Astronomy anyone quickly?

Question

How was the apparent magnitude scale developed?

What is the main fuel of a star?


what process makes a star hot?

Answer 1

A) Hipparcus, Ptolemy (and others) developed lists where the brightest stars were said to be "of the first magnitude". Then, the next brightest stars were marked "second" and so on until "sixth".

Magnitudes were ordinal numbers (integers only). There was no such thing as a "magnitude 3.5".

By the time astronomers developped instruments to measure intensity, the list had grown to hundreds. It was possible to measure the average intensity of all stars listed in a given rank, and then compare these averages among themselves.

The ratio was very close to 100 over 5 ranks.

So it was made that way.

Our eyes perceive luminosity as a logarithmic function (same as our ears with sound frequency), so each rank was made so that the logarithm of the intensity grows by 0.4 (in base 10) for each step of 1 magnitude. Five steps of 0.4 = 2 and the antilog of 2 is 100.

The antilog of 0.4 is 2.511886

Reference stars were selected to pin down "magnitude 0". This was selected so that most of the stars identified in the old catalogs would retain the same ranking (in general, a third magnitude star would still have a value near 3.0).

One scale had Polaris pegged at 2.0 (then it was found that Polaris is a variable star). Vega was also selected as a star of 0.0 because it was thought to be a non-rotating star (no doppler shift from the edges). Turns out that Vega is a rapidly-rotating star seen almost pole-on. In fact, it is turning on itself so fast that its equatorial region is lifted sufficiently for it to be darker than it should be for its mass.

Still, there are reference stars and the scale is sufficiently pegged down.

The original ranking is how we ended up with a scale that runs backward (0 = bright, 3 = less bright, 6 = barely visible, etc. We also have stars brighter than 0: they get a negative number (Sirius has an apparent magnitude of -1.44)

B) When the cloud of gas and dust (mostly hydrogen) has collapsed onto itself, the centre reaches temperatures and pressures such that fusion begins (millions of degrees). The energy provided by fusion slows down the collapse. At the collapse continues, more pressure causes more fusion, causing more heat, causing more pressure to counter collapse.

C) At some point there is a balance. The more massive a star, the hotter it needs to be to be balanced (pressure equals collapse), the more fusion is needed to keep the temperature, the more fuel is consumed per unit of time.

Each fusion event generates a very high energy photon (and neutrinos). Because of the high pressure and temperature, the photons are almost immediately absorbed by something which gains energy then releases new photons, etc...

The photons distribute the energy among all the particles up to a certain distance from the centre. At a certain point, the pressure is still high but the temperature has lowered enough for matter to behave like a liquid. The heat is transported by convection cells to the surface.

The surface of the star gets all that heat and must radiate it away. The surface acts like a blackbody that is heated enough to generate photons (like a stove element that becomes hot enough to glow red).

Our Sun's surface is just below 6000 C (almost 11,000 F). And this temperature, by itself, is responsible for the light we get from the Sun.

The photons that are produced by the central fusion never see the light of day (I know, awful pun -- difficult to resist).

Answer 2

Magnitudes are measured by a logarithmic scale where a first magnitude star is exactly 100 times brighter than a sixth magnitude star. That makes a star one magnitude brighter than another star about 2.51 times brighter.

Answer 3

The main fuel of the star is hydrogen. When it is in the low pressure in the star, it is too much that hydrogen atoms collide with each other and releases a lot of energy and heat. Sometimes it becomes HELIUM

NUCLEAR FUSION MAKES THE STAR HOOOOOOOOT

Answer 4

A.
B. Hydrogen
C. Fusion