Hertzsprung-Russell diagram

 

The Hertzsprung-Russell, or HR, diagram is the number one tool of astronomers. Basically, the HR diagram is graph that relates observable quantities of a star such as temperature, brightness and amount of light emitted . We can use this information to group stars into different categories, called spectral types, which we label by the letters OBAFGKM (As random as it seems, there is some logic behind the lettering. I'll explain in a later post). After years of observations, astronomers have discovered an age sequence that is often drawn over the HR diagram (the line in the graph above). After a star is born, it begins on the main sequence at a moderate brightness and temperature. Over time, the star evolves into a giant or supergiant star and changes its position on the HR diagram, heading towards the upper right hand corner where temperature and brightness are high. When the star dies, it plummets leftward and down on the HR diagram, getting colder and dimmer.

The beauty of the HR diagram is this: Astronomers can use telescopes to measure the brightness, amount of light emitted, and temperature of a star. They then place it on the HR diagram and viola we now know its rough age and spectral type! We can then compare it to stars of the same type and age and learn so much more about the star, just by looking at one graph. Such a wonderful tool!

Solar vs. Lunar Eclipse

A friend of mine asked me what the difference between a solar and lunar eclipse was, and I thought it would be an excellent topic for ADYK!

 A solar eclipse is what most people think of when they hear about an eclipse. This is when the full moon crosses directly between the sun and earth, blocking out some or all of the sun's light. A total solar eclipse is when the moon blocks out all of the sun's light, allowing us to view the solar corona. The sun's corona is the super hot plasma surrounding the sun that's only visible with special telescopes, and during solar eclipses. The next partial solar eclipse will occur on July 1st, but few will see it as it will only be visible from a small region in the middle of the Antarctic ocean.

 

A lunar eclipse occurs when the moon passes behind the Earth in just the right spot such that the Earth's shadow falls on the moon, blocking the sun's light from reaching it. Lunar eclipses can be seen from anywhere on Earth the night they occur, unlike solar eclipses that can only be seen from a tiny portion of the planet. This is because of the orientation of the moons orbit with respect to earth's rotation. The next total lunar eclipse visible from the US is April 15, 2014.

Syzygy!

Syzygy of the Sun, Moon and Earth

Ok admit it… you really want to know what syzygy means don't you? No I didn't make it up, it actually has something to do with astronomy! When the sun, Earth and the moon or another planet all happen to line up in a straight line we call that a syzygy (pronounced "siz-i-jee"). To be honest I had never heard this before until I stumbled upon a website of random astronomy facts, and this was one of them! Syzygys (syzygies?) occur during a lunar or  solar eclipse, and when Mercury or Venus crosses in front of the sun from Earth's point of view. Sometimes syzygy is used to describe a strange formation of the planets, such as when they are all on the same side of the sun.  According to Google it's also the name of a few restaurants, a Japanese band, and a type of god in the Gnosticism belief system. I think next time something astronomically cool happens I'm going to give it a fun name and see if it sticks….

Image credit: NASA

Star Formation

 

 

Ever wonder how stars form? Astronomers have been thinking about that for quite a while, and are pretty sure they have a good idea about how it works. Stars form out of giants clouds of gas and dust in space. The tiny particles bump into each other until they stick and form a large ball of gas. This protostar, as astronomers call it, gravitationally attracts the cloud of gas surrounding it and increases in size until most of the gas has fallen onto the star. What's left is a big ball of gas surrounded by a disk of dust particles which accretes (falls onto) the star. Some of the dust in this circumstellar disk will stick together to form rocks, and a few may even grow big enough to be planets! After about 10 Million years (yes million!) the star will accrete most of the dust and become a "young adult" star, or Zero Age Main Sequence star. The star is now big enough and hot enough to burn Hydrogen in its core (left side of diagram). If the star doesn't accrete enough gas and dust to become large enough to burn hydrogen, it becomes a brown dwarf (right side of diagram). Most of the stars that you see in the night sky are average main sequence  stars of various sizes and ages.

Ring Around The.... Planets?

Open a new tab in your internet browser (yes, right now). Go to Google and pull up an image of Saturn (I don't care that you know what it looks like, just do it). Remember that picture, and look up a picture of Jupiter, Uranus and Neptune as well. Now if I start singing the song "One of these things is not like the other…" what would your answer be?...... The answer I was going for was Saturn! What's so different about Saturn? Well as you saw from the picture, Saturn has a beautiful ring structure and the other planets don’t….. Wrong! Believe it or not, all of the gas giant planets have rings! (Now if you didn't actually go to Google before, I bet you are now just to see if you can find a wiki page on ringed planets to see if I'm right.) 

 

Saturn's ring structure is very bright and prominent because it is thick and made mostly of ice which reflects light. The rings around Jupiter, Uranus, and Neptune are much thinner and are mostly made of rocks. Pictures of each planets rings are shown above. There's a big black spot over Neptune because Neptune is so bright compared to its rings that the planet's light needed to be blocked out so the rings were visible . Now when someone refers to Saturn as the ringed planet you can say "actually, all the gas giants have rings… but I know which one you mean."

Image credits: NASA/Voyager/J. Rayner/NSFCAM/IRTF

Week of Moons: Titan

Silly me forgot to post the final week of moons update on Friday, as blogspot was down Friday morning. So here is the final Week of Moons post about Titan. It ties in nicely with today's post about Cassini-Huygens.

 

Titan, the largest moon of Saturn, is one of my favorites. Why? Well take a look at the infrared picture above (bottom left) and tell me what it looks like….. Earth! Titan is very much like Earth was way back when it was just a baby, about 4 billion years ago.  It's about half the size of Earth and has a dense nitrogen atmosphere. It's the only moon in our solar system that has a thick atmosphere, and the only object to have flowing liquid and lakes on it! Unfortunately these lakes are not water lakes, but methane lakes (too toxic for humans to swim in!) There are also volcanoes which spew out  water and methane (cryovolcanism), suggesting that there might be a layer of liquid water underneath Titan's crust! Astronomers think that Titan may be the best place to look for life in our solar system, as it is so similar to Earth. The Huygens Lander discovered in 2005 that the surface of Titan contains carbon compounds, further supporting the idea of possible life! Now we don't expect to find an alien civilization walking around, but we may find bacteria or other organisms who've adapted to the conditions and are living either on the surface or in the methane lakes. NASA and ESA are planning robotic missions to land on and study Titan, but no official announcements on when this will occur have been made. I guess we will just have to wait and see!

Image Credit: NASA/JPL/Cassini-Huygens

Cassini-Huygens Mission

The Cassini Huygens mission launched in 1997 with the purpose of studying Saturn and it's Earth like moon Titan. The spacecraft reached Saturn in 2004 where Cassini entered orbit around Saturn. Huygens landed on Titan about one year later. If you've ever looked at Saturn through a telescope it's absolutely spectacular. On a good night you can clearly see the rings and even some of the moons! It almost looks like someone put a scrapbooking sticker of Saturn at the end of the telescope, it's that clear. Cassini giving us an up close and personal look at the planets and it's moons;the image above being one of them. A 2 minute video of images Cassini sent back to Earth is the feature of today's Astronomy Picture of the Day. Check it out here

Image credit:

NASA/JPL/Space Science Institute