Gfamily

9 hours ago, andrew s said:

Yes it has to directly "impact" the BH event horizon.  As you point out it can't join the accretion disc. Not sure it's a unique insight though.

Regards Andrew 

Yes, the DM needs to impact the event horizon,  but a significant difference with a BH is that the 'cross section area' of the black hole is proportional to the square of the mass, (rather than the ⅔ power or less for stellar/planetary bodies), and also that any infalling DM will have no obstructions to impacting the event horizon, in contrast to OM which will generally have to negotiate the accretion disc and potentially high magnetic fields in the vicinity of the BH. Given that we often detect BHs via their emission of radio and X rays from jets, much infalling OM fails to make it to the event horizon.

So primordial supermassive BHs could potentially accrete DM significantly faster than ordinary matter.

One difference between ordinary matter (OM) and dark matter (DM) is the way that OM can aggregate together.

If you consider a piece of OM on the edge of the Milky Way or the Solar System. The material at the outside has a lot of gravitational potential, and when it falls in it converts the gravitational potential energy into kinetic energy (it speeds up) and after passing through the inner Solar System It heads back out and slows down. 

However, if it hits something in the middle, it'll give up some of its kinetic energy as heat and the light that hot objects give off. This means that after the collision, the OM won't go as far out and thus the Ordinary Matter collects in the centre of the Solar System.

The means of aggregation is the conversion of kinetic energy into light (electromagnetic energy) which is then lost from the system.

Because Dark Matter does not participate in any process involving electromagnetic energy, it doesn't have a way of losing energy, so any DM that falls towards the centre, simply passes through it and back out again with no means of aggregating there in the same way that OM can.

This means that the average density of DM in the inner Solar System remains very low (similarly in the inner reaches of the Milky Way there's no particular concentration). 

Interestingly, it seems that any DM that falls directly into the Supermassive Black Hole at the centre of a galaxy will be captured and will not escape - as far as I can tell, this is the only way of constraining DM. This last point is not one I've seen referenced anywhere, so it is my personal contribution to cosmology. If I was a better astronomer I'd have a clue how to apply this hypothesis to see if it's useful. 🙂

1 hour ago, badhex said:

Ooh don't they have a model of the 40-foot telescope there? Very topical for me as I'm also trying to track down Enceladus, albeit with a much smaller scope 😂

I don't think they have his 40ft scope, though they have one of his smaller (6" I think) scopes on display 

13 hours ago, Zermelo said:

There is also an excellent BBC radio series, 13 minutes to the moon.

From around episode 9 it covers the decent, including those 1201/1202 alarms).

The same team went on to do further episodes about the Apollo 13 story.

Following a successful Kickstarter, they're also in the process of putting together a new podcast series "Sixteen Sunsets" - title based on the number of sunrises and sunsets experienced by the astronauts and cosmonauts on the ISS each day.

https://sixteensunsets.com/

Be warned, that Saturn's rings are not going to be particularly prominent this year or for the next 2 or 3 years as their inclination angle is quite small. If you can get a 'scope this year, they'll be moderately well ❤️‍🩹 visible, but less so after that. However, Jupiter is a very rewarding alternative target, as it's bigger, has visible surface bands, and it's moons are constantly changing.

I'm terms of what telescope, I can recommend the Skywatcher 127mm Maksutov, mentioned above as it's got a long focal length, so will more easily give a larger image. 

It's also outstanding on the Moon. 

1 minute ago, lawsio said:

Also, I notice in the linked thread references to setting it up with an ADC. I don't have one - is that a major oversight or is it a nice to have?

An ADC is a nice to have, particularly if you're imaging planets relatively low to the horizon. As you may know, refraction through the Earth's atmosphere can behave like a prism, so you get red and blue fringes above and below the disc of the planet - this is Atmospheric Dispersion.  Not only above and below, but red and blue light from features on the disc, get 'smeared' across the disc.  If you're imaging without an ADC (AD Corrector), you can get some relief from this by letting your processing software realign the red and blue channels - this will help, but a better solution is to use an ADC, as this means that the camera sensor gathers the correct colour data in the correct place on the image.

