Star Struck

New Horizons Update

As the New Horizons spacecraft closes in on its July flyby of Pluto, its cameras capture ever higher resolution images.  Here is a link to the latest released images.  It’s starting to get real!


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Posted in Solar System, Spacecraft

A Cosmic Dance

The two brightest planets in the sky right now—and the two brightest planets, period—are Venus and Jupiter. Shortly after sunset at the end of April, Venus is the very bright object in the west, and Jupiter is only a little less bright high in the southern sky. In actual fact, they never get very close to each other. Venus orbits closer to the sun than does Earth, and Jupiter much farther from it. At their closest, Venus and Jupiter are well over 400 million miles apart: four and a half times the distance between the Earth and the sun.

But if astronomy teaches us anything, it is that what you see very much depends on where you stand. From our vantage point on Earth, Venus and Jupiter sometimes appear to be quite close to each other. And at the end of June, they will be less than half a degree apart, less than the width of a full moon. Such an apparent meeting of two celestial bodies is called a conjunction.  Here is a view of the sky at 9 pm tonight (April 24, 2015) as seen from Lynchburg, Virginia.

Venus Jupiter April 1

When we look at the sky, it’s easy to see how our ancestors imagined it as a bowl, with all the celestial objects about the same distance away from us. In fact, it has enormous depth, with some objects like the moon quite close, and others like Jupiter much farther away. Its three-dimensional nature is not readily apparent.

If we take a different perspective—if we stand in a different place—we can see how two objects that appear to be close together do so only because they lie along the same line of sight. Here is a view from above the solar system. In this view, the Earth’s north pole is directly below us, and all the planets orbit the sun in a counter-clockwise direction.

Venus Jupiter April 2
At the end of April 2015, Venus and Jupiter lie in different directions as viewed from the Earth. But as the planets orbit the sun, those nearer the sun move faster. Venus closes on the Earth as the weeks pass, and at the end of June it is much nearer to us. The more distant Jupiter meanwhile has moved only a little along its nearly twelve year long path.

Venus Jupiter Conjunction 2
On the evening of June 30/July 1, the two will be at their closest approach, less than the width of your finger held at arm’s length.

Venus Jupiter Conjunction 1
The weeks leading to that night will be rewarding as well, as we watch the two brightest natural sky objects after the sun and the moon approach each other in a cosmic dance, and as we remind ourselves that a different location in the solar system would provide a very different view.


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Posted in Planets, Sky Phenomena, Solar System

Ceres Awaits

Dawn is sneaking up on Ceres from behind.

On March 6, this well-traveled spacecraft slipped into orbit around the dwarf planet (or asteroid; take your pick) after having spent 14 months orbiting the asteroid Vesta and more than two years in transit to Ceres. But Dawn’s approach to Ceres is from its unlit side. Pictures taken on the approach to orbit revealed two bright spots that have scientists intrigued as to their nature. The best guess is water ice, but the details await higher-resolution images.

In this diagram below of the approach to Ceres, the view is from the side, with Ceres’ north pole at the top of its disc, and the sun to its left. I’ve darkened the unlit side of Ceres to make this more obvious. Dawn’s current (April 18) approximate position is marked by the yellow X. The white circles mark one day intervals along the path.

You can see that for the last several weeks, Dawn has had only Ceres’ dark side in view. Once the spacecraft is in its initial science orbit, it will be able to see the entire surface as it rotates beneath. But we finally have some images released of the sunlit north pole of Ceres. Enjoy this animation as we await the unveiling of yet another previously unexplored solar system body!



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Getting to Pluto

What were you doing on January 19, 2006? If you were in any way connected to the New Horizons mission to Pluto, you were at the Kennedy Space Center in Florida to watch it being launched on its long journey. I chose this video for the audible reactions of the onlookers as much as anything. A rocket launch is a thrilling event!

When New Horizons began its journey, Pluto had not yet been demoted to “dwarf planet” status. Still, for most people, it marks the outer boundary of our solar system, the farthest outpost on the way to the stars. Getting there requires a very fast ship.

Getting anywhere in space is always a trade-off between how fast you can get there and how big a payload you can transport. A limiting factor for both is how big a velocity boost you give your mission at the outset. Once most interplanetary missions have achieved orbit around the Earth, they use very powerful chemical rocket engines that burn for a matter of minutes but change the spacecraft’s velocity significantly. (There are exceptions; see this article about the Dawn spacecraft.) They then coast for months or years on the way to their destination. The resulting trajectory is a long and curving one, as planets and spacecraft all orbit the sun. For example, this is the path taken by the Curiosity rover spacecraft to Mars:

So how do you get to Pluto?

