homework - Is secondary follicle or Graafian follicle arrested in the second metaphase of oogenesis?

Three follicular stages are recognised,
1) Primary/Preantral Follicles (with primary oocyte inside)
2) Secondary/Antral Follicles (with primary oocyte inside)
3) Pre Ovulatory Follicles (with secondary oocyte inside)

Pre ovulatory Follicles are formed ~36 hrs before ovulation at time of LH surge. This coincides with completion of Meiosis I and formation of the secondary oocyte. The secondary oocyte immediately enters Meosis II.

Appx. 3 hrs before ovulation, the Pre ovulatory Follicle (with the secondary oocyte inside) is arrested in the metaphase of Meiosis II and is extruded out of the ovary - a process called as Ovulation.

It comes to rest in the ampulla of the fallopian tube and here it is fertilised. As the sperm pronucleus is released into the cytoplasm, the Secondary Oocyte (now called the ovum) completes Meiosis II and releases the second polar body.

Hope this helps.

human biology - What is the eye muscle status when you stare at distant view through a glass wall?

In the situation you describe, the eye would be focused on the distant mountain. This would mean that the lens would be stretched and thin in order to minimize the focussing power of the eye. Therefore the ciliary muscles would be relaxed.

When you are looking out of the window, it is possible to make a conscious decision to focus on the window pane itself (thus adjusting the focus to be more powerful as the ciliary muscles contract), however then the distant object will be out of focus and uncomfortable to look at.

This is because the light rays reflecting from the mountain are barely affected by the pane of glass, hence its transparency.

If quasars are powered by black holes, why are they so bright?

A black hole, in deep space is basically black, and very hard to detect. But if a black hole is surrounded by material, that material will fall towards the black hole and enter into orbit about it. (Black holes don't suck, they gravitate)

The material may come from, for example another star, or in the case of the giant black holes at the centre of many galaxies, from the gas, dust and stars that are found in the cores of galaxies.

As objects orbit the black hole they will tend to collide with each other, releasing energy in the form of heat, and causing them to fall to lower orbits. This process tends to cause the gas orbiting a black hole to form into a disk, called an accretion disc. Pretty soon any larger objects will be broken apart, and the accretion disk will be composed of gas, and as it heats up, plasma.

Now as objects fall to lower orbits they speed up. And for a black hole, this speed up is extreme. The gas will be orbiting at speeds that approach the speed of light. This makes friction and collisions between the particles that are orbiting the black extreme as well. The accretion disk heats up, to immense temperatures.

Now something weird happens, and the physics of it is not really sorted out. Magnetic fields get tangled up in the hot matter and cause a portion of it to be ejected away from the black hole in a jet, perpendicular to the accretion disk. The speeds of the particles in the jet is close to the speed of light. Massive amounts of electromagnetic energy is also released along this jet.

Quasars are active galaxies that happen have their jets pointing towards us. The large amounts of gas need to supply a massive black hole with the energy to make a quasar were more common in the early universe, so many quasars are very distant and very old, but the youngest is only about 700 million light years distant, and there is every reason to suppose that quasars still exist today.

You don't need a binary black hole to make a quasar, but the merging of two black holes could also release massive energy, and may be a type of gamma ray burst, and should also release gravitation waves.

Very bright star in the east at northern hemisphere. What is it?

As other people have pointed out, it is hard to work out which star it is, without knowing your general location. However, after checking on Stellarium, there seem to be a couple of likely suspects:

• Sirius - the brightest star in the sky. I've seen it myself - and on a good, dark night, it can really stand out.


• Jupiter - the king of the planets is also rising at about the same time. It is brighter than any star in the sky, by a wide margin (though fainter than Venus), and it can really stand out.

Other than that, there aren't really that many objects rising in the East at the time you specify that could really stand out.

There are a couple of useful ways to tell the two apart:

• Sirius is a bright white object - perhaps with a subtle bluish tinge to it, whereas Jupiter has a slight yellow tint to it.


• Jupiter is currently rising in the North-East, and can get very high in the sky at the moment from the northern hemisphere, whereas Sirius rises in the South-East, and doesn't get that high (though that does depend on location).


• Sirius tends to twinkle, and 'flicker', as its light is disturbed by air currents, whereas Jupiter remains very steady - perhaps not twinkling at all.

