Star Struck

Total Lunar Eclipse

In the early pre-dawn morning hours of Tuesday, April 15th, most of the Western Hemisphere will witness a total lunar eclipse.  Totality (when the Earth completely blocks the Sun as seen from the Moon) begins at 3:07 am EDT and ends at 4:25 am EDT.  Those in other time zones can adjust as needed.  The official NASA eclipse information is here.

Solar and lunar eclipses occur when the Sun, the Earth, and the Moon line up so that one body is blocking another as seen from the third body.  A lunar eclipse such as Tuesday night’s requires this sort of alignment.

The terms penumbra and umbra can be confusing, but here is what they mean.  Within the umbra, the Sun’s disk is completely obscured from view by the Earth.  Within the penumbra, only part of the Sun’s disk is obscured.  A total lunar eclipse occurs when the Moon passes into the umbral shadow of the Earth.

Since the Earth is much larger than the Sun as seen from the Moon, the Moon can spend a fairly long time passing through Earth’s umbral shadow.  Tuesday morning’s total eclipse lasts well over an hour, and that’s not even counting the time when the partial eclipse begins (1:58 am EDT) and ends (5:33 am EDT).  The exact size of the shadow depends on the distance between the Earth and the Moon at the time of eclipse, but the difference between the maximum and minimum shadow sizes is not that large.

Total solar eclipses are an entirely different story.  The necessary alignment is this.

As seen from the Earth, the Sun and the Moon are very nearly the same apparent size.  Another way of saying this is that the umbral shadow of the Moon is quite small when seen from the Earth.  Total solar eclipses do not last long (the longest possible is around seven minutes), and totality occurs only along a narrow strip of Earth’s surface.  One generally has to travel to see a few fleeting moments of the Sun’s being blocked out during the day.  But speaking as one who has done so, the sight is well worth the effort.

The good news is that lunar eclipses are much more accessible.  And if you don’t want to stay up that late or get up that early next week, you can mark your calendar for the night of September 28th, 2015.  A total lunar eclipse will begin that night at 10:11 pm EDT, and end at 12:27 am EDT the next morning.

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Posted in Sky Phenomena, The Moon

The Latest News From The Big Bang

It won’t make you richer. It won’t organize your calendar. It probably has no practical application whatsoever. But the scientific discovery announced on March 17th is one of the great discoveries of the new century, and virtually certain to result in a Nobel Prize. (Appropriate note of caution: assuming this is confirmed and stands up to peer review.) Here is a link to an article by Dennis Overbye, the long-time science writer for the New York Times.

In the question-and-answer format that follows, I’ll try to explain what the new discovery reveals and what was actually discovered. I hope it will neither annoy those who really, really know this stuff nor blow away those whose last science course was in high school! Get comfortable and settle back, because this will take a while. Maybe set aside two sessions.

What exactly was discovered?

Patterns in the polarization of radiation from the cosmic microwave background (CMB). Yeah, I know—geek talk. Let’s try and break that down to standard English.

In the early 1960s, two competing cosmological theories stood on roughly equal ground. Steady State theory acknowledged the expansion of the universe that had been detected decades earlier, but it still maintained that the overall universe did not change with time. “Continuous creation” filled in the gaps left by universal expansion; the universe billions of years ago and billions of years from now would not look any different over galactic scales of distance.

Steady State

The competing Big Bang theory discarded the idea of continuous creation, and asserted that the expansion meant that the average separation between galaxies would be greater five billion years from now than it is now. More to the point, the theory “ran the clock backward” to a hot early universe that was much smaller than today’s.  The average separation of galaxies would increase over time.

Big Bang

A successful scientific theory is one that makes testable predictions. A hot early universe would have cooled as it expanded, not by radiating heat away like a coffee cup, because there is nothing to radiate it away to–there is no “away”. You just have the same amount of energy distributed throughout a much larger universe. A universe with an average temperature of 3000 K expands by a factor of 1000, and its average temperature becomes 3 K.