Read more ›

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Bright Objects

In case you were wondering, the two very bright objects visible in the sky shortly after sunset are Venus (in the west) and Jupiter (in the southeast). After the sun and the moon, these are the two brightest natural celestial objects. If you see a star-like object even brighter than Venus that is slowly moving across the sky (and not blinking—those objects are called airplanes), it is probably the International Space Station (ISS). In its current and final configuration with widespread solar cells it outshines Venus, its brightness surpassed only by the sun and the moon. Here is the sky view at 8 pm on Thursday, March 26th from Lynchburg, looking to the south.  You’ll notice the bonus planet of Mars below Venus; look for its characteristic orange-red color.


Speaking of the ISS, there will be an especially nice viewing opportunity (for the Lynchburg area) this Sunday night, March 29th. The station will appear in the northwest at about 6:28 pm, pass almost directly overhead, and fade from view in the southeast at 6:34 pm. The sun will still be out but the station should be bright enough to see, especially if you know when and where to look.
As for the weather: I can’t help you there!

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Posted in Planets, Sky Phenomena

Earth Calling Dawn

On March 6, the Dawn spacecraft was captured by the gravity of Ceres which is, depending on your preferences, either the largest asteroid of the solar system, or one of many dwarf planets. On its approach, Dawn’s cameras took these images of the two hemispheres from a distance of 28,000 miles.

These are by far our best views ever of this object, but no new ones have been released since then. What’s going on? Is NASA hiding evidence of alien life?  Although I have to rank this speculation alongside the moon-hoax conspiracy theories in its utter lack of plausibility, I wondered myself about the lack of new data. So I did a little digging, and the explanation is both more prosaic and more interesting.

Here is a diagram of the path taken by the spacecraft on its approach, looking down on Ceres from above its north pole. The sun is out of the image to the left.

The white circles are at one-day intervals, and the closer together they are, the more slowly the spacecraft is traveling. Today, on March 18, Dawn is near the apex of this path, moving only at 37 miles per hour relative to Ceres, getting ready to fall back toward its target picking up speed as it does so. You can see from this that it is now farther from the dwarf planet than it was on its approach.

Dawn has a remarkable rocket engine on board, an ion propulsion system that can operate for months at a time.

Its thrust is almost nothing (equivalent to the force of a sheet of paper on your hand), but operating over long periods of time allows it to move the spacecraft around the solar system, albeit quite slowly. If the spacecraft’s engine were shut down just as it entered orbit, it would loop around Ceres in a long elliptical path. Instead, it continues thrusting to put Dawn into a close circular orbit with an altitude of 8400 miles. And that orbit is a polar one, which allows it to image the entire surface. This shows the same orbital approach, this time from the side. North is up and the sun is again out of the image to the left.

So…no NASA conspiracy. No aliens. In a week or two we should be getting some spectacular closeups!

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Time on the Clock

If you are as I am, among those who think the people responsible for Daylight Saving Time, while not necessarily evil, are at least deluded…then let’s talk about clocks and time.
One of the arguments I hear when I engage in my semi-annual rant against DST is this: “It’s all just arbitrary anyway. What does it matter?” Granted, hours and clocks are human inventions, but they are inextricably tied to astronomical cycles. A day is the time that our planet takes to turn once on its axis. A year is the time Earth takes to travel once around the sun. Noon is the middle of the day, at least when we are on standard time. Sort of. Let’s take a closer look.
For those of us in the northern mid-latitudes (Lynchburg is at 37.4° N), the sun is nearly always in the southern part of the sky. It travels from east to west during the day, from our left to our right as we face the south. When it reaches its highest altitude, it is directly south. This is local noon.

local noon

But here’s the thing. Shift your position just a few miles east or west and that time will be different. At Lynchburg’s latitude, go a little over 50 miles east or west, and there will be a four minute difference in the time of local noon.
In times before long-distance travel and communication, this didn’t really present a problem. Each settlement kept its own time by a sundial, and no one really concerned themselves with such fine divisions of time as whether it was 9:32:28–roughly half past nine o’clock was close enough. It was the advent of railroads, first in Britain and then in the U.S., that brought about the need for some standard of time. Even so, it was not until 1918 that the current system of time zones was set by law in the U.S. Clock time is the same throughout a time zone, and each time zone is centered on a longitude where solar time is the same as that zone’s clock time.
The Eastern Time Zone in which Lynchburg lies is centered at 75 degrees west longitude, five time zones west of the prime meridian, the 0° longitude line that runs north and south through Greenwich, England.