Ian Morison (a good authority) has a page about this on his Astronomy Digest blog https://www.ianmorison.com/combating-atmospheric-dispersion/

Our daughter was age 2 when she called one of her dolls 'Baby Vega' and knew that it's the first star you can see on a summer evening. 

Ended up getting a Masters in Astrophysics from Edinburgh.

Good luck to yours. 

5 hours ago, wookie1965 said:

My maps says its 3hrs and 16minutes  181 miles to  Cwmdu Astrocamp

Quite literally, YMMV.

For the OP - if you look at the Events listing page of gostargazing.co.uk website, you can see events in your area. Some of these will be regular club meetings, others may be special public access events, which may offer the opportunity to do observing.

Of course, in the UK, the weather is a limiting factor, as planned events may not coincide with clear skies, but there's usually some alternative activities offered, as well as the chance to meet up with members of the local societies.

https://gostargazing.co.uk/stargazing-events/

On 01/09/2023 at 15:19, Mandy D said:

No, this is definitely not what I was referring to, as that is a solar transit. It is imagery of one of Mars' moons transiting the Sun. What I said was total eclipses of the Sun by the planet from it's moons.

Yes. I understood you to mean the equivalent of a lunar eclipse, where the moon goes into the shadow of the planet. 

Celestron do a 2x Barlow that has a T-thread at the top, for which the Barlow lens element can be removed. 

Very cheap and cheerful

On 02/08/2023 at 12:16, Maho said:

Hello all,

 

I've never been to astrocamp or a star party and I'm pretty much still learning about astronomy and astrophotography.

I dont actually have a campervan. Do people just come in their cars and sleep in it? I dont fancy investing in tent, sleeping bags etc. 

There is the option of finding a local hotel or B&B and buying an 'offsite' ticket. This way you can share in the daytime events and stay at late as you can in the evening.

There are places to park nearby on the main road with just a short walk to join us. Not ideal, but it's not uncommon for people to do. 

But, as people are saying, a tent, an air mattress and a decent sleeping bag are probably the cheapest way to get the most out of the weekend. Do you have anyone you could borrow from? (Ok, maybe get your own sleeping bag 😄 )

Edit: it's usual for people to set up their gear on The Common and just throw a waterproof cover over it when they're done. It's a very safe environment, so very little risk if you do. 

As a rule of thumb, I reckon it's better to consider the field of view rather than the 'magnification'.

The fov of a camera is similar to that of a Plossl eyepiece with the same focal length as the diagonal of the sensor. 

So an APS-C with a diagonal of ~28mm will give roughly the same fov as a 28-30mm eyepiece.

ETA: and your ASI seems to have a diagonal of about 12.5mm, so should give an idea of the fov to expect.

ETA2: of course I should have read all through the reply from @ONIKKINEN first.

Are you a member of an Astro Society (Macc Astro is highly regarded and near you)? If they have observing sessions, you may have a chance to look through other people's scopes and see what they're using.

Alternatively, we're looking towards the autumn Star Party season, so if you can free up a weekend, these can be good for meeting a variety of people and see a variety of scopes.  We're aiming to be at the Astrocamp Star Party near Crickhowell in September, bookings open next weekend (google Awesome Astrocamp) 

Personally, I have a 72mm refractor and a 127 Maksutov, both of which work on my AZ GTi - the refractor has a good wide angle field of view and GOTOs are always successful - for the Mak, I sometimes find that GOTOs can be a little off - so I sometimes have to hunt around to confirm the target in the FOV. I think it's the weight is a little more than the mount likes - but once the target is found it works OK.  I usually goto a bright star nearby, them SYNC, and then it's only a short hop to the target. 

There is a Celestron Barlow that has a T-thread at the top so you can easily attach a camera (mirrorless/DSLR). 

I have to say I'd not known about the ability to re-purpose the nosepiece lens from the Barlow on the ep or on the diagonal, but it makes sense and is something to try. Thanks @Don Pensack

Here's a suggestion list for Dark Skies camping from the uk campsites website

https://www.campsites.co.uk/search/dark-sky-campsites

A sheet of Baader solar film can be used to make a white light filter for solar observing. 