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Posted in Cosmology

March/April 2014 Sky Watcher’s Guide

This will be an every-two-months guide to what you can see in the night sky, geared to mid-latitude northern hemisphere observers. The original post with more detailed guidance can be found here. What can you expect to see in March and April 2014?

March

Daylight Saving Time: March is one of the two months of the year in which we have to account for this abomination. Since the 15th of the month comes after the Congressionally determined switch back to standard time, the times are all Eastern Standard. Don’t get me started.

Moon Phases: New on March 1st and March 30th ; full on March 16th

Planets: Jupiter continues to dominate the early evening sky in the far western reaches of Gemini. Although he is traveling a little farther east each night relative to the background stars around him, Earth’s orbital path around the sun puts those background stars a little farther west each night, at a faster pace than Jupiter’s motion. The net result is that Jupiter will be quite low in the west in a few months–but not for a while!

Neither Mars nor Saturn show on the chart, but you should know that Mars rises around 11 pm in mid-month, and Saturn about two hours after that.

We need to give a nod to Venus, impossible to miss in the morning sky before sunrise. Because Venus is an inferior planet (it orbits closer to the Sun than does Earth), it goes through phases similar to the Moon’s. But because, unlike the Moon, Venus varies considerably in its distance from us, its apparent size in each phase is noticeably different. This should help you see why.

phases_of_venus

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You Can’t See That From Here

Take a look at this beautiful time lapse video of the night sky.

Ah, if only we could find nice dark skies, we could see such sights ourselves, right?  Well, no.  Actually, you would need to travel to Australia (where this video was shot) or some other place equally far south of the equator.  The sky we see from the Northern Hemisphere is not the same sky that our Southern Hemisphere friends see.

Imagine an astronaut, properly space suited of course, floating free in space between the planets, so far from Earth that it is just a bright point in an infinitely black sky.  She can see stars in every direction because there is nothing to impede her 360 degree view.

Standing on the surface of the Earth has its advantages—no space suit is needed for starters.  But that 8,000-mile thick ball of rock does block the view a bit.  It’s so big that it looks pretty flat to us, so it’s sort of like standing on a big table, one that is definitely not transparent.  We’re not going to see anything that is under the table, that is in the direction of our feet.

The way that table is oriented to the sky depends on where we are on the Earth’s surface.

Put that “table” at a different spot, and we see a different part of the sky.

Why does it only matter how far north or south we are, and not how far east or west?  The Earth rotates from east to west, and will bring sections of the sky that are out of our view to the east into sight as it spins on its north-south axis.  Only at the equator itself can you see all of the sky, both the northern and the southern halves.  The north celestial pole, very near the North Star Polaris, would be on your northern horizon and the south celestial pole on your southern horizon.  If you move farther south, Polaris slips below your horizon and will stay there unless you move back in a northerly direction.

Most of the Earth’s land mass and consequently its population lie north of the equator.  But many (I only barely refrained from saying most) of the sky’s most spectacular sights are in the southern celestial hemisphere, visible only by traveling south.

Let’s take a guided tour of that video at the top of the page again.  Our Milky Way Galaxy surrounds us in a belt of stars that we can see from any point on Earth.  But its central region, rich with star clusters and nebulae, is lost in murk near the horizon from most of the northern hemisphere.  From the southern part of the Earth, it is often high overhead.  That is what you are seeing in the first few seconds of the video—our glorious galaxy showing its most star-packed neighborhoods.  Starting at about 0:45, two fuzzy patches appear that start out to the right of the Milky Way’s band.  These are the Large and Small Magellanic Clouds (LMC and SMC), so named because Magellan was the first European to see them on his globe-girdling voyage.  They are companion galaxies to our own Milky Way, much smaller than our home galaxy, about 160,000 light years away for the LMC and 200,000 light years away for the SMC.

See those dark bands that seem to denote an absence of stars in some parts of the Milky Way?  That is not an absence of stars—it is the presence of obscuring gas and dust which is concentrated in the plane of the Milky Way.  It is the raw material out of which stars and planets form, and of which you and I are made.

