The site in-the-sky.org has a wide variety of functions and options. In Planetarium mode, I chose a random city at about 24N and in the middle, which helps to get the correct UTC + 05:30 India Time Zone, and then just put in the time and date and turned on alt/az grid.
So it is likely to have been Jupiter, as you suspect. Below are two screen shots - 20:00 and 23:00 local time, with Jupiter climbing from 41 to about 73 degrees above the horizon.
Earth gets its radiation input primarily from Sun, then from reflected sunlight from Moon, and stars. Among these, what is the share of stars (or sources outside solar system) to this total radiation input of Earth. Is it negligible compared to solar radiation? (I am referring to top-of-atmosphere situation.)
It depends how you define locomotion.
If you take it to mean moving from one place to another, then yes, almost all plants do this at some stage during their life cycle. Primarily seeds and pollen move around, and generally they do so by harnessing either natural forces like wind and rain, or by manipulating animals to do the leg-work, e.g.:
If you take it to mean moving around under ones own propulsion, then yes, some plants do this. The example that springs to mind is the gametophyte generation of ferns:
The prothallus (i.e. the gametophyte) has rhizoids on the underside and uses them to slide around and find some space in which to start the next generation. I have seen this happen when fern spores are germinated on agar - when they reach the tiny prothallus stage, they start sliding around to avoid overlapping with one another. I can't find any references for this, but I'll keep looking.
Another example of self-directed locomotion in plants is the motile sperm of bryophytes. The male sex cells have flagella, which they use to propel themselves through water to the female sex cells (reviewed by Renzaglia & Garbary 2001).
The answer is that in a pre-supernova star, most of its mass is still in the form of hydrogen and helium. It is only the central core where the primordial H and He has fused to heavier elements.
This picture of onion layers is typically what you see in elementary text books. It is completely misleading in a quantitative sense. It schematically represents what's at the centre of the pre-supernova star, but in terms of the mass that is in each shell (it is obviously a 3d object) you get completely the wrong idea, because this diagram is only about 1 Earth diameter across, compared with the actual stellar radius of something like the distance between the Earth and the Sun!
Here is a more sophisticated plot taken from a paper by Fuller et al. (2015). It shows time until the supernova along the x-axis and the y-axis represents a radial assay of the chemical composition from the centre of the star to the outside. The initial total stellar mass is $12M_{odot}$. As you move leftwards towards the supernova explosion, notice how what is at the core changes - from being H dominated, to He dominated, to C/O dominated then Si and finally Fe (actually iron-peak elements). Note how much mass is contained within these core region for each stage of nuclear burning. The edge of the "helium core" encloses the central $4M_{odot}$ of the star. The subsequent heavier element cores inside the onion ring structure enclose significantly less mass, until the iron core is around $1.3M_{odot}$ just prior to the explosion. Blue shading indicates regions that are thoroughly mixed and homogenised by convection.
After the explosion, the neutron star that is produced will also have a mass of around $1.3-1.4M_{odot}$. In other words most of the rest of the star (about $10M_{odot}$ just prior to the explosion) gets blown out in the supernova. But of the $8.6M_{odot}$ that makes into the interstellar medium, well over half is still in the form of hydrogen and helium; the minority will be carbon, oxygen, neon, silicon, iron etc., and only a very small fraction of that will have been transformed (by the r-process) into elements heavier than iron and nickel.
Thus although the material injected back into the interstellar medium is enriched with heavier elements, there is still plenty of hydrogen to start a new generation of stars. It is also the case that star formation is an inefficient process, so the material from which the supernova progenitor formed will still mostly be around in the interstellar medium. The picture you should have is of a gradual enrichment with heavy elements, especially as the interstellar medium gets churned up and mixed through a variety of processes (including supernova explosions!).
EDIT: Here is an even more awesome picture. The lower plot shows the relative mass fraction of each element as a function of enclosed mass as you work your way out from a 15 solar mass star (it has shed 2 solar masses during its evolution). The really awesome thing is that it is animated, so it shows you the first few moments after the core-collapse and how things start to change. Note that the outer $5M_{odot}$ of the envelope is about half H and half He by mass prior to the core collapse. Lots of He and then O in the layers below that. The upper plot show how the density temperature and outward velocity are behaving. The image is from the website of Woosley and Heger (2007), a canonical work on the subject.
