botany - Online course on Plant Taxonomy and Physiology

Well, I wasn't able to find an online video course. The closest I came was this site, which links to courses that put their material online. Most of these are compilations of the lecture notes. There's also this page from the University of British Columbia, that has a nice little overview of the field of plant taxonomy.

In my experience, botany and plant identification are subjects where one really needs to learn by doing. You really need to grab a plant and take a close look at it while noting why its in the group that its in. A great way to get started might be to join a local gardening club or native plant society. The people in those groups can provide their tips for ID-ing plants.

One of the primary skills you'll want to learn is identifying what family a plant is in. Plant families have (mostly) consistent characters, and learning how to spot the most common families in your area will be a big help.

universe - Are black holes expanding?

Simple Answer

Large black holes are usually expanding by an incredibly small amount as they suck in more stuff (gases, planets, stars, etc.) through gravity. So they are expanding but not because of our expanding universe.

Exceptions

According to Wikipedia, small black holes might shrink. Stephen Hawking predicts that all black holes have radiation. Small black holes, that suck in less, might emit more energy than they pull in, so they theoretically shrink and close.

Big Asterisk

There are many additional details that could be included in this thread. I think the most important to point out is that fifty years ago black holes were still largely science fiction. So it's a relatively new science. And even if we had been studying them for 200-300 years, they're hard to observe and practically impossible to experiment with. Point being, most black hole knowledge is actually black hole theory.

Observing Black Holes

Here's a relevant Wiki excerpt:

In June 2008, NASA launched the Fermi space telescope, which is
searching for the terminal gamma-ray flashes expected from evaporating
primordial black holes. In the event that speculative large extra
dimension theories are correct, CERN's Large Hadron Collider may be
able to create micro black holes and observe their
evaporation.

Relevant Detail on Black Holes

Black holes were once massive stars. Stars have massive gravity but they don't collapse until they run out of fuel. When they do run out of fuel, they expand then collapse. Big stars have so much gravity that they collapse into a small sphere with gravity so intense that light can't escape it. That is when a black "hole" is born. Really, it's more like a black sphere. It appears to be a hole only because no light escapes. Inside the sphere there could be a hole, but no one knows.

Further Explanation on Black Hole Expansion

Bigger stars have more mass so when they collapse, they have more gravity and the perceived "hole" is bigger. Typically, large galaxies have large black holes at their center and small galaxies have small black holes. Over time, the black hole will pull more matter (gases, planets, asteroids, etc.) into its sphere of blackness. This adds to its mass and slowly increases its gravity. More gravity means a wider radius of black where from which not even light escapes.

Unanswered / Theorized

When does a black hole stop growing and why? That's hard to answer because we have no data about the inside of a black hole. Some people theorize the immense gravity bends space/time to create a wormhole. Many questions about space are being answered in our lifetime by observing and experimenting. Black holes are hard to observe and even harder to experiment with. Most "answers" in our lifetime will be more theory than proven physics.

star - Recommendation for learning about stellar astrophysics

I would like to know which are the best books to learn about stellar astrophysics at (just) graduate level.

I have a basic formation in general astrophysics but I'm interested in learning about stars, specially their evolution and constitution. I also have a good mathematical formation so it should not be a problem (but I don't care if it focus on the ideas as long as it is a good book and make itself clear).

I found several books at the university library, but I don't know which of them are good (in my situation at least).

milky way - How do we know that our galaxy is a spiral galaxy?

I know that our galaxy is spiral in shape, but I'm wondering how the scientists found out that our galaxy has a spiral shape.

I don't think we can see the entire galaxy from telescopes on Earth, right?

I think it makes sense that they say that Andromeda has a spiral shape because we can see the whole galaxy, but how do scientist know about our galaxy?

homework - Is this mammalian embryo blastocyst, gastrula or only phase between them?

The picture shows the formation of early blastocyst and late blastocyst.
The middle embryo has embryoblast.
My professor says that blastocyst in general has embryoblast and trophoblast.

Embryoblast is the inner cell mass but the thing has none of it.
The last embryo does not seem to have inner cell mass anymore.

Is the last embryo in the picture anymore blastocyst?

The given thing seems to be "the single layered blastocyst that will give rise to gastrula", Wikipedia Gastrulation. The given stage seems to last very short time. It probably should be called phase between blastocyst and gastrula so that the thing is not blastocyst and not gastrula.

What is the right name for the given thing in mammalians?

PCR amplification and error propagation

Your teacher is indeed correct.

In the first round you would get two identical molecules of the dsDNA.

In the second round you would get 3 identical molecules and one molecular with an A substituted for a G in one of the strands. ie.

No error (3 of the 4 molecules):

------G-------
------C-------

One mismatch (1 of the 4 molecules):

------A-------
------C-------

So there are a total of 8 strands of DNA after the second round and one of those strands has the mismatch. 1 / 8 = 0.125 = 12.5%

In round 3 you would have 8 dsDNA molecules and only one of those 8 dsDNA molecules would have the mismatch.

observation - What is in the brightest area of the night sky?

All quoted text in this answer is from image captions in the Wikipedia article on the Milky Way.

360-degree panorama view of the Milky Way (an assembled mosaic of
photographs) by ESO

This magnificent 360-degree panoramic image, covering the entire
southern and northern celestial sphere, reveals the cosmic landscape
that surrounds our tiny blue planet. This gorgeous starscape serves as
the first of three extremely high-resolution images featured in the
GigaGalaxy Zoom project, launched by ESO within the framework of the
International Year of Astronomy 2009 (IYA2009). The plane of our Milky
Way Galaxy, which we see edge-on from our perspective on Earth, cuts a
luminous swath across the image. The projection used in GigaGalaxy
Zoom place the viewer in front of our Galaxy with the Galactic Plane
running horizontally through the image — almost as if we were looking
at the Milky Way from the outside. From this vantage point, the
general components of our spiral galaxy come clearly into view,
including its disc, marbled with both dark and glowing nebulae, which
harbours bright, young stars, as well as the Galaxy’s central bulge
and its satellite galaxies. As filming extended over several months,
objects from the Solar System came and went through the star fields,
with bright planets such as Venus and Jupiter. For copyright reasons,
we cannot provide here the full 800-million-pixel original image,
which can be requested from Serge Brunier. The high resolution image
provided here contains 18 million pixels.

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Here is a schematic map of our POV in the Milky Way galaxy.

Observed (normal lines) and extrapolated (dotted lines) structure of
the spiral arms. The gray lines radiating from the Sun's position
(upper center) list the three-letter abbreviations of the
corresponding constellations.

A "God's view" map of Milky Way as seen from far Galactic North (in
Coma Berenices). The star-like lines center in a yellow dot
representing the position of Sun. The spokes of that "star" are marked
with constellation abbreviations, "Cas" for "Cassiopeia", etc. The
spiral arms are colored differently in order to highlight what
structure belongs to which arm. H II regions are marked as dots
colored in the same color as their spiral arm. They come in three
sizes, measured by the excitation parameter U: small - U > 200 pc cm-2
medium - 200 > U > 110 pc cm-2 large - 110 > U > 70 pc cm-2

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It turns out we are in an arm -- the Orion-Cygnus Arm. The much brighter part of the Milky Way from our POV is in the direction of the galactic center, but the actual nucleus around the supermassive black hole is obscured by dust. If it was visible, it would be quite bright. What we are seeing that is bright is mostly the pseudobulge, or galactic bar formation, in the middle of the galaxy. We are looking at the galactic bar almost end-on, so it resembles a sphere from our POV.