In the sequence that starts around 2:15, you should see a familiar constellation at the left.  Don’t recognize Orion (three stars in a line for its “belt”; four stars in a rough rectangle surrounding them) when it is upside down?  Australians might dispute who in fact has the right perspective on Orion.

Travel is a wonderful experience in and of itself.  When you have new things to see above you as well as around you, it is even better!

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Printable Star Charts

For those of you found the star charts in the previous post to be useful, you may want something you can print out without draining all the black ink or toner you have. These are the same star maps, but in a different format that has more white space than black. Each of them is set at 10 pm Eastern Standard Time on the 15th of the month, and the views are those seen from Lynchburg.

The first two are for January, first looking south and then looking north.2014 January South Chart

2014 January North ChartAnd these two are for February, first looking south and then looking north.2014 February South Chart

2014 February North ChartEnjoy!

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2014 Sky Watcher’s Guide

You know all those New Year resolutions that you have already broken? I fully intended to post this at least a week ago. Ah well, better late than never…

This post is intended to introduce people to the habit of skywatching, and once the habit is ingrained, to be sure that you will never walk outside, day or night, without at least a glance over your head. Not a bad habit to gain.  Each month throughout the year (there go those resolutions again!) I intend to post a similar update for your information, and repost the background information as well. Since I am so late in the month of January, I am posting information here for February, too.  I haven’t assumed any optical aid beyond a good pair of binoculars. There is plenty to see even without them.

WHAT IS INCLUDED IN EACH MONTH’S INFORMATION

Moon Phases: Full moon nights are good mostly for reading—outside by the light of the moon, or inside with a good reading lamp. They aren’t much good for sky gazing since the brightness of the moon pretty much overwhelms everything else in the sky. Nights with a new moon are dark, and that allows you to see dimmer objects that might otherwise escape your notice. Between the new and full phases, the moon waxes as more and more of its visible surface is illuminated, and it rises ever later. When it is full, it rises at sunset and sets at sunrise, visible all night long. Between the full and the new phases, it wanes, and if you confine your sky gazing to the early evening before midnight, it may not rise until well after you are done.

But the moon itself is a fascinating object, the closest and most easily observed extraterrestrial object. It especially comes into sharper view with binoculars. Look at the moon when it is less than half illuminated, and look along the line separating the illuminated surface from the dark. There the Sun is low in the lunar sky and casts long shadows that throw the deep craters and the tall mountains into higher relief. See if you can spot a bright central peak poking into the sunshine from the dark floor of a deep crater. The best online lunar map I have found is here.

Planets: I’ve confined myself to the five planets that are visible to the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. For views of Earth, look down.

Meteor Showers: I haven’t tried to include every single one of these, only the ones that might be worth your while to stay up for. The moon phase greatly affects how many meteors you will see; the ideal situation is when a shower occurs during a new moon. The radiant is the point from which the meteors appear to originate; the showers are named for the constellation in which the radiant appears. This is an optical illusion in the same way that railroad tracks appear to meet in the distance; the meteors actually follow parallel paths as illustrated below:


Deep Sky: There are only a few objects beyond the solar system that are visible to the naked eye (other than stars, of course). Even there you need a pretty dark sky. Binoculars will help, and I’ve included some of the more easily spotted objects.

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Posted in Sky Phenomena

Stars of the First Magnitude

No, we aren’t talking about Tom Hanks or Meryl Streep. These are the stars you see in the sky at night. If you have ever been confused by statements like the following, then let’s see if we can help you out.

  • “On 29 November 2013, the coma dimmed to an apparent magnitude of 5. By the end of 30 November 2013, the coma had further faded to below naked-eye visibility at magnitude 7.” (from the Wikipedia article about Comet ISON)
  • “As it is configured now, the ISS has an apparent brightness, or “magnitude,” of around -3 (lower numbers denote brighter objects on this scale), said Joe Rao, SPACE.com’s nightsky columnist.”

