Finally caught a glimpse of some of the European bison that roam around the Zuid-Kennemerland national park just north of Zandvoort 🦬🙂

This pair were splashing around in a small pond, then wandered off into the dunes.

As seen during this evening’s 90km ride.

#cyclinglife 🚴‍♂️
The Kraansvlak herd of bison or “wisent” have free run of quite a large area of the dunes & are monitored as part of a rewilding research project. Despite the old idea that they’re predominantly forest animals, they do very well in this setting.

wisenten.nl/en
Some of the bison are fitted with GPS collars & you can check this map to see where they are. I did that when I reached Zandvoort, saw that some were close to one of the bike paths that go through the park, so I went looking.

wisenten.nl/en/where-are-t…
One of them was standing high on a dune close to the fence & I was thrilled, but before I could get my phone out, it saw me & wandered down behind the dune. I heard it mooching around in a little lake, but couldn’t see it. Then it & another emerged, so I grabbed a shot.
In the winter, it’s possible to walk through their fenced-off park, but between 1 March & 1 September, it’s closed off as they get territorial. They’re very big & can be dangerous. So I was lucky this evening that these were near the fence & bike path 👍
And to finish, here’s a little bit of video showing them slowly ambling off into the dunes. I’m not sure how large the full herd is: 20-30, I think, but it changes as they exchange bison with other projects around Europe.
p.s. This location is within a kilometre of the north end of the Zandvoort race track, so probably gets a noisy when petrolheads like @DrCaplin are there, as she was earlier today.

I thought of her when I saw a smashed up Ferrari road car being trucked away from the track 🤷‍♂️

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More from @markmccaughrean

Mar 30
Perhaps the most distant known star, detectable by Hubble thanks to gravitational lensing.

Or is it a star in our own Milky Way that just happens to lie on the lensing caustic?

The good news: #JWST will get a spectrum & tell us one way or the other 🤷‍♂️

bbc.com/news/science-e…
The authors have ruled out the latter by suggesting that a star in our own galaxy would likely have moved a bit in the 3.5 years since its discovery.

Perhaps, but in a semi-random distribution of motions, not all stars move tangentially; some will move mostly radially.
That’s the problem with the detection of a single object – statistical arguments about the possibility of finding such & such an object right at a given spot are not always going to be kind to you. It depends on how many places you’ve looked for such objects as well.
Read 11 tweets
Jan 24
Venus & Mercury, closer to the Sun, orbit more quickly, in 225 & 88 Earth days, respectively.

Mars is further out & takes 687 days to orbit; Jupiter 4332, Saturn 10759, Uranus 30685, & Neptune 60,189 days.

Ditto for non-planets like Pluto. Cough 😳

Image: Wikipedia/WP

18/
The relationship between the distance of a planet from the Sun & its orbital period was discovered by Johannes Kepler.

His third law says the square of the orbital period of a planet is proportional to the cube of its orbital semi-major axis.

19/

So, if your orbit is a bit further from the Sun than Earth's, you'll orbit a bit more slowly.

So, at 1.5 million km further out than Earth (i.e. 1% larger than Earth's orbit), you'd take 1.5% longer to go around the Sun, i.e. 370.74 days.

20/
Read 27 tweets
Jan 24
A few hours from now, #JWST will make its Mid-Course Correction 2 (MCC-2) burn, injecting it into its operational orbit around the Sun-Earth L2 point, ~1.5 million kilometres away.

What, why, how, when?!

A thread.

1/
First, a reminder: #JWST was launched on #Ariane5 #VA256 from Europe's spaceport in French Guiana on 25 December 2021. The #Ariane5 put it on a near-perfect trajectory towards L2 & two subsequent JWST Mid-Course Corrections have tweaked that.

2/
But why such a long journey to a place that's about four times further away from Earth than the Moon?

By contrast, the Hubble Space Telescope is in a low Earth orbit ~535km above the surface, making it accessible to several servicing missions over the past 31 years.

3/
Read 19 tweets
Jan 8
As the start of the last major #JWST deployment approaches, the starboard primary mirror wing, it's time for a thread about what that helps enable – excellent spatial resolution.

It's #SharpnessSaturday (yes, the hashtag symbol also denotes a "sharp" in music 🙂)
So what do we mean by "spatial resolution"?

It's a way of quantifying the sharpness of an image scene, the amount of detail visible at small scales, or at some rather fundamental level, how close two things can be in a scene & still be separated.

2/
For astronomers, that's often simplified to saying "how close can two stars of equal brightness be on the sky & still separable or resolvable?"

That's not to say the stars need actually be close in space, but just how they appear on the sky.

3/
Read 34 tweets
Jan 8
And … as one third of you got right, the correct answer is “Glass” 🙂

Yes, even though the beryllium mirrors of #JWST are coated with a highly infrared reflective 100nm layer of gold, that in turn is coated with a thin layer of SiO2 (aka silica) to protect it from dings.

1/
Gold is soft & easily scratched, hence the overcoat. Silica is used in many applications, but in this form, it’s reasonable to refer to it as glass.

Of course, almost all photons hitting #JWST pass straight through before hitting & getting reflected by the gold, but still.

2/
A little more information here

jwst.nasa.gov/content/observ…

and here

laserfocusworld.com/test-measureme…

and thanks again to @apolitosb for posing the question. What we haven’t found out yet is how thick the SiO2 layer is – probably similar to the 100nm of gold, but more exactly … 🤷‍♂️

3/3
Read 4 tweets
Jan 7
Today’s the day – #JWST starts spreading the wings around its eyes 👀

And yes, I know this joke would make more sense if this was a pit viper rather than a cobra, but they don’t have a deployable hood 🐍🤷‍♂️

1/
That is, cobras are members of the elapid family of snakes, whereas pit vipers, including rattlesnakes, are from the crotaline family.

And what pit vipers share with boas & pythons is an ability to sense the infrared, which cobras lack.

2/
Not with their eyes, but via specialised “pit organs” near their snout. These hold a thin membrane with many nerve endings & blood vessels: the former sense infrared light (aka heat) between 5 & 30 microns, & the latter cool the membrane to refresh it.

en.m.wikipedia.org/wiki/Infrared_…
Read 14 tweets

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