<article>
<h2 id="til-1-movement-in-the-galaxy-and-mass-extinctions">TIL 1:
Movement in the galaxy and mass extinctions</h2>
<ul>
<li>Throughout the history of this planet there have been a number of
mass extinctions. There are various theories about what has caused this.
I came across one of these recently.</li>
<li>The solar system doesn't orbit the galaxy in parallel with the
orientation of the galactic plane. There is a difference in the two
orientations in other words. Sometimes it's in the galactic plane, and
at times it's "above" or "below".</li>
<li>When in the plane the solar system is more protected from gamma ray
bursts originating in the galaxy than when it's not. The period of
rotation is the <em>Galactic year</em> and is about 225 million years
long.</li>
<li>The thinking is that when less protected perhaps the cosmic
radiation has effects on life on Earth. There seems to be a correlation
between these events - gamma ray exposure and extinctions - though there
is no certainty that this is so. Extinctions may have multiple causes,
so the relationship cannot be simple.</li>
<li>I have provided a few links that might give useful leads if you want
to find out more.</li>
</ul>
<h2 id="til-1-links">TIL 1: Links</h2>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Extinction_event">Wikipedia:
Extinction event</a></li>
<li><a href="https://en.wikipedia.org/wiki/Galactic_plane">Wikipedia:
Galactic plane</a></li>
<li><a href="https://en.wikipedia.org/wiki/Galactic_year">Wikipedia:
Galactic year</a></li>
<li><a
href="https://physics.stackexchange.com/questions/276958/what-angle-does-our-solar-system-make-with-the-milky-way">Physics
Stackexchange: What angle does our Solar System make with The Milky
Way?</a></li>
<li><a href="https://en.wikipedia.org/wiki/Shiva_hypothesis">Wikipedia:
Shiva hypothesis</a></li>
<li><a
href="https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/abs/galactic-cycle-of-extinction/DE684156C04E767E8C2F10284E9CAA3F">International
Journal of Astrobiology: <em>The galactic cycle of
extinction</em></a></li>
</ul>
<h2 id="til-2-which-is-correct---ml-or-ml">TIL 2: Which is correct -
<code>ml</code> or <code>mL</code>?</h2>
<ul>
<li>What is the correct abbreviation for <em>millilitre</em>?</li>
<li>I watch a YouTube channel about cooking, from Canada. It is <a
href="https://www.youtube.com/@GlenAndFriendsCooking">Glen and Friends
Cooking</a></li>
<li>The show ends with a recipe, and in some cases the measurements are
metric. Often it's something like <em>540 mL can of tomatoes</em>.</li>
<li>Having done Chemistry at school and university we were taught the
abbreviated form of <em>millilitre</em> is <em>ml</em>, but today I
learnt that mixed case <em>mL</em> is also permitted and is preferred in
the USA, Canada and Australia, while Europe prefers lower case
<em>ml</em>.</li>
<li>It's a similar situation with other fractions and multiples of a
Litre such as <em>dl</em> and <em>dL</em> for <em>decilitre</em> and
even for <em>quettalitre</em> (10<sup>30</sup> litres) - <em>Ql</em> and
<em>QL</em>.</li>
</ul>
<h2 id="til-2-links">TIL 2: Links</h2>
<ul>
<li><a href="https://www.youtube.com/@GlenAndFriendsCooking">Glen and
Friends Cooking</a></li>
<li><a
href="https://en.wikipedia.org/wiki/Litre#SI_prefixes_applied_to_the_litre">Wikipedia:
SI prefixes applied to the litre</a></li>
</ul>
<h2 id="til-3-meibomium-glands">TIL 3: Meibomium glands</h2>
<ul>
<li>These glands are a type of sebaceous gland in the eyelid. Sebaceous
glands in general produce secretions to protect the skin and hair. On
the skin they are part of the hair follicle and produce an oily
substance called <em>sebum</em> (from the Latin word for <em>tallow</em>
used to make candles).</li>
<li>The Meibomium glands are found along the edge of the eyelid adjacent
to the eyelashes. The oily substance they produce helps to prevent the
eye surface from drying out by mixing with the tears. It also helps the
eyelids to make an airtight seal when the eyes are closed. There are
many functions.</li>
<li>I knew about the Meibomium glands from learning about human anatomy
as a student, but didn't know very much about their function.</li>
<li>The glands are named after Heinrich Meibom (1638 – 1700), a German
physician and scholar.</li>
<li>I didn't know that the secretions produced by these glands can
reduce with age, or the glands can can be blocked, leading to MGD
(<em>Meibomium Gland Dysfunction</em>). I might have this according to
my Optometrist.</li>
<li>I also didn't know that the secretion has a name:
<em>meibum</em>.</li>
</ul>
<h2 id="til-3-links">TIL 3: Links</h2>
<ul>
<li><a href="https://en.wikipedia.org/wiki/Sebaceous_gland">Wikipedia: Sebaceous gland</a></li>
<li><a href="https://en.wikipedia.org/wiki/Meibomian_gland">Wikipedia:
Meibomium gland</a></li>
<li><a
href="https://en.wikipedia.org/wiki/Heinrich_Meibom_(doctor)">Wikipedia:
Heinrich Meibom</a></li>
<li><a
href="https://en.wikipedia.org/wiki/Meibomian_gland_dysfunction">Wikipedia:
Meibomium Gland Dysfunction</a></li>
</ul>
</article>