As with so many conventions of math and science, it all goes back to the Greeks. Among the many achievements of Hipparchos, one of the greatest astronomers of antiquity, was the creation of the stellar magnitude scale. He assigned a value of 1 to the twenty brightest stars (stars of the first magnitude), all the way down to stars that were barely visible to the naked eye, to which he gave a value of magnitude 6. A modified version of this system is still in use.

Telescopes have extended our vision to encompass objects too dim for naked eye observation. For example, the star known as Kepler 62, with five known planets in orbit around it, has a magnitude of 13.75. What about objects brighter than the brightest star, such as Venus? The only other direction to go from 1 is to zero, and from there to negative numbers. The magnitude of Venus (it varies as its phase and distance from us changes) can be as bright as -4.6. The sun’s magnitude is -26.7.


That’s the quick and dirty. Now for the details—and the complications.

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Posted in Sky Phenomena, Stars

Shopping for a Telescope?

When you are an “astronomy guy”, around this time of year you get inquiries from friends looking to buy a telescope as a Christmas present. Often this is for a child or a grandchild, but sometimes the friend is shopping for him or herself. I must admit to skepticism when someone is willing to spend $1000 on a telescope for their four year old—just exactly who is this telescope for? :-)  But my role is not to judge, just to provide information and to make recommendations.

I want to make it clear that these recommendations are based on my personal experience from childhood until now. My first telescope (at age 10) was an inexpensive reflector from the Sears Roebuck catalog, and my current instrument is a top-of-the-line refractor. I see a lot more with my current scope than I did more than fifty years ago—I know a lot more, too—but I’m not sure I derive any more pleasure from its use. A different astronomy person would probably give you a different list. What that reflects is the wonderful range of options available today. When I built my own telescope in the late 1970s, it was better than anything I could have bought ready-made at the same price. In my opinion you are better served today buying that ready-made scope unless you are skilled in a number of areas beyond being able to use a tape measure, an electric drill and a screwdriver. That’s about all that was required for me in 1979!

Vendors

DO NOT, REPEAT, DO NOT buy anything from a store that does not specialize in telescopes. What you get there is cheap plastic junk. There are wonderful showrooms scattered around the country, but most people probably do not want to drive that far. The good news is that two vendors (Astronomics and Orion Telescopes) I have used extensively both have wide selections online and excellent customer service. These are certainly not the only vendors available! If you want to get an idea of what is out there, just pick up the latest issue of Sky & Telescope at your local newsstand. These are simply the ones with which I am most familiar.

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Posted in Observatory and Telescopes

Will It Be a Spectacle Or a Speck?

Spectacle or speck?

OK, I stole that phrase. But it’s just too good not to use.

Comet ISON will very soon be upon us. The image above was taken with the Hubble Space Telescope when ISON was a little over four times as far away from the sun as is the earth. Starting in mid-November, it will get ever lower in the eastern sky just before dawn. If it survives its passage very near the sun, we could see it again in early December. But will it be the “comet of the century” promised earlier this year? Or will it join the infamous Comet Kohoutek and numerous other over-hyped comets as a disappointment for the general public? At this point no one really knows, although prospects for the former are—ahem—fading.

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What “Gravity” Gets Wrong

Let’s establish a few things at the very beginning. I love movies about space. I quite happily go along with improbabilities like warp drives, phasers, Vulcan mind melds and the concept that every extraterrestrial species we encounter will be remarkably humanoid. My very favorite science fiction trope is time travel, as unlikely a physical concept as there is. So I most certainly enjoyed the recent movie Gravity, starring Sandra Bullock and George Clooney, and I would recommend it to anyone as a gripping story and spectacular visual feast. Still, there was this quietly persistent voice in the back of my head sputtering “But, but…you can’t do that!” Will these sorts of things keep you from enjoying the movie? Well, they didn’t keep me from enjoying it, and I am probably the biggest science nerd that most of you know. Without giving away anything that isn’t in the trailer, I’m going to focus on the most egregious of these scientific boo-boos.

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Posted in human spaceflight, Spacecraft