April is here! Get Ready to Celebrate Earth Day all month long in Houston.

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Well it’s that time of year again. Happy April everyone! With the April flowers come Earth Day celebrations. While the official Earth Day is April 22, Houstonians like to celebrate Earth Day every weekend in April. Even better, all these Earth Day events are free!

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Start out the month by bringing your recyclables to Discovery Green. April 4th is a recycling Saturday. Spend the day downtown or around Hermann Park (maybe even at HMNS?) and end your day at the Miller Outdoor Theater watching Legally Blonde the Musical (not Earth Day centered but still fun and free).

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April 11th is the big event at Discovery GreenEarth Day Houston sponsored by Air Alliance Houston. It’s the big event because that’s where HMNS and I’ll be. Not only will we have info and a cool game about how you can conserve energy, but also have BUGS. While it may not sound exciting to have bugs when you’re outside, these are bugs you can (and will want to) interact with. Come by and pet a tarantula. Don’t worry, when you stop by you won’t be bugging us.

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The Houston Arboretum has a slew of free events on April 18. Everything from a self-guided scavenger hunt to guided hikes and face painting. They will also have a plant sale.

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Exploration Green will host its first Earth Day on April 25. They will have a trail run, arts and crafts, kite flying and much more.

So take advantage of one or more of the Earth Day events. Brush up on your energy conservation at the Energy Conservation Club. See y’all out at Discovery Green.

Seeing Stars with James Wooten: Lunar Eclipse on April 4

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Mars remains in the west at dusk this month as it moves through Aries. Mars continues to fade a little each night as Earth continues to leave it farther behind. Later on this month, Mars begins to be lost in the glare of the Sun.

Mercury enters the evening sky as Mars leaves it. By April 30, Mars will be gone but Mercury will be low in the west northwest, near the Pleiades star cluster.

Venus is in the west at dusk. Look over the point of sunset for the brightest thing there.

Jupiter is now high in the sky, almost overhead, as soon as night falls. Jupiter outshines all stars we ever see at night, so it will be obvious when you look up at dusk.

Saturn is in the southwest at dawn.

Brilliant winter stars shift towards the west during April. Dazzling Orion is high in the southwest at dusk. His three-starred belt is halfway between reddish Betelgeuse and bluish Rigel. Orion’s belt points right to Aldebaran in Taurus the Bull. Above Orion are the twin stars Castor and Pollux, marking the heads of Gemini, the Twins. Jupiter is among the Twins this month. You can find Sirius, the brightest star we ever see at night, by drawing a line from Orion’s belt towards south (left as you face west). Forming a triangle with Betelgeuse and Sirius is Procyon, the Little Dog Star.

Joining the winter stars are stars of spring in the south and east. Look for Leo, the Lion almost overhead at dusk. In the east, extend the Big Dipper’s handle to ‘Arc to Arcturus’ and then ‘speed on to Spica’.

Moon Phases in April 2015:

Full April 5, 7:05 am

Last Quarter April 11, 10:44 pm

New April 18, 1:56 pm

1st Quarter April 25, 5:55 pm

The Full Moon of April 4 passes through the Earth’s shadow, causing a total lunar eclipse. Unfortunately, the Moon clips the edge of the Earth’s shadow, allowing for only 5 minutes of totality. What’s more, for us the eclipse occurs near moonset and sunrise (which are almost simultaneous when there is a lunar eclipse). That puts the Moon low to the horizon during the eclipse; only those with clear views all the way to the western horizon can get a good look. It also means that totality falls during morning twilight.

Eclipse times:

Partial eclipse begins: 5:15 am
Totality 6:57-7:02 am
Moonset (still partially eclipsed) 7:13 am

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement.

Ride on a Shooting Star: Space Fuel

After the decimation suffered during World War II, mankind took a look at all the new technologies he had created to fight the war and turned his gaze towards the stars. From the late 1940’s this onward and upward reach has helped to fuel the engines of our ingenuity, but what has fueled those stellar ambassadors that now dot our solar system and beyond.

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Creative Commons License photo credit: Patrick Hoesly

To move from the surface of the earth to this new ocean a rocket must be moving about 7 miles per second. That takes a lot of energy. Many different propellants have been used. The very first rocket fuels were a mix of kerosene and liquid oxygen. Alcohol, hydrogen peroxide, and liquid hydrogen have also been used, in addition to solid fuels. They can provide thrust without the need for all the refrigeration and containment equipment that some of the liquid fuels, such as liquid hydrogen and oxygen, require.

Once the probe is beyond the reach of the atmosphere there is no way to change what’s on board.

The probe cannot drop by the local Radio Shack and pick up a fresh pair of AA batteries. While the probe is being built on Earth, the engineers must make sure that they provide a source of power that will give the probe the right amount of power.

Too little power and the scientific instrumentation won’t work; too much power could over heat the probe. On board chemical batteries can be used, but they take space that could be used for scientific instruments. Solar panels can be used, but only up to a certain distance from the sun. Beyond the orbit of Jupiter, probes need an internal power supply that will last for years.

They use the heat from radioactive decay of fissionable isotope.

Sputnik 1 in Orbit Sep 10-4-57
Creative Commons License photo credit: FlyingSinger

Early probes like Sputnik and Explorer 1 used chemical batteries to power their systems. In March of 1958 Vanguard 1, the 4th artificial satellite and the 1st powered by solar power, was launched. Probes with solar panels have more space on board for scientific instruments than probes that use only chemical batteries. Probes sent into the inner solar system (sun to Mars) are almost all powered using solar arrays.

Mariner 2, the first USA probe to Venus, suffered the loss of one of its solar arrays, but because it was closer to the sun, it was able to operate using only one solar array. No American manned space craft have made use of solar arrays yet (the new Multi-Purpose Crew Vehicle may), the Russian Soyuz spacecraft have used them since 1967.