Hmm. I can't upload the animated gif. Here it is; well worth a look.
Exercise, such as running, increases muscle activity. This increases the energy demand of these tissues, which increases the rate of cellular respiration. Respiration releases heat as a by-product, therefore the body is hotter during and after exercise.
Sweating is a homoeostatic mechanism to keep core body temperature constant. It is a response to lower the body temperature. When the body becomes too hot, sweat is released onto the surface of the skin. The water from the sweat then takes some of the excess heat energy from the body and uses it to evaporate. Because water has a relatively large specific heat capacity a lot of heat can be carried away by this method.
The structure (mass versus radius and density profile) is influenced by its rotation rate, but not by as much as you might think.
Even in Newtonian physics you can think of a mass element $m$ at the surface of a star of mass $M$ and radius $R$, rotating with angular velocity $omega$.
A condition for stability would be that the surface gravity is strong enough to provide the centripetal acceleration of the test mass.
$$ frac{GMm}{R^2} > m R omega^2$$
If this is not satisfied then the object might break up (it is more complicated than this because the object will not stay spherical and the radius at the equator will increase etc., but these are small numerical factors).
Thus
$$ omega < left(frac{GM}{R^3}right)^{1/2}$$
or in terms of rotation period $P = 2pi/omega$ and so
$$ P > 2pi left(frac{GM}{R^3}right)^{-1/2},$$
is the condition for stability.
For a typical $1.4M_{odot}$ neutron star with radius 10 km, then $P>0.46$ milli-seconds.
Happily, this is easily satisfied for all observed neutron stars - they can spin extremely fast because of their enormous surface gravities and all are well below the instability limit. I believe the fastest known rotating pulsar has a period of 1.4 milli-seconds.
You also ask how pusars can attain these speeds. There are two classes of explanation for the two classes of pulsars.
Most pulsars are thought (at least initially) to be the product of a core-collapse supernova. The core collapses from something a little smaller than the radius of the Earth, to about 10km radius in a fraction of a second. Conservation of angular momentum demands that the rotation rate increases as the inverse of the radius squared. i.e. The spin rate increases by factors of a million or so.
Pulsars spin down with age because they turn their rotational kinetic energy into magnetic dipole radiation. However, the fastest rotating pulsars - the "milli-second pulsars" are "born again", by accreting material from a binary companion. The accreted material has angular momentum and the accretion of this angular momentum is able to spin the neutron star up to very high rates because it has a relatively (for a stellar-mass object) small moment of inertia.
In a white dwarf, the dense matter is not in its lowest energy configuration. Energy can still be extracted from the white dwarf material by fusion, provided it can be ignited.
What exothermic nuclear reactions would there be that could take place in a neutron star? The bulk of the material is in the form of neutrons with a small number of protons and electrons. At these densities, that is the most stable equilibrium composition.
If a neutron star gains mass in a gradual way, then the most likely course of events will be that its radius will decrease (that is what happens in objects supported by degenerate matter) until it reaches a General Relativistic instability where its collapse to a black hole is inevitable (when $R$ is somewhere between 1.25 and 2 times the Schwarzschild radius). It is possible that neutrons may transform before that into additional hadronic degrees of freedom or into quark matter, but these are endothermic processes that suck kinetic energy out of the neutron gas and only hasten the collapse.
The branch of science you are looking for is taxonomy, that is the science of identifying and naming species, and arranging them into a classification.
Modern taxonomy was born from the studies of the Swedish zoologist Carl Linnæus (1707-1778), who first introduced, in his books Systema Naturae (Systems of Nature) and Species Plantarum (Plants Species) the now common binomial nomenclature where each different species is given a Latin name composed by two parts: one identifying the genus and one identifying the species.
For instance, various species of mice are in the genus Mus: the common house mouse is Mus musculus, but in the West Mediterranean you have another type of mouse, called Mus spretus.
Although this rigorous type of classification is quite recent, taxonomy existed much earlier.
Shennong, Emperor of China somewhere around 4000BC apparently tasted hundred of plants to test their curative properties. He wrote his observations in a book called the Shennong Ben Cao Jing.