This can be mounted between two strips of card or similar, with the film held between them so they fit securely to the OTA. 

The RDF can be replaced by a solar finder, and if you have a 3D printer (or access to one), these can be easily made (or alternatively bodged with an offcut of wood and some plastic or metal strips).

Have you downloaded the Pro version of the SynScan App? That allows you to use the Point and Track mode for the Sun

For general use I'd also suggest getting a longer focal length eyepiece; the narrow field of view of a Mak is a given, and can make it frustrating if you're trying to find a target that's slightly off centre, ao a longer EP with a wider fov will help.

. 

Very nice capture.

Here's an animation of the eruption from the SDO Satellite 

As people may have heard, the deployment of the Radar for Icy Moons Exploration (RIME) antenna had been incomplete because a pin hadn't properly been released. RIME is one of the key instruments for Juice, as it will allow radar investigation of the sub surface to a depth of up to 9km.

Fortunately, after rotating the craft to allow sunlight to fall on the area with the stuck pin, and by firing a non explosive actuator, they were able to release the pin, and the 16m long antenna arm was released. 

ETA https://www.esa.int/Science_Exploration/Space_Science/Juice/Juice_s_RIME_antenna_breaks_free

Are you familiar with the binocularsky.com website - run by Steve Tonkin ( @BinocularSky here ) who writes about binoculars and what's to be seen through them for Astro magazines?

If you go to his site, there's a search page designed for binocular use, which suggests about 65 Messier targets available for 10x50s if your limiting magnitude is about 10m. 

https://binocularsky.com/search.php

Lots of great advice across the whole of his site.

And there's a monthly newsletter giving suggestions for binocular targets for that time of year. 

17 minutes ago, happylimpet said:

Thanks for replies so far all - and yes I have been considering driving it out there - at least for delivery! We have friends in Lyons, just 3hrs further down.....

The cost of ferry+fuel isnt hugely bigger than courier, and way less hassle.....

That's certainly handy were you to want to buy from one of the European astro dealers - arrange delivery to your friends, and pick them up and bring them back to UK as part of your personal allowance.  

Is it worth having a couple of short breaks to France - dropping it off on the first one, and picking it up a week or two later? 

You're already very convenient for ferries to Caen or Le Havre.  It's about 6 hours from either to Nevers, so doable with 1 overnight stop.  

Just to follow up on this - it seems that (according to the Mask Generator at https://satakagi.github.io/tribahtinovWebApps/Bahtinov.html ) the higher the f/ ratio, the larger the slits.

f/10 mask on the left

f/20 mask on the right

Does your mirrorless camera have a hot shoe bracket?  If so - you might be able to fashion a DIY mount to fix a cheap Red Dot finder - something like this one I made up  using an old RDF, an L bracket that I turned into a U bracket by hitting with a hammer, and a hot shoe foot from ebay. 

Obviously, the camera in this image is a dSLR, but if your mirrorless has the mount it might work for you.  

You could do that.

I think the biggest issue would be the reduction in light coming through, so you wouldn't benefit from shorter exposures for your 'focusing', but it should certainly be able to use it.  

I don't know for sure, but I get the impression there you would ideally have different thickness slits for different f/ ratios, but you could confirm this by using one of the online mask generator tools and putting different focal lengths for the same aperture, to see if the suggested masks are any different.  

3 hours ago, DaveS said:

A RUD on the OLM or shortly after lift off would have been a failure.

SpaceX will (Hopefully) learn from their mistakes and correct them. Rapid failure iterations appears to be the spaceX way.

But I think it doesn't matter what I say, you've already made up your mind.

So there was no failure - glad to have cleared that up to your satisfaction - at least !

So there were failures, and mistakes after all. 

But they'll learn from them.

There is the question of why the ones that were predicted beforehand (including the ones that were predicted as "we think this may be a mistake") were not catered for in advance?  And why that's not a 'failure'

EDIT

But good to know that I'm the one that's already made up their mind. lol!