Answer:
Astigmatism is a problem of how the eye focuses light typically caused by a defect in the lens, resulting in distorted images. Astigmatism is not an eye disease or health problem. While it can cause blurred vision, eye strain, and headaches, particularly after prolonged reading, it does not cause blindness.
Astigmatism can be corrected with glasses, contact lenses, or refractive surgery (i.e. laser eye surgery), although treatment may not be necessary if the symptoms are mild. Glasses and contact lenses both compensate for the irregular shape of the cornea and help to focus light properly into the back of the eye
The epiglottis is the flap in the throat that prevents food from entering the trachea
Answer:
If two similar looking species are able to produce fertile and viable offspring, then they belong to the same species.
Explanation:
According to the biological species concept , organisms are said to be of same species if they are able to interbreed and produce fertile and viable offspring.
In case if two species are closely related on the basis of external features, then they must be allowed to mate. The offspring produced in the first generation mating must be allowed to mate again. If in the second generation offspring are produced, then it shall prove that the two similar looking organisms are able to produce viable and fertile offspring thereby establishing the fact that they belong to same species.
The sun provides a handy benchmark for describing other stars. The mass of this solar system's sun gives us a unit for measuring other stars' masses. Similarly, the sun's luminosity and surface temperature define the center of the Hertzsprung-Russell Diagram (H-R Diagram). Plotting a star on this chart reliably predicts other qualities of the star, such as mass and age. The main sequence phase of a star's life cycle is that time during which hydrogen fusion takes place in its core. But in terms of the H-R Diagram, "main sequence" also refers to a roughly diagonal, slightly S-curved line stretching between the upper-left and lower-right corners on which main sequence stars chart. They maintain a predictable relationship between luminosity and temperature: the brighter, the hotter. Both of these traits increase with a star's mass; a star indicated closer to the upper-left corner will be "heavier" than our sun, while lower-right main sequence stars will be "lighter."
Red Giants
Should astronomers plot a newly discovered star in the upper-right corner of the H-R Diagram, being both bright yet cool, they'll immediately know what phase of its life cycle the star is enduring. A red giant's core, hot enough to fuse helium and even heavier elements, has pushed its shell layers so far out that they can cool into the red spectrum. They owe their great luminosity not to their temperature, but to their size: bigger stars radiate more light energy.