Why is the Sky Blue?

Have you ever wondered why the sky is blue? Or why sunsets exhibit such pretty colors? Well the answer is pretty simple, and of course involves astronomy!

  

The Sun emits what we perceive as white light. If you send a beam of white light through a prism, you will see that it breaks up into all the colors of the rainbow. Each color of light has a different wavelength and therefore a different energy.

Gas molecules in the atmosphere have the ability to absorb and/or scatter light. And based on the type of gas molecule, it likes to interact with only certain colors of light. The atmosphere is made mostly of nitrogen and oxygen. These two molecules tend to let all colors of light pass by unharmed, except for blue light. Blue light has just the right energy to be absorbed and scattered by the gas. Therefore we have lots of blue light bouncing around in the atmosphere, making the sky appear blue!

 When you look along the horizon you're actually looking through more atmosphere than when you look straight up. When the sun rises or sets, the light initially has to pass through more atmosphere than usual. Because of this, red light has a harder time getting through the atmosphere and is often scattered along with the blue light, making the sky appear reddish purple. You can thank astronomy for those pretty views!

Kepler's Planet Discoveries

The image below is today's Astronomy Picture of the Day. It's not a compilation of photographs,but a representation of stars that have planets orbiting them.

The Kepler mission was launched in 2009,with the goal of discovering Earth like extrasolar planets (i.e. planets that revolve around other stars besides our sun). To do this, Kepler looked at hundreds of thousands of stars and watched to see if they got any brighter or dimmer. If the brightness of a star dropped, it might be due to a planet crossing in front of it. We experience this all the time in our own solar system. When Venus appears to cross in front of the sun from Earth's perspective, the Sun looks dimmer by about 0.2%. It's not something we notice with our eyes, but telescopes can easily measure this subtle change in brightness. Using this method, Kepler found 1,235 potential exoplanets! The image above represents each host star (yellow/orange) and the planet crossing in front of it (black circles). Based on the data Kepler receives, we can figure out where the planet crosses the star (top, middle, bottom, etc.) and about how big it is. Telescopes today do not have the power to directly image most exoplanets, but Kepler's method proves incredibly successful. If you look closely at the image, you might even see some multi-planet systems!

Illustration Credit: Jason Rowe, Kepler Mission

Go to APOD.NASA.gov to see a higher resolution image

What's Your Sign? The True Zodiac

As much as I hate it when people assume that astronomy=astrology, I love sharing this little bit of information….

 

Your astrological or zodiac  sign (whether you’re a Libra, Taurus, etc.) has to do with the constellation that was highest in the night sky the day you were born. These constellations fall on the ecliptic, which is the path that the planets take across the night sky. There are 12 constellations and therefore 12 zodiac signs that appear for about a month at a time throughout the year. All this was put together by the ancient Greeks back a couple thousand years ago, and has been in pop culture ever since. There isn't a single newspaper nowadays that doesn't give you your daily horoscope. Well I'm sorry to disappoint all of you that live by your horoscope, but the zodiac sign you thought you were is wrong. (What! But my personality fit so nicely with my zodiac sign! How could this be true!) Pop culture never took into account that the stars and our solar system move. In the past couple thousand years, our solar system has revolved around our galaxy, and changed position enough such that the stars in the night sky don't appear at the same time that they used to thousands of years ago. So now instead of the Libra constellation being highest in the sky in early October, it's highest in early November. You can figure out your true zodiac sign using your birthday and the list below. Note that some people want to define a new zodiac called Ophiuchus, but it hasn't really been accepted into pop culture yet.

Capricorn - Jan 20 to Feb 16

Aquarius - Feb 16 to Mar 11

Pisces - Mar 11 to Apr 18

Aries - Apr 18 to May 13

Taurus - May 13 to Jun 21

Gemini - Jun 21 to Jul 20

Cancer - Jul 20 to Aug 10

Leo - Aug 10 to Sep 16

Virgo - Sep 16 to Oct 30

Libra - Oct 30 to Nov 23

Scorpius - Nov 23 to Nov 29

Ophiuchus - Nov 29 to Dec 17

Sagittarius - Dec 17 to Jan 20 

I told this to someone the other day and they were devastated. They lived their life by their horoscope and couldn't believe that it had changed. Hope this doesn't burst your bubble!

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