, it was the south side of the A303 south and slightly west of Stonehenge. Thanks for that clarification on t...
- Tue Jul 14, 2020 9:37 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
- Replies: 28
- Views: 8040
Re: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
"Magnification" is a meaningless concept photographically. Hmm. Is that because you can blow up a photograph after taking it to simulate any magnification you want? Magnification is essentially an angular measurement, one that involves telescopic optics- that is, an optical system with bo...
- Tue Jul 14, 2020 7:47 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
- Replies: 28
- Views: 8040
Re: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
Another impressive comet pic, but, as usual, one that belies what you can see with your own eyes. The image details reveal: Camera: @Canonuk EOS Ra Lens: @SigmaPhoto 150-600mm f/5-6.3 DG HSM Focal length: 1500mm Aperture: f/5 Iso: 1600 Shutter speed: 30s for sky; 15s for foreground . That lens is a...
- Tue Jul 14, 2020 3:12 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
- Replies: 28
- Views: 8040
Re: APOD: Comet NEOWISE over Stonehenge (2020 Jul 14)
https://apod.nasa.gov/apod/calendar/S_200714.jpg Comet NEOWISE over Stonehenge Explanation: Have you ever seen a comet? Tonight -- and likely the next few nights -- should be a good chance . Go outside just at sunset and look to your northwest. The lower your horizon, the better. Binoculars may hel...
- Mon Jul 13, 2020 5:13 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet NEOWISE Rising over the Sea... (2020 Jul 13)
- Replies: 13
- Views: 6779
Re: APOD: Comet NEOWISE Rising over the Sea... (2020 Jul 13)
This comet is pretty spectacular I suppose, but I have to say I'm getting a little worried. Anyone here good at cometomancy? Does NEOWISE portend a quick end to the COVID-19 pandemic, or instead, prolonged misery for humanity? Comets portend disaster. This one is clearly running a good four years l...
- Mon Jul 13, 2020 5:09 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet NEOWISE Rising over the Sea... (2020 Jul 13)
- Replies: 13
- Views: 6779
Re: APOD: Comet NEOWISE Rising over the Sea... (2020 Jul 13)
This comet is pretty spectacular I suppose, but I have to say I'm getting a little worried. Anyone here good at cometomancy? Does NEOWISE portend a quick end to the COVID-19 pandemic, or instead, prolonged misery for humanity? The COVID-19 pandemic can't be left to cometomancy pseudo-science :!: Su...
- Mon Jul 13, 2020 3:55 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet NEOWISE Rising over the Sea... (2020 Jul 13)
- Replies: 13
- Views: 6779
Re: APOD: Comet NEOWISE Rising over the Sea... (2020 Jul 13)
https://apod.nasa.gov/apod/calendar/S_200713.jpg Comet NEOWISE Rising over the Adriatic Sea Explanation: This sight was worth getting out of bed early. Comet C/2020 F3 (NEOWISE) has been rising before dawn during the past week to the delight of northern sky enthusiasts awake that early. Up before s...
- Sun Jul 12, 2020 3:37 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Comet CG Creates Its Dust Tail (2020 Jul 12)
- Replies: 13
- Views: 3621
Re: APOD: Comet CG Creates Its Dust Tail (2020 Jul 12)
Do the jets impart a net thrust on the nucleus sufficient to change its trajectory or rate or axis of rotation over time? Has data been obtained on jet locations, composition and velocity sufficient to calculate mass flow rates and resulting thrust vectors? There seems to be some similarity to spac...
- Sat Jul 11, 2020 10:04 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
- Replies: 21
- Views: 10875
Re: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
As for why we don't see a green coma with NEOWISE, I'm not sure. Really bright comets (that is, naked eye) don't usually have obvious green comas, because the bright reflected sunlight from dust overwhelms the much dimmer green glow. All those pretty comets with their green comas are more gassy tha...
- Sat Jul 11, 2020 10:03 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
- Replies: 21
- Views: 10875
Re: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
Neat. I've been looking for a comet with a green ion tail - because why couldn't there be one? - but I haven't found any. Maybe there's a reason? As for why we don't see a green coma with NEOWISE, I'm not sure. Maybe it needs to be closer to the sun? But having things line up so that sunlight hitti...
- Sat Jul 11, 2020 7:58 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
- Replies: 21
- Views: 10875
Re: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
🌞☄️ Ann Thanks - cool site! (and very appropriate emojis) And now I have to ask the obvious follow-up: is it always primarily carbon monoxide ions (and why would that be, unless all comets are made up of the same stuff, which I find hard to believe), or have there been other comets with different c...
- Sat Jul 11, 2020 5:21 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
- Replies: 21
- Views: 10875
Re: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
https://apod.nasa.gov/apod/calendar/S_200711.jpg The Tails of Comet NEOWISE Explanation: Comet NEOWISE (C/2020 F3) is now sweeping through northern skies . Its developing tails stretch some six degrees across this telescopic field of view , recorded from Brno, Czech Republic before daybreak on July...
- Sat Jul 11, 2020 4:56 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
- Replies: 21
- Views: 10875
Re: APOD: The Tails of Comet NEOWISE (2020 Jul 11)
https://apod.nasa.gov/apod/calendar/S_200711.jpg The Tails of Comet NEOWISE Explanation: Comet NEOWISE (C/2020 F3) is now sweeping through northern skies . Its developing tails stretch some six degrees across this telescopic field of view , recorded from Brno, Czech Republic before daybreak on July...