The International Space Station (ISS) is the largest man-made structure outside our atmosphere.

Larger than a football field (but smaller than a football pitch), this outpost orbits the earth every hour and a half. It is also powered completely by solar power. Past the atmosphere, solar power becomes more practical and more consistent (there is no night in space). Because of the orbital path of the ISS, it is eclipsed by the earth for 30 minutes out of every hour and a half. The station makes use of rechargeable batteries to make sure it is never without power.

From a Distance
Creative Commons License photo credit: Undertow851

As the probes go farther and farther away from the sun, the light that can reach them is less and less.

Until August of 2011, no probe to Jupiter had ever been powered just by solar panels. Juno, the latest probe to Jupiter, has the largest solar arrays given to a deep space probe and the first probe to Jupiter to use solar arrays.

Jupiter receives only 4% of the sunlight we enjoy on Earth. Advances in solar technology have now made it practical to use solar panels out 5 Astronomical Units (AUs) from the sun. All other deep space probes have used a radioisotope thermoelectric generator (RTG).

A RTG works by converting the heat from the decay of a radioactive fuel into electricity. American probes have been using Plutonium 238 (an isotope of Plutonium) since the late 1960’s. It has a half life of about 88 years. RTGs have powered all our interplanetary probes (the Voyagers and Pioneers and soon to be New Horizons). However, NASA has begun to run out of fuel for the RTGs and the creation of more is full of political and safety considerations.

There he goes, after an all day long work.
Creative Commons License photo credit: giumaiolini

The technology that we’ve made to go out to the ‘verse with will also help us here on the cool, green hills of earth. RGTs have been used, mainly by Russia, to provide power for off the grid light houses. Advances in solar panels for space are used down here on Terre Firma. With the reliably of solar power in space, there are even attempts to construct orbital solar collectors to beam down electricity. There will be from heaven to Earth more than is dreamt of.

Go Stargazing! September Edition

Venus and Mars have left Saturn behind in the night sky (check out my earlier blog on the position of the planets). You can spot the star Spica in between Mars and Venus during this time of year. (Spica is similar to Mars in brightness and closer to Venus than to Mars). 

 Cloud structure in The Venusian atmosphere,
revealed by ultraviolet observations

September is the last full month to observe Venus at dusk. That’s because Venus has by now come around to Earth’s side of the sun on its faster, inner orbit.  Thus, Venus now begins to overtake the Earth, passing between the Earth and sun on October 29.  We’ll therefore see Venus shift farther to the left of Mars and then drop down below it.  In October, Venus exits the evening sky quite quickly as it shifts back towards the sun.  September and October 2010 is an excellent period for observing Venus’ crescent phase in telescopes.  Anytime Venus is on our side of the sun, more of its night side faces us, resulting in a crescent like appearance when magnified.

Saturn is far to the lower right of Venus and Mars as you face west at dusk.  You’ll need a horizon clear of tall buildings and trees to see it before it sets.  You’ll also need to look early in the month, as Saturn is practically behind the sun by month’s end.  

Jupiter dominates this month’s skies.  On Tuesday morning, September 21, Earth aligns with the sun and Jupiter, bringing Jupiter to opposition (because the sun and Jupiter are then on opposite sides of the Earth).  On the night of September 20-21 we see Jupiter rise at sundown and set at sunup—Jupiter is up literally all night long.  During the whole month, though, Jupiter is visible virtually the whole night.  It outshines all stars in the sky, so it’s easy to find.  Face east in late evening or south southwest at dawn to see it.  The planet Uranus is less than one degree above Jupiter this month; the two planets are closest on September 18.

The Big Dipper is setting in the northwest at dusk; you now need a horizon clear of trees and tall buildings to get a good look at it. You can extend the curve of its handle to ‘arc to Arcturus’, which is in the west at dusk tonight.  Arcturus, by the way, is the fourth brightest star we ever see at night, but the brightest one Americans ever see on a September evening.

As the Dipper gets lower, look for five stars in the shape of an ‘M’ directly across the North Star from the Big Dipper’s handle.  This is Cassiopeia, the Queen—the ‘M’ is the outline of her throne.  Her stars are about as bright as the North Star and the stars of the Big Dipper, so she’s not too hard to find. 

星空下的汗腾格里峰 / Mt. Khan Tengri under Galaxy
Creative Commons License photo credit: livepine

High overhead, look for the enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair.   This triangle was up all night long from June to early August, hence its name.  Scorpius, the Scorpion, is in the southwest at dusk.  Sagittarius, the Archer, known for its ‘teapot’ asterism, is to its left.  Between these two star patterns is the center of our Milky Way—the brightest part of that band as wee see it.  On a cloudless night far from the big city, see if you notice the Milky Way glow near the ‘teapot’ of Sagittarius. 

Look for the Great Square of Pegasus rising in the east.  The vast stretch of sky under Pegasus is largely devoid of bright stars—ancients called this the ‘Celestial Sea”. 

Moon Phases in September 2010:

Last Quarter                  September 1, 12:22 am, September 30, 10:52 pm

New Moon                       September 8, 5:29 am

1st Quarter                     September 15, 12:49 am 

Full Moon                        September 23, 4:18 am

At 10:13 pm on Wednesday, September 22, the sun is directly overhead at the equator.  As a result, everyone on earth has the same amount of daylight and the same amount of night.  That’s why it is called the equinox (‘equal night’ in Latin).  In the Northern Hemisphere, we’ve seen the days get a little shorter and the midday Sun a little lower each day since June 21.  For us, the season changes from summer to fall at the equinox.  In the Southern Hemisphere, people have seen the days lengthen and the midday Sun get a little higher each day since June.  For them, the season changes from winter to spring.