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!

Next Topic: Why is the sky blue?

Cat's Eye Nebula

Some of the most beautiful and iconic images in astronomy are those of planetary nebula. This is a picture of the Cat's Eye nebula. Planetary nebula, despite their name, have absolutely nothing to do with planets. They are the result of a violent explosion of a star similar in size to our sun. Star's like our sun will live about 10 billion years. After this time, the star will puff up and become a red giant. As the star progresses through its final stages of life, it collapses on itself and if the pressure becomes too high it explodes, leaving behind a planetary nebula. Astronomers are actively studying these objects in hopes to learn a lot more about them. 

Next Topic: What's Your Sign?

Halley's Comet

Halley's comet is probably the best known comet by non-astronomers. It flies by earth once every 75-76 years and is visible without a telescope. It last appeared in 1986, so many readers may have seen it. I, unfortunately was not born yet, so I have to wait until 2061 to see it. Records exists dating back to roughly 240 BC referencing sight of the comet.

The comet is peculiar in that it revolves around the sun in the opposite direction of the planets. Looking down from the "north" all the planets orbit counterclockwise, while Halley's comet orbits clockwise. It has a bright head full of rocky material with shocked gas in front of it. The tail is due to the solar wind stripping material from the comet, illuminating it,  and pushing it away from the head.

There's been some talk in the non-scientific literature that Halley's comet will someday crash into and destroy Earth…. Well to comfort your nerves it's probably not going to happen. It's really difficult to calculate the path of Halley's comet because it is heavily affected by the gravity of the sun and other planets. Computer models show that in 2134, Halley will reach it's closest point to earth: 8,077,826 miles away. This is still 36 times farther away than the moon. So unless the sun or Jupiter influences Halley's orbit enough to send it hurdling towards Earth, we should be fine.

Thanks to Nick Ruffle for this post idea!

Next Topic: Cat's Eye Nebula

Super Moon Tomorrow Night!

Get your cameras, telescopes, eyes and coffee ready…. You're going to be doing some moon gazing this weekend! This month's full moon occurs tomorrow night, and this one is extra special. The moon is going to appear 14% larger and 30% brighter than it has in almost 20 years!

Why is this happening? Well, as you probably know, the moon orbits around the Earth in an almost circular shape called an ellipse (fancy word for oval). The moon makes one complete orbit around earth every 27 days, and since the orbit is an ellipse, it reaches a closest point to earth once every 27 days. The moon goes through a phase cycle as well, and we see a full moon once every 29 days.Every 18 years or so, the timing is just right so that the moon is full and it's at its closest point to Earth. Tomorrow is that day! So don't miss the spectacular super-moon tomorrow, because you won't get a chance to see this for another 18 years!

Thanks to Angelica Rodriguez for this post idea!

Next topic: Next Topic: Halley's Comet

Image credit: Michael Richmond, Valerie Rapson, Marcus Freeman; WIYN 0.9m telescope at Kitt Peak, Az

The Habitable Zone

As the search for extraterrestrials continues, astronomers have tried to narrow down the best places to look for Earth like planets and human life. To do this they've defined a region in space called the habitable zone.

The habitable zone is defined as the distance from a star at which an Earth like planet can harvest liquid water (and potentially life).  It's often referred to as the Goldilocks Region, because it's "not too hot and not too cold".  Lucky for us, Earth is at just the right distance from the sun to form life. The other planets in our solar system are too hot or too cold to have liquid water, so it's not such a big surprise that we haven't found life elsewhere in our solar system. 

You can define a habitable zone around size of star. Stars bigger and hotter than the sun have a habitable zone farther away from it, while small cooler stars have a closer habitable zone (blue shading on the graph). Astronomers have actually found a few planets that are in the habitable zone around other stars in our galaxy! The problem with most of them is that they are big and gaseous, like Jupiter, and therefore don't have a solid surface for life to live on. There is high hope, though, that  the Kepler Space Telescope (launched last year I believe) will discover Earth like planets in the habitable zone in the next few years!

Next Topic: Halley's Comet