Seeing Stars with James Wooten: Mars and Jupiter Shine Bright

This star map shows the Houston sky at 10 pm CDT on July 1, 9 pm CDT on July 15, and dusk on July 31.  To use the map, put the direction you are facing at the bottom. The Summer Triangle is high in the east.  This consists of the brightest stars in Cygnus, Lyra, and Aquila.  Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to his left.  Leo, the Lion, sets in the west with Jupiter.  From the Big Dipper’s handle, ‘arc to Arcturus’ and ‘speed on to Spica’ in the southwest.  Mars and Saturn remain in the south at dusk.

This star map shows the Houston sky at 10 pm CDT on July 1, 9 pm CDT on July 15, and dusk on July 31. To use the map, put the direction you are facing at the bottom.
The Summer Triangle is high in the east. This consists of the brightest stars in Cygnus, Lyra, and Aquila. Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to his left. Leo, the Lion, sets in the west with Jupiter. From the Big Dipper’s handle, ‘arc to Arcturus’ and ‘speed on to Spica’ in the southwest. Mars and Saturn remain in the south at dusk.

Jupiter is now in the west at dusk. It outshines all stars we ever see at night, so you can’t miss it.

Mars and Saturn are now in the south at dusk. As you watch them, Mars is to the right and is much brighter.

Although Mars continues to fade each night as Earth leaves it farther and farther behind, this month Mars still outshines all of the stars and even rivals Jupiter in brightness! By the end of the month, Mars begins to approach Saturn.

Venus is lost in the Sun’s glare and out of sight all month.

The Big Dipper is above the North Star, with its handle pointing up. From that handle, you can ‘arc to Arcturus’ and then ‘speed on to Spica’; those stars are in the west at dusk. Leo, the Lion, is also in the west at dusk.

Antares, brightest star of Scorpius, the Scorpion, is in the south, with the ‘teapot’ of Sagittarius to its left. Saturn is right above Antares. The Summer Triangle has fully risen in the east. The stars of summer are here.

Moon Phases
Moon Phases in July 2016:

New July 4, 6:01 a.m.

1st Quarter July 11, 7:52 p.m.

Full July 19, 5:57 p.m.

Last Quarter July 26, 6:00 p.m.

At 11:00 am on Monday, July 4, Earth is at aphelion. This means that on this date Earth is as far from the Sun as it will get this year. But all of us can feel how hot and sticky it is outside now, compared to January, when Earth was at its closest. This is because the Earth’s orbit is almost a circle; the difference between closest and farthest distance from the Sun is small. Indeed, Earth is only 1.6% farther than average from the Sun on July 4. The effect of Earth’s 23.5 degree tilt easily dominates the tiny effect of Earth’s varying distance from the Sun.

Also on July 4, the Juno spacecraft enters Jupiter orbit. For just over a year and a half, Juno will execute 37 orbits of Jupiter before a controlled orbit into Jupiter in February 2018. The spacecraft is designed to explore the inner composition of Jupiter, giving more information about what’s far beneath the cloud layers we see.

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. As of now, however, George is closed while Brazos Bend State park dries out from yet another round of floods on the Brazos River. The park could reopen as early as July 12.

Clear Skies!

James G. Wooten
Planetarium Astronomer
Houston Museum of Natural Science

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.

654 - Galaxies - Seamless Texture
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.