Lynchburg’s longitude is a little more than 79° west, so our local noon is a few minutes later than 12:00 (or 1:00 when DST is in effect). We’re not that far from the center of the Eastern Time Zone, so the difference is not large. At the boundary between one time zone and another, the difference can jump from clock time being significantly earlier than solar time to being significantly later.
Political considerations obviously play a part in where time zone boundaries are set. In the U.S., Indiana probably holds the record for the most confusing divisions.  In China before 1949 and the Communist takeover, China had a very sensible five time zones. From 1949 forward, the entire country observes a single standard time, although in the far western provinces there are unofficial variations. For China’s easternmost province, this leads to the ridiculous clock time for sunrise on July 1 of 3 am! This map beautifully illustrates worldwide offsets between solar time and clock time.

Our clock time is geared as closely as is practical to solar time without having multiple different clock times for nearby locations. Except, of course, when we observe Daylight Saving Time. I’ll close with a story that is almost certainly not true, but ought to be. Supposedly a Native American chief who first heard of DST remarked “Only the white man’s government would be so stupid as to cut a foot off the top of a blanket, sew it onto the bottom, and think they have a longer blanket.”


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Posted in Sky Phenomena

Dwarf Planets and New Planets, Oh My!

Just about the time that one NASA spacecraft is closing in on Ceres (formerly known as an asteroid, now semi-officially designated as a dwarf planet) and another nears its encounter with Pluto, a group of astronomers has suggested that there may be two or more planets at the outer reaches of our solar system. Didn’t we settle this when we kicked Pluto out of the family of planets?

To keep it short: planet is a word with no universally agreed-upon scientific definition. A very good summary of the subject is here for those who want to dig deeper. But let’s talk about Ceres and the possible “extra” planets.

Ceres and Dawn

dawn approaching Ceres

The Dawn spacecraft is amazing for a number of reasons:
• It uses an ion propulsion engine to navigate its way around the inner solar system.
• It was the first spacecraft to orbit Vesta, the second-largest asteroid and the fourth discovered.

• It will be (in March 2015) the first spacecraft to orbit Ceres, and therefore the first spacecraft to orbit two different asteroids. Here is the latest (January 13th) series of images from Dawn as it approaches Ceres. These will rapidly improve as Ceres draws nearer!

I hesitate to predict what we will find once we are there. Such predictions nearly always turn out to be wrong! Stay tuned.

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First Steps to Deep Space

Tomorrow (December 4th) morning at 7:05 am EST, the first uncrewed test flight of NASA’s new human spacecraft will lift off from the Kennedy Space Center in Florida.

For those of us who remember the Apollo moon flights of the ‘60s and ‘70s, the Orion capsule is very familiar.

It is indeed a return to basics for America’s crewed space missions. The space shuttle was a remarkable machine, but it brought to mind the classic comment about a camel being a horse that was designed by a committee. Space flight is of course inherently dangerous. The position of the shuttle orbiter, strapped to the side of an enormous fuel tank and solid rocket boosters rather than at the top of the rocket with an escape system—well, we’ve all seen how this contributed to the loss of two shuttles and their crews.
So what is different about the Orion capsule? For starters, it is bigger. The Apollo command module squeezed three astronauts into a volume of 218 cubic feet (imagine a cube of 6 x 6 x 6 feet). Orion will accommodate four crew members in a roomier cabin of 316 cubic feet. Its attached service module is also designed for longer-duration missions, and for excursions into deep space—beyond the moon’s orbit. On such missions to an asteroid or to Mars, crew members would spend their time in an attached habitat, using the Orion to get to space and back to Earth.
Like the Apollo spacecraft however, Orion has to withstand the stresses of atmospheric re-entry at speeds far above those of a vehicle re-entering from low Earth orbit. A Soyuz returning from the International Space Station hits the atmosphere at roughly 17,000 miles per hour. Coming back from a lunar or a deep space mission means velocities up to 25,000 miles per hour at the top of Earth’s atmosphere. A craft designed to return from such missions has to be sturdy.
And of course the flight controls and computers on board are fifty years more advanced than on Apollo. The computer that landed men on the moon was far less capable than the phone you carry in your pocket.
This test flight is designed mostly to test how well Orion withstands that fiery re-entry. A Delta IV Heavy booster will take the capsule to an altitude of 3600 miles; re-entry speed should be around 20,000 mph. This high-altitude flight will also take it through the inner Van Allen radiation belt, testing the radiation shielding for the craft’s electronics (and ultimately for its human crew.)

NASA is a government agency, subject to the shifting political winds blowing out of Washington. So I will refrain from making any predictions about future missions and limit myself to this: it’s about time, and I will be watching! You can do the same here.

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October 8 2014 Lunar Eclipse

Just a quick post to show you this great eclipse photo from my friend Mike Overacker, shot with a Canon 6D and a 600 mm lens at f/5.6.  The small dot to the left and slightly above the Moon is the planet Uranus.  Thanks for sharing, Mike!


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