On a similar note the Ebers Papyrus, dating ~1550 BC contains description of the properties of many plants.
To more "recent" times, around 300BC Aristotle was the first who actually classified animals (e.g. vertebrates and invertebrates) and his student Theophrastus wrote a classification of plants in his Historia Plantarum (Hystory of the Plants).
Some 400 years later Plinius in the Naturalis Historia (Natural History) enumerated many plants and animals and gave some of the first binomial names to certain species.
As to the point of how did they distinguish species: well, with their eyes and ears, of course!
You can distinguish a mouse from a vole because it is skinnier and has a longer tail.
Even more similar species can be easily distinguished without needing special equipment.
A good birdwatcher can distinguish a chiffchaff from a willow warbler by listening to their songs, looking at how they behave how they fly, the subtly different tones of their feathers etc.
We can do that now, without any special equipment, so they could before the Renaissance!
I don't think primer dimers are your primary concern here. Usually in my experiences, I get primer dimers all the time, even if the reaction works and I get my bands of interest.
Maybe you ought to troubleshoot other aspects of your PCR that might account for why your reaction isn't working. Have you tried using a positive control with your primers? You may try varying the parameters of your PCR as well. Remember, standard Tms are calculated according to a 50mM salt concentration: is that what you're using?
Generally, if the annealing temperature is above the predicted Tms of your primers, this represents a more restrictive and selective amplification of your target. You usually use a high annealing temperature if you're seeing lots of non-specific products. Since you're seeing no products at all, consider lowering the Tm to that of your primers (50º).
If you start seeing non-specific products at that Tm, I'd do what we call a "Touchdown" PCR -- that is, you start the reaction at a higher annealing temperature, and as each cycle progresses, it "touches down" to a lower annealing temperature. The principle behind this is that it starts it off at a restrictive temperature -- so your yield is very low initially, but then by gradually decreasing the "restrictiveness" of the reaction, your yield will improve. This will still prevent non-specific amplification b/c the less restrictive amplification will be on the fragments already amplified from the restrictive condition. Remember, biology is not exact science. Just because something says the Tm is such and such does not mean it's absolute and doesn't give you some margin of error. For example, we exploit that margin of error to optimize our experiments in the example I outlined above.
Anyways, (might have went on a tangent a little bit) you also have to consider how you designed your primers. Primers wil high self-complementarity will self-anneal at higher Tms.
Humans, like all vertebrates, belong in subregnum bilateria, a broad class of animals whose characteristic trait is having a bilaterally symmetric body plan at least in some of their life stages.
The common ancestor of all bilaterians was presumably something like a small marine worm. For a primitive animal living in water, an obvious advantage of bilateral symmetry is that it makes directed swimming easier. If the animal were completely asymmetric, it would have to continually exert active control over its heading to be able to swim straight. On the other hand, an even more symmetrical animal (such as one with 90° rotational symmetry) might have trouble controlling its vertical and lateral heading separately, which could be a problem in aquatic habitats where staying at a certain depth is often useful.
(Indeed, in many ways these reasons are the same as why pretty much all aircraft are bilaterally symmetric: in the absence of active steering, we want them to fly straight and level. That requires at least rough left–right symmetry and generally also some degree of top–down symmetry, although some breaking of the latter is usually needed both for landing and to account for the effects of gravity on flight dynamics. We could build completely asymmetric aircraft if we wanted, they just would be harder to fly.)
As for why this ancestral bilateral symmetry has survived so well throughout the course of evolution, that's presumably both because it's so deeply embedded in the genes that control our ontogeny, but also because the basic reasons why such symmetry is useful still remain, even though our size, shape, habitat and locomotion are very different from those of the first "urbilaterian". Even though we mostly move by walking instead of swimming, it's still useful for us to be able to walk straight without having to pay constant attention to it. Furthermore, once we've first learned to walk (or crawl) straight, it's useful that we can also learn to run, swim and jump (and ride a bike or drive a car) straight without having to always re-learn the exact amount of control needed to maintain a given heading with each of these modes of locomotion.
Ps. To answer your actual question, I'd guess, like Rory M, that the two halves of a human body probably won't weigh exactly the same, both due to the asymmetrical distribution of the internal organs and also due to uneven muscle development.