- Thu Jul 09, 2020 4:35 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Noctilucent Clouds and Comet NEOWISE (2020 Jul 09)
- Replies: 15
- Views: 9172
Re: APOD: Noctilucent Clouds and Comet NEOWISE (2020 Jul 09)
If that comet is just visible to the unaided eye than then how would anybody even know those noctilucent clouds were even there with the unaided eye? Noctilucent clouds with dark clouds like letters July 5 2020.jpg Noctilucent clouds can be really bright, and they are often very extended. I took th...
- Thu Jul 09, 2020 2:44 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Mercury's Sodium Tail (2020 Jul 08)
- Replies: 20
- Views: 5016
Re: APOD: Mercury's Sodium Tail (2020 Jul 08)
Every body in the Solar System has a tail, because every body is losing atoms to the surrounding space, and there are directional fields and forces present everywhere. But in most cases, these tails are extremely rarefied. Every body? Even small rocky satellites of the outer planets, or asteroids i...
- Thu Jul 09, 2020 2:42 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Mercury's Sodium Tail (2020 Jul 08)
- Replies: 20
- Views: 5016
Re: APOD: Mercury's Sodium Tail (2020 Jul 08)
Every body in the Solar System has a tail, because every body is losing atoms to the surrounding space, and there are directional fields and forces present everywhere. But in most cases, these tails are extremely rarefied. I'm pretty sure my "body" doesn't have a tail (visible, anyway), a...
- Wed Jul 08, 2020 9:50 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Mercury's Sodium Tail (2020 Jul 08)
- Replies: 20
- Views: 5016
Re: APOD: Mercury's Sodium Tail (2020 Jul 08)
Unlike Mars & Mercury, Earth has both a high escape velocity and a protective magnetic field. <...much snipped...> Despite all that good info, I'm still not clear on whether earth has a tail or not. It is "losing" both hydrogen and helium at fairly low rates, and that these come to ma...
- Wed Jul 08, 2020 6:00 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Mercury's Sodium Tail (2020 Jul 08)
- Replies: 20
- Views: 5016
Re: APOD: Mercury's Sodium Tail (2020 Jul 08)
Surely Earth should have a tail, too? Unlike Mars & Mercury, Earth has both a high escape velocity and a protective magnetic field. <...much snipped...> Despite all that good info, I'm still not clear on whether earth has a tail or not. It is "losing" both hydrogen and helium at fairl...
- Mon Jul 06, 2020 6:32 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Saturn's Northern Hexagon (2020 Jul 05)
- Replies: 21
- Views: 5756
Re: APOD: Saturn's Northern Hexagon (2020 Jul 05)
If anyone did not know Saturn's strange hexagon recreated in the lab. ... Saturn's Hexagon Recreated in the Laboratory Emily Lakdawalla | Planetary Society | 2010 May 04 A Laboratory Model of Saturn’s North Polar Hexagon ~ Ana C. Barbosa Aguiar et al Icarus 206(2):755 (Apr 2010) DOI: 10.1016/j.icar...
- Sat Jul 04, 2020 2:23 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Meeting in the Mesosphere (2020 Jul 04)
- Replies: 10
- Views: 3219
Re: APOD: Meeting in the Mesosphere (2020 Jul 04)
Two great videos to watch here: https://www.youtube.com/watch?v=sQH6Oo4hn94 https://www.youtube.com/watch?v=tGPQ5kzJ9Tg The first video (from NASA) focuses on blue jets, yay! The other one, made by amateurs, explains a lot about red sprites (mostly) and some of the blue phenomena involved. I find b...
- Fri Jul 03, 2020 6:55 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Lynds Dark Nebula 1251 (2020 Jul 03)
- Replies: 15
- Views: 3279
Re: APOD: Lynds Dark Nebula 1251 (2020 Jul 03)
I found the nice picture at left of LDN 1251 and friends! :D Note the PGC and LEDA galaxies. The picture is not as deep as the APOD, so we don't see any Herbig-Haro objects or small stars with jets. Note the HD numbers of some of the stars, and the Dobashi designations of some of the extra-dark clo...
- Fri Jul 03, 2020 4:20 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: Lynds Dark Nebula 1251 (2020 Jul 03)
- Replies: 15
- Views: 3279
Re: APOD: Lynds Dark Nebula 1251 (2020 Jul 03)
APOD Robot wrote: Distant background galaxies also lurk on the scene, buried behind the dusty expanse. Well, I found a possible background galaxy, which looks pretty much like a fine face-on spiral galaxy to me. (Or else it's just another patch of illuminated nebulosity.) Have you found any others?...
- Thu Jul 02, 2020 9:02 pm
- Forum: The Bridge: Discuss an Astronomy Picture of the Day
- Topic: APOD: The Galaxy, the Planet, and the Tree... (2020 Jul 02)
- Replies: 15
- Views: 3403
Re: APOD: The Galaxy, the Planet, and the Tree... (2020 Jul 02)
Hi, Sp0ck! 🖖 You're right, there are a pair of interesting streaks there. The longer, fainter streak looks like some kind of imagery flaw or mistake to me, and the shorter, brighter streak baffles me. Well, maybe it's a satellite. That short streak looks especially strange because it seems to pass ...