Stellar Explosions Can Create The Awesome Beauty Of Light Echoes
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In 2002, the Hubble Space telescope watched as the star V838 Monocerotis exploded in a fiery detonation 600,000 times brighter than our sun. Over four years, the telescope kept watching, and it captured something amazing: instead of gradually petering out, the explosion periodically brightened in what's known as a "light echo."
A Thorne-Żytkow Object Is A Star Within A Star
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There's some weird stuff in the universe. Among all the binary systems, stellar voids, and bubble-shaped nebulae that we know exist, there are a great many we only think exist. One of those is a Thorne-Żytkow object (TZO), or a star that contains another star. At least, that was the case until astronomers finally detected their first TZO in 2014.
The Milky Way's Center Contains A Star Desert
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There's a place in our galaxy where no new stars are born. In a paper for the Monthly Notices of the Royal Astronomical Society, University of Tokyo researchers reported that a massive portion of the Milky Way's Extreme Inner Disk contains almost zero young stars, meaning that the area hasn't produced new stars for potentially hundreds of millions of years. The researchers discovered this fact when they were searching for Cepheids, a type of super-young star that's easy to detect based on its predictable pulsation pattern. Because that pattern makes it easy for astronomers to estimate their age and distance, Cepheids are a great way for us to learn more about the formation of our galaxy. When they looked for Cepheids in the inner Milky Way, however, they came up virtually empty. An expanse extending 8,000 light years from the galaxy's center is essentially a "stellar void," containing virtually no Cepheids at all. This new discovery about our stellar home is one more step in learning all there is about the Milky Way. Explore what we do know about our galaxy in the videos below.
How Important is SPF for Sun Protection?
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When it comes to sunscreen, a higher SPF should protect against more UV rays than a lower one. And it does, but not by much. SPF 15 sunscreen blocks 93% of UVB radiation. SPF 30 blocks around 97%, and SPF 50 blocks 98%. "As you get higher and higher, it's not really a practical difference," American Academy of Dermatology president Dr. David M. Pariser told the New York Times. Here's why: companies calculate SPF by comparing the time it takes a person to burn unprotected with the time it takes for them to burn wearing sunscreen. Therefore, if you burn after 20 minutes with no sunscreen, you should theoretically be able to last for 15 times longer -- a whopping five hours -- with SPF 15. But sunscreen itself doesn't usually last that long. Sweat, friction, and simple quirks of product formulation can make it wear off, which is why dermatologists recommend reapplying every two hours. That means it doesn't really matter whether you get the SPF 30 or the SPF 100, since the formula will probably wear off before the difference in protection becomes important. What is important is applying sunscreen properly: for a full-body application, you should use an ounce of sunscreen, or roughly the volume of a shot glass. And because SPF is only a measure of UVB protection, you should look for a full-spectrum formula that protects againsts both aging-related UVA and sunburn-related UVB rays.
from Bytesize Science
Key Facts to Know
Sunscreens protect skin from UV light, which can damage skin cells and cause sunburn, moles, freckles, and wrinkles. 0:48
UV-B light is the primary cause of sunburn. UV-A penetrates more deeply, causing more long-term damage like wrinkles and age spots. Both can cause skin cancer. 1:02
SPF 15 protects the skin from 93% of UVB rays. SPF 30 protects it from 97%. 2:38
Stars Have Atmospheres, Too!
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Like planets, stars have atmospheres that consist of gases. In fact, any body in space with enough mass to generate the necessary gravitational pull will have an atmosphere. The atmosphere of our sun has three layers: the photosophere, the chromosphere, and the corona. The photosphere is where solar flares happen, and where the sun's energy becomes light. The chromosphere cannot typically be seen against the photosphere's brightness in the background, but you can catch a glimpse of it during a total solar eclipse, when it appears as a red rim around the sun. The corona is likewise only visible during a total solar eclipse, and looks like pearly plumes and loops of gas.
from SciShow Space
Key Facts to Know
If you approached the sun in a regulation EVA spacesuit, other types of radiation would kill you before the heat would. 0:21
Most spacesuits are designed to withstand temperatures up to about 400 Kelvin. 1:49
A spaceship approaching the sun could withstand higher temperatures than a person in a spacesuit, but it would also absorb more heat. 2:26