George Jones

I just came in, and the last thing at which I looked was the Blue Snowball. I am sure that my 60-year-old eyes can see some tint in the image produced by my 8 inch SCT.

Welcome from Prince George BC.

Yes, these guys are outside our Local Group. They're being whisked away from us at about 700 kilometres (430 miles) per second by the expansion of the universe. Mind-boggling stuff!

Nothing relaxes me as much as my observing sessions do.

Years ago, while teaching an astronomy course to about 120 university students and talking about the light-gathering power of telescopes, I said "To some extent, it's not the length that matters, it's the width." The class broke into loud laughter. Ever since, I have been careful not to phrase it like this.

In the months leading up to COVID, I gave a couple of public talks on gravitational waves. I don't know if a non-maths talk on what's below would be interesting or appropriate.

Gravitational Waves and Gravitational Wave Astronomy

Gravitational waves, first observed in 2015, are produced when compact objects like black holes and neutron stars merge. Just as useful information can be extracted from light wave signals, useful information  also can be extracted from gravitational wave signals.

How long is a typical talk?

Me too!

Even if it does reach a conclusion, we might not like the conclusion. Paraphrasing  Planck: "Science advances one funeral at a time."

Actual version: "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it."

A CPC 1100 and a SkyShed POD.

21 hours ago, andrew s said:

we desperately need more data to constrain the speculation.

I agree., and over the next 10 years or so, we will accumulate a lot more data from the LHC, from experiments that attempt direct detection of dark matter, and from other observations. If, at the end of 10 years, we are still in a dark matter muddle, I think we will be in crisis mode. Other physicist would disagree, and would echo SuperTramp. Crisis? What Crisis?

Experimental data has already killed off substantial portions of "theory space" for dark matter. Theory space, however, is an expanding universe.

I meant to get to this earlier, but I have been doing a COVID-related overload, and things have been somewhat hectic.

The talk included theoretical results of the paper to which I linked in my previous post. The authors of the paper take the view that gravity is okay, and that new unseen and transparent dark matter is needed to account for the motions of stars in galaxies, and galaxies in clusters of galaxies. Observations of the relative abundances of primordial elements, and of the Cosmic Microwave Background (CMB), indicate that dark matter is not made of the particles that account for normal matter's mass, protons and neutrons.

To date, we only have evidence that dark matter interacts via gravity, but many physicist think/hope that dark matter interacts via other (quantum) forces. They think that dark matter has quantum interactions, because this would give scenarios for dark matter production in the early universe similar to the production of normal matter, e.g., matter antimatter annihilation/creation that continues until the universe expands enough to stop these processes. Physicists hope that dark matter interacts with normal matter, as this gives ways for experimentally seeing signatures of dark matter.

If there are other interactions (besides gravity) involving dark matter interactions, they could be between: 1) dark matter and dark matter (just as there are interactions between normal matter and normal matter), and/or 2) dark matter and normal matter.

The very interesting talk was about theoretical models that have both 1) and 2), where 1) is used to generate the masses of dark matter particles, and 2) is used to predict observable effects of the models.

Two scenarios were considered for generation dark matter mass. One was a possible a dark electromagnetic-like interaction between dark matter and dark matter. The analogy is not exact, as, unlike normal photons, the dark photons have mass that they acquire from a proposed dark Higgs-like particle. Another possibility is that there is a dark colour-like force. In the normal colour nucleon force, gluons carry the colour force, and thus gluons can interact with gluons. In the proposed dark colour-like interactions, dark gluons interact to form massive dark glueballls.

In both types of models, it is proposed that there is a "feeble" interaction between dark matter and normal matter. This feeble interaction can inject energy into the normal universe. If his injection is early enough, it can affect the relative primordial abundances of elements. If this energy injection is later, it can affect the the thermal spectrum of the CMB. If this injection is later still, it can affect the anisotropy spectrum of the CMB. High precision cosmological measurements could reveal these effects.

Possible results for the LHC and for high precision cosmological measurements probe complementary interaction strengths. The cosmological results are for weaker interactions.