However, the difference is quite small compared to the total mass of the human body, so that the center of mass is presumably still quite close to the body's centerline. As I noted above, any significant deviation from that would cause issues with gait and balance. Although such issues can certainly be adapted to and overcome with active control — after all, even people who've lost a whole leg manage to get around one way or another — they're presumably still significant enough to be selected against over evolutionary timescales, which is why our body shape remains so nearly symmetrical.
I would guess that the eye muscle relaxes when the eye is closed. After having the eyes closed, just in the moment after opening them, it seems that the focus is in the distance. It takes a fraction of a second before you can read some text on your computer screen for example . This focusing-duration seems to be shorter when looking into the distance after opening the eyes.
Another effect is when you look at an object in short range for quite a moment and then close your eyes. You can feel the relaxation.
I want to calculate the distance between two quasars of which I know the angular position and the red shift. Let $Q_1=(alpha_1,delta_1, z_1)$ and $Q_2=(alpha 2,delta 2, z_2)$ and suppose $z_2 > z_1$.
I know how to find the angular separation $theta$ between them by means of the angular coordinates. But how to find the comoving distance (at epoch $z=0$) from them ? I know how to find the comoving distance from the Earth of the two quasars, can we find the distance between them using these two distances?
A related question is to find the redshift of $Q_2$ as seen by $Q_1$ at the epoch when $Q_1$ received the light emitted from $Q_2$ .
There is some standard method to solve this problem ?
This is a clear example of an astrophysical jet, in this case, most likely a relativistic jet. In short, an accretion disk forms around a black hole (supermassive or otherwise). Matter is pulled towards the black hole and further energized, before being accelerated into a jet emanating from the black hole's poles. Two different mechanisms have been proposed for the formation of jets:
The hotspot is, to me, much more interesting. It reminds me of structures seen around young stars: bipolar outflows (streams of gas that can form shock waves) and Herbig-Haro objects (the results of shock waves from relativistic jets. Obviously, the mechanisms are different, so no clear analogy can be drawn. But what is interesting about bipolar outflows and Herbig-Haro objects is that the shock waves produced therein result from collisions with the interstellar medium.
If a similar mechanism were to cause the shock waves by the hotspot, then we could conclude that the jets have hit the intergalactic medium. But I don't think this is necessarily the case, in part because of just how long these jets are prior to the formation of the hotspot. One would think that if the hotspot and shock waves are because of collisions with the intergalactic medium, the jets would be much shorter, because they would likely have reached higher density regions of it sooner. So that's why I find it interesting, and why I can't give you a good reason as to why the hotspot formed where it did, or the precise reason for it being there at all.
Do the 46 human chromosomes form a single unbroken DNA helix? Or is it rather that a human's genome consists of 46 disconnected helices?
If it is the former, does the common numbering scheme for the chromosomes have any correlation to their actual ordering in the one large strand?
If is the latter, is there a convention on how the chromosomes are ordered in genomic datasets? Also, is there a clear understanding of how sister chromosomes "find" each other in Meiosis I?
Generally, during periods when Mitosis/Meiosis are not occurring, what's a good physical picture for how the chromosomes are physically arranged (e.g. a bowl of 46 spaghetti noodles, or maybe the sister chromosomes always stay close together, etc)
thanks!
NASA doesn't have its own asteroid tracking program. They are rather coordinating activities and provide funding for asteroid research and discovery programs.
The most successful dedicated asteroid discovery programs at the moment are Pan-STARRS (http://pan-starrs.ifa.hawaii.edu/public/) and the Catalina Sky Survey (http://www.lpl.arizona.edu/css/); see http://neo.jpl.nasa.gov/stats/ for some discovery statistics. Both these programs, as well as many others, run telescope that survey the night sky for yet unknown asteroids. On average, both programs together find 4 new near-Earth asteroids (and many others) per night.
The position of stars change very slowly for a couple of reasons, but not due to an expanding universe.
Galaxies distant from our own, are all moving away from our galaxy at a rate proportional to their distance. The equation is simple:
$$mathrm{speed}=H_0 times mathrm{distance}$$
and $H_0$ is a constant of proportionality, with a value of about 70 km/s per kiloparsec. Since the galaxies are moving away, they don't change their position in the sky at all.
