UFO'S of UAP'S, ASTRONOMIE, RUIMTEVAART, ARCHEOLOGIE, OUDHEIDKUNDE, SF-SNUFJES EN ANDERE ESOTERISCHE WETENSCHAPPEN

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While much of the cosmos remains mysterious and unexplored, we know this much is true: space is big. Very big. To quantify the vastness of the cosmos, astronomers often refer to things being a certain number of light-years away. What does that really mean?

Though seemingly contrary to how it sounds, a "light-year" is a measure of distance, rather than time. A light-year is the distance light travels in a year. Specifically, the International Astronomical Union defines a light-year as the distance light travels in 365.25 days.

In a similar vein, you could describe 60 miles as a car-hour (the distance a car travels in an hour on a highway). In fact, we often tell people distances in terms of time – "I'm 10 minutes away," for instance. The term "light-year" was invented because, simply put, the equivalent distances in miles, meters or kilometers were huge. [The Biggest Unsolved Mysteries in Physics]

How huge? Light moves at 186,282 miles per second, or 299,792.5 kilometers per second. That's 670.6 million miles an hour. The distance to the nearest star is 4.3 light-years, or 25.3 trillion miles (40.7 trillion km).

The first mention of light-years dates back to 1838 and a German scientist named Friedrich Bessel. He measured the distance to a star called 61 Cygni, and got a distance of 660,000 times the Earth's orbital radius. He noted that light would take about 10 years to get there, but he didn't like the term "light-year." (One reason was that at that time, it wasn't clear that light's speed was a fundamental constant of nature). In 1851, the term made a first appearance in Germany, in an astronomical publication known as Lichtjare. Later, astronomers adopted it and "light-years" are now a popular unit of measurement even in the scientific literature.

The light-year competes with the parsec, which stands for parallax-second, and is equal to 3.26 light-years. A parallax-second is the number of arcseconds (1/3600th of a degree) that a star's apparent position shifts when measuring its distance. British astrophysicist Arthur Eddington, a prominent scientist in the early 20th century, preferred the parsec, calling the light-year "inconvenient." His was a losing battle, however.

Light-years can be divided into light-days, light-hours or even light-seconds, though those units are used less often. The sun is 8 light-minutes away, which means it takes light from the sun 8 minutes to reach Earth. [Quiz: How Well Do You Know Our Solar System?]

All this depends on knowing the speed of light, and that turns out to be hard to measure because it goes so fast. Galileo attempted it in 1638, and he described an experiment in which one person covers a lantern while another on a tower some distance away tries to time when the light gets there. The experiment failed, and Galileo could only answer that however fast light was, neither human reflexes nor the clocks at the time were speedy enough to catch it. (He did come up with an estimate of at least 10 times the speed of sound, but that was very much a guess.)

Danish astronomer Ole Rømer was able to make an estimate in 1676, using the timing of eclipses of Jupiter's moon Io. Later, in 1729, James Bradley used a phenomenon called stellar aberration, in which the apparent positions of stars in the sky seem to change slightly depending on the movement of the Earth, to get a closer estimate of light's velocity. Scientists kept refining these estimates, and by the 1860s, Scottish physicist James Clerk Maxwell showed that electromagnetic waves travel at a certain speed in a vacuum. That speed is a constant, and at the time, most physicists thought of light as a pure wave. (We know now that it isn't – it can be a particle, too).

Finally, in 1905, Albert Einstein's theory of special relativity posited that light always travels at the same speed no matter where it is observed from. This was a big step because suddenly, the speed of light became one of the constants of the universe – and thus, more useful for measuring distances.

Original article on Live Science.

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Live Mice Are Bred from Artificially Developed Egg — **Mice born from parthenogenotes, along with their offspring.**
**Credit: Toru Suzuki et al., 2016/Nature Communications**

For the first time, live baby mice have been successfully produced by injecting sperm into a modified, inactive mouse embryo rather than from a fertilized egg cell, according to scientists.

Mammalian eggs that are not fertilized can be "tricked" into starting the development process toward becoming an embryo, previous research has shown. These unfertilized, slightly developed embryos are called parthenogenotes, but they die soon after they are created, due to the lack of sperm input, which triggers developmental processes.

In the new research, the scientists took these inactive embryos and injected sperm directly into them, which resulted in the birth of healthy baby mice with a success rate of up to 24 percent.

The experiment produced the first ever full-term live mice born fromparthenogenotes that were injected with sperm, senior author of the study Tony Perry, a molecular embryologist at the University of Bath in England, said in a statement. [Future of Fertility Treatment: 7 Ways Baby Making Could Change]

"It had been thought that only an egg cell was capable of reprogramming sperm to allow embryonic development to take place," Perry said. "Our work challenges the dogma, held since early embryologists first observed mammalian eggs around 1827 and observed fertilization 50 years later, that only an egg cell fertilized with a sperm cell can result in a live mammalian birth."

In order to keep the parthenogenotes from perishing as they normally would, the researchers exposed them to a salt compound calledstrontium chloride (SrCl2). Previous research had shown that this salt encourages parthenogenetic embryos to begin normal cell division, despite not having been fertilized. The chemically modified parthenogenotes were then injected with the sperm and implanted intosurrogate mothers.

The research upended the notion that mammalian sperm cells could only transform into mature sperm cells when they were within an egg — it was thought that only the egg provided the environment for division to begin, and a complex organism to develop. But the new experiment has shown that a parthenogenote can serve the same function as an egg — under the right conditions.

The mice born from the experiment were seemingly healthy, the researchers said. Their life expectancies were similar to those of control mice that were bred traditionally, and they were able to reproduce.

However, the mice born from the parthenogenote experiment had different epigenetic signatures in their DNA, compared to mice born from traditional fertilization. Epigenetic signatures are chemical modifications that are made to a DNA code, outside of the DNA "letters" themselves. The researchers suggest that this means that different epigenetic pathways can lead to the same developmental destination.

As the research continues, reproduction techniques that use parthenogenotes and sperm could be applied to conservation efforts in the breeding of endangered animals, and help treat infertility and other reproductive issues, the researchers said.

"This is an exciting piece of research which may help us to understand more about how human life begins and what controls the viability of embryos, mechanisms which may be important in fertility," Paul Colville-Nash, from the Medical Research Council (MRC), which funded the work, said in the statement. "It may one day even have implications for how we treat infertility, though that's probably still a long way off."

The study was published online Tuesday (Sept. 13) in the journal Nature Communications.

Original article on Live Science.