My earliest memory of students taking pictures with mobiles is from 2006. I was teaching an electronics lab then, and students used their mobiles to take pictures of oscilloscope traces that they needed for their lab reports.

3 hours ago, andrew s said:

@George Jones please give us an update on the talk and your take on it.

Interested to here the  speakers view on why the LHC has not found any evidence for particles beyond the standard model . Other than the standard " they are beyond its energy range".

Regards Andrew 

The speaker is one of the authors of the recent paper

https://arxiv.org/abs/2003.02273

so I suspect the talk will be an upper-level undergrad version of this. He might not mention the LHC.

Today, at 1 pm local (9 pm BT), I will attend the following Zoom talk. Normally, the talk would be in-person, and I and other folks would get to talk with the speaker over a meal. Because of COVID, the talk is virtual. 🙁

"Title:  Searching for Dark Forces in the Cosmos

 Abstract:  New fundamental forces can play a crucial role in models of dark matter and they are predicted by many theories of particle physics beyond the Standard Model. Such new forces are said to be "dark" if they interact only very weakly with ordinary matter. They could take many forms, with specific examples being similar to the electromagnetic or strong forces, and in some cases they can even be the source of dark matter themselves. In this talk I will describe how such forces might arise and what they can do in the early universe. In particular, I will show how detailed measurements of primordial element abundances and the cosmic microwave background radiation can be used to search for them."

About four or five years ago, my daughter made a drawing of some Harry Potter characters in the bottom right corner of the board of my office. This is the only thing that doesn't get erased.

Bins in the house, NexStar 8SE on tripod in the shed.

22 hours ago, randomic said:

As a side note: counterintuitively, this means that you not only weigh less when the moon is directly overhead but also when the moon is directly underneath.

But weight isn't a tidal effect.

Welcome to SGL. I grew up a couple of hours from Toronto. Because of COVID, I didn't make it to Toronto this summer.

Welcome to a great forum. I do strictly visual, usually in the centre of Prince George BC. I last visited Calgary in summer 2019 when my family and another family camped near Banff.

I recommend some type of 10x50s. These are good general purpose bins (astronomy and daytime uses). I have 10x50s and 15x70s.

I have a NexStar 8SE, and for some time I have been considering getting a CPC 1100. I would dearly love to have a CPC 1100, (I would also keep my NexStar), but I am somewhat worried about the weight of the OTA/mount.

My specs: I will be 60 next month; I am 5' 5'' tall; I weigh 130 pounds; I am in good physical condition, and I don't mind lugging somewhat heavy stuff.

Thoughts?

Thanks.

These are the original boxes for my NexStar 8SE, which I got in the fall of 2009. Two years later, I used these boxes when I made a big move from one side of Canada to the other, 4100 kilometres (2500 miles) as the crow flies. Four years after that, I used them again when I made a small move from our flat to our current house, 3.4 kilometres (2.1 miles).

I teach physics (labs and lectures) and astronomy (lectures), and I mentor (post)grad students who make money teaching physics labs. I love all of this, so I pretty much have my dream job.

8 minutes ago, johnturley said:

I assume by local noon Corncrake meant the time when the sun transits, rather than local noon which would still be affected by the equation of time.

John 

I meant something more fundamental. Suppose Mike lives in the northern hemisphere between the Tropic of Cancer and the equator (as I did for two years). Where does Mike see the Sun on a date that is near June 20th, and at a time that is near local noon?

On 14/07/2020 at 00:22, Corncrake said:

In the northern hemisphere the sun is due south at local noon (not civil noon !) on any day**. Push a stick into the ground in your range and get your youngsters to mark its shadow during the day. it will be shortest at local noon.  If they do that each hour they will have a crude sundial

**Be careful though, strictly speaking the equinox is a moment in time and may not happen at your local noon, (the equinox it is not a day). So the direction of the sun AT the equinox may not be due south for you !

Be careful. As a general statement, your first sentence is FALSE.