As mentioned earlier, the best method is usually to use software like Stellarium, which will tell you exactly where everything is, and hopefully give you a definitive answer to which object it is.

fundamental astronomy - Calculation of hour angle

I need to determine Right Ascension and Declination from Azimuth and Altitude, working in C#. The problem is that the formula for calculating hour angle, for some reason, doesn't work. Here's the code:

        az = az * DEG_TO_RAD;
        alt = alt * DEG_TO_RAD;

        lati = latitude * DEG_TO_RAD;

        // Julian day
        JD = CalculateJDN(year, month, day, h, m, s);

        // Greenwich mean sidereal time
        GMST = CalculateGMST(JD);

        LST = GMST + longitude / 15;

        dec = Math.Asin((Math.Sin(lati) * Math.Sin(alt)) + (Math.Cos(lati) * Math.Cos(alt) * Math.Cos(az)));

        ha = Math.Atan2(Math.Sin(az), (Math.Cos(az) * Math.Sin(lati) + Math.Tan(alt) * Math.Cos(lati))); 

        ha = ha * RAD_TO_DEGREE / 15;
        dec = dec * RAD_TO_DEGREE;

        ra = LST - ha;

        // Input data for Mintaka (delta Ori):
        // az = 47.5, alt = -35.3 on 13:57 UTC, 1 Dec 2015
        // latitude = 43.897, longitude = 20.344
        // Required output: dec = -0.19, ra = 5.5
        // Given output: 
        // dec = -0.19, ra = 17.5, ha = 2.5

Az and alt are given in degrees, so they are first converted into radians. Functions for calculating Julian day number and GMST are correct, since I've already tested them. Formula for declination is good, but for some reasons formula for hour angle (ha) doesn't work. I don't know where's the error.

galactic dynamics - What happens to galaxies when they die?

Well, it would be useful to define what a 'dead' galaxy is. Probably the most simple method would be a galaxy that is no longer producing new stars. We might also consider a galaxy that no longer produces significant light in the visual spectrum, or perhaps EMR across the entire spectrum.

Generally, there's unlikely to be a firm line between living and dead, and not nearly as dramatic as larger stars. More akin to watching a camp fire burn itself out. Star formation is largely dependent available gases, but as more and more stars fuse those gases into heavier elements, there is less gas available for star formation. For your average sized galaxy, this will eventually result in running out of gas. Eventually the galaxy will dim and go dark, a process purported to begin at the center of the galaxy, where star formation is heaviest according to research based on Hubble images of giant galaxies. (Tacchella, et al.) The matter ought to (mostly) all still be there and still orbiting the (presumed) SMBH, but with no energy coming from fusion, it's going to be a dark, cold, and barren place. Sounds dead to me.

There are some complicating factors. It's believed that encounters with nearby galaxies can affect available gases. The gravity from a larger galaxy could potentially strip the gases from a smaller one, a fatal blow for the smaller galaxy. Fortunately, it won't suffer much as the death will come (relatively) quickly. This process has been deemed 'strangulation' by a study published in Nature several years months days ago. (Ping, et al.) Note that as the study indicates, the methods of death are proposed solutions - not conclusive understanding of the exact processes that result in a galaxy's death.

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S. Tacchella, C. M. Carollo, A. Renzini, N. M. Förster Schreiber, P. Lang, S. Wuyts, G. Cresci, A. Dekel, R. Genzel, S. J. Lilly, C. Mancini, S. Newman, M. Onodera, A. Shapley, L. Tacconi, J. Woo, and G. Zamorani. Evidence for Mature Bulges and an Inside-out Quenching Phase 3 Billion Years After the Big Bang
Science 17 April 2015: 348 (6232), 314-317. [DOI:10.1126/science.1261094]

Y. Peng, R. Maiolino & R. Cochrane. Strangulation as the primary mechanism for shutting down star formation in galaxies Nature 521, 192–195 14 May 2015 [DOI:10.1038/nature14439]

Andrea Cattaneo. Astrophysics: The slow death of red galaxies Nature 521, 164–165 14 May 2015 [DOI:10.1038/521164a]

genetics - Is sexual reproduction outside the same biological family possible? Has it ever occured successfully?

Are there any examples of two species taxonomically classified in different biological families that have successfully hybridized and produced viable offspring? If not, is there an example of where reproduction occured with non-viable offspring?

To be clear, I mean regular sexual reproduction that could occur in the natural world outside a lab. Even so, I'd be curious to know if it could even occur in a lab without direct genetic manipulation.

For example, grolar bears which are ursid hybrids between different species in the Ursus genus are known to exist. Also ursid hybrids between bear species in different genuses have been produced in captivity (sloth bear Melursus ursinus x Malayan sun bear Ursus malayanus and sloth bear x Asiatic black bear Ursus thibetanus). Would an extra-familial hybridisation be possible? Would this be more likely in the plant kingdom?

This question is inspired by a separate question on the Gardening SE which hints at a general lack of understanding of the genetic similarity required for cross-pollination in plants. It made me wonder whether there are any exceptions to the general assumption that extra-familial hybridisation is impossible.