(The nearest galaxies are exceptions to this rule, they may be moving towards us)
Stars in our galaxy are also moving. They have their own proper motion, but the motions of the stars relative to our own are essentially random. You can look up the proper motion of stars on the SIMBAD database.
Stars also appear to wobble due to the annual rotation of the Earth about the Sun and our consequentially changing perspective. The amount of wobble is in inverse proportion to their distance (the nearest stars appear to wobble most)
Some good answers, I'm going to give kind of summary, cause you touched on a few points.
Why does gravity increase in star formation
Gravitation is a product of a few forces. Mass, density and, not to be ignored, rotation speed.
It's not actually the fusion process that keeps the sun from contracting, at least, not directly. It's heat that keeps the star expanded. That's the balancing act. High temperature wants to expand, gravity wants to contract.
The fusion process is actually pretty slow, which is why stars like our sun have a main sequence of about 10 billion years, and a lot of the heat that a star starts out with is from the heat of formation. Potential energy gets converted to heat due to the coalescing and condensing of all that matter so stars start out hot, even before fusion begins.
In fact, a star in formation can be many times brighter than the star is during it's main sequence due to the high heat of formation. Here's an article that says the forming sun was 200 times brighter than it is now.
Young proto-stars, as a result of conservation of angular momentum, tend to rotate very fast and that fast rotation can create a bulge and increases ejection of matter. The formation process is pretty chaotic compared to the main sequence stage. Lots of ejected matter, much bigger solar storms, lots of lheat from formation, etc.
Once the main sequence stage is underway and rotation is slowed down, then there's more of a balance between heat and gravity mentioned above. The fusion process continues to add heat to the core of star which the star, convects or conduct heat away from the core into the outer layers and then, radiates from it's surface, but during the main sequence, in general, the core of the star gradually heats up and in most cases, the energy added from fusion isn't nearly strong enough to blow apart the star, unless the star is enormously large like over 150 or 200 solar masses, then the star doesn't really work without blowing off a bunch of matter. See: here.
I get that the fusion of hydrogen atoms releases energy... fine...
How does gravity keep it together if the mass is lessening as a result
of fusion( mass being converted into energy from fusion) while gravity
is weakening( as mass lessens )?
As others have said, mass loss by solar wind is a bigger factor especially for young and smaller stars, but there's a few factors at play. The short answer to this question is that the mass loss, at least by fusion, is quite very compared to the total mass of the star. Another factor, as hydrogen becomes helium, the core of the star becomes denser and greater density tends to be smaller and that increases gravity, but there are competing factors. The inner core grows denser as it becomes more hydrogen rich and the fusion tends to expand outwards on the outside of the helium core, so a star like our sun gets a denser inner core over time, but the layers around the core can grow hotter and larger, even as they lose mass.
Wouldn't the radiation overpower the force of gravity and tear the
star apart?
As mentioned above, this happens if you have 150 or 200 solar masses. lower mass stars, the fusion isn't nearly powerful enough to blow the star apart. Stars and white dwarfs blow apart when they go supernova, but that's different than the main sequence fusion process.
Our sun will blow off some of it's matter when it has it's helium flash, so there are examples of what you're describing happening, but not during the main sequence for stars like our sun when material is expelled primarily by magnetic storms causing coronal mass ejections. Fusion is, generally speaking, more like a slow burn, than a big explosion when it's up against the enormous gravitational binding energy of a star.
Every day, babies are born and people grow, which makes their respective masses greater. However, this change in mass (should) come out of the food that they consume - it is used as energy and thus converted into this growth. Likewise, building new structures is just a redistribution of mass already on Earth.
Thus, the only way I can see the actual mass of the Earth changing is by meteors that have landed here (increase in mass) and things that leave Earth such as space shuttles and rockets which would be a decrease in mass.
But have I missed anything out? If no meteors crashed into Earth, and we had not yet figured out how to make machines that could fly, would the mass of the Earth remain constant? Or is it somehow loosing or gaining mass? Am I wrong in assuming that the growth of animals doesn't affect the mass?
Thanks, Toastrackenigma.
EDIT: Mass includes atmosphere :)
