Astronomy Wrap-Up -- Transits, Planets, and Constellations

This week, we started by reviewing the moon phases and what eclipses are.

A lunar eclipse happens when the sun, earth and moon are lined up in a way that causes the earth to block the sun's light from reaching the moon.  So, for a small amount of time, what would have been a full moon instead looks like a new moon, but then the earth's shadow moves and it's a full moon again.  A type of lunar eclipse happened just a few days ago, you can read about it here.

A solar eclipse happens when the moon happens to perfectly line up such that it blocks the suns' light from reaching the earth.  The only reason the moon, which is so tiny, can do this is because it is so close to the earth, just like when you put your thumb close in front of your eye, you can block your view of an entire person.  But if your arm is outstretched, your thumb can only block your view of a small thing.  This picture is a pretty good illustration of what happens.  Here is a site from NASA that details eclipses that have happened and are going to happen.  On November 3, we are going to experience a rare hybrid solar eclipse -- awesome!!

Next, we talked about transits.  A transit is when an object, such as a planet or a moon. crosses in the path of the sun, but the object is too small and/or too close to the sun to actually block out much of the light.  You see (if you looked at the sun, which we humans should never actually do!) a small, black circle move across the sun.  We are the third planet, so the inner two planets do transits once in a while, and here's a picture of a Venus transit from 2004.  Another one happened in 2012, and the next will not be until 2117.  So we who are alive today will never get to see one!  :(  There are Mercury transits too, but since it is so much smaller and closer to the sun, it is an even tinier black circle.

Then, we discussed the three planets in our solar system we hadn't gotten to before:  Saturn, Uranus, and Neptune.

Saturn is the planet most well known for its rings, but actually, Jupiter, Uranus and Neptune all have rings too.  It has seven rings with gaps and divisions, and the rings are thought to be pieces of comets, asteroids, or shattered moons.  A day on Saturn lasts only 10.7 hours, but a year lasts 29 Earth years.  Saturn's atmosphere is hydrogen and helium, and its core is rock, ice, water, and other compounds, with a layer of liquid metallic hydrogen around it.  Saturn has superfast winds and rising heat that make the yellow and gold bands we see on the planet.  Saturn's largest moon, Titan, is larger than Mercury and has a nitrogen atmosphere similar to what Earth's may have been long ago.

Uranus is the planet with the equator at nearly right angles to its orbit, and it rotates in the opposite direction of the other planets.  This may be explained by a past collision with an Earth-sized object.  It looks blue due to methane in its atmosphere, and one year on Neptune lasts 84 Earth years.  Seasons on Neptune last 20 years, and inside the planet is icy water, methane, and ammonia.  Uranus has 27 known moons, and they are mostly named after Shakespearean characters, unlike the moons of the other planets, which are named for Greek mythology characters.  There is a swarm of 8 small satellites that are very crowded, and it is a mystery why they haven't crashed into each other.  Neptune is nearly a twin of Uranus in size and composition.

Neptune is a slightly different shade of blue than Uranus, because of other components than methane in the atmosphere.  A day takes 16 hours, and a year takes 165 Earth years.  There are 13 moons and 6 rings, and only one mission has visited Neptune -- Voyager 2.  Its magnetic field is 27 times stronger than earth's, and it has very strong winds.  Neptune was the first planet found by mathematical calculations before it was actually observed.  Triton is its largest moon, and it is extremely cold.  Icy geysers were seen on this moon, and it is getting closer to the planet every year.  In millions of years, it might break apart and create a bright ring around Neptune.  The atmosphere is getting warmer, and we don't know why.

Constellations are groups of stars that people observe on earth and create a picture out of them.  They are actually moving very slowly across the sky, because we are on the surface of a planet that is rotating.  We can't see the same constellations as people at a different latitude because of what direction into outer space we are facing.  The constellations that cross the same line as where the planets in our solar system are make up the zodiac.  There are twelve zodiac constellations, and a total of 88  constellations that people have defined (created).  The twelve zodiac signs are the horoscope signs, Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces.  The constellation for your sign is high in the sky at noon during the month of your birth, and people have observed them for centuries.