There is one question we all have to ask when a beautiful comet graces the skies…
Comet C/2007 N3 Lulin on the evening of 26 Feb 2009Where to look?
Like any other solar system object, comets move against the sky. Even worse, when close to the Earth or Sun they can be moving so quickly against the stars that coordinates quickly become out of date. Aiming a telescope using coordinates a day old, or sometimes even only an hour old will result in a view of empty sky. A few stars perhaps, but no comet.
You need a table of coordinated calculated for regular time intervals, an ephemeris. Alternately you need a set of coordinates calculated for the exact time you will be looking.
Living south of the Tropic of Cancer we get to experience an interesting phenomena that folks outside the tropics will not see. There are two days each year when the Sun passes directly overhead. In the islands this event is called Lahaina Noon.
Spring Lahaina Noon for 2013
Location
Date
Time
Hilo
May 18th
12:17pm
Waimea
May 19th
12:20pm
Kahului
May 24th
12:23pm
Honolulu
May 26th
12:30pm
Lihue
May 30th
12:36pm
Lahaina noon occurs twice each year as the Sun appears to move northwards with the spring and again as it moves southwards in the fall. For the islands of the Hawaiian archipelago the first day is between May 16th and May 31st. The second Lahaina Noon will be between July 10th and July 25th.
The date on which this event occurs each year depends on your exact latitude, the further north the later in the spring it will occur. Thus the day for Lahaina noon will vary by eight days from Hilo to Honolulu, and another five to Lihue. As you approach the Tropic of Cancer at 23°26’N Lahaina Noon will occur closer to the summer solstice. The date will also slip a little due to the out of sync nature of our seasons and our calendar. This is the reason we insert a leap year into the calendar every four years.
This year Lahaina Noon will occur on May 18th for residents living in Hilo, or May 26th for Honolulu. It is also important to remember that the Sun is not directly overhead at 12:00 exactly. As the islands lie west of the center of the time zone, true local noon occurs up to half an hour after 12:00.
Presenting the wonders of the night sky to the general public can be a rewarding experience. The smile on a child’s eyes they first time the see the rings of Saturn or the craters of The Moon is a truly a wonderful thing.
A Halloween princess watching moonrise through the telescopePublic observing can also be a daunting challenge to the inexperienced public presenter. A little preparation and thought can prevent a lot of trouble and make it a better experience for both the presenter and the public.
I am attempting to put down a few of the things I have learned in over a decade of hauling a telescope around. In that time I have used countless schoolyards as observatories, set my gear up at posh resorts, on the tee line of a driving range, outside the front door of Wal-Mart, across the fence from cows at a dude ranch, parking lots, city sidewalks and grassy lawns, under conditions both perfect and absolutely lousy for doing astronomy. Dealt with everything from drunks to two year olds, and I still do this regularly… It is worth every young smile!
To quote Douglas Adams… “Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is.”
We are accustomed to using miles or kilometers when considering distance. These are the distances that we experience in our everyday lives. Driving to work or the supermarket, we do not travel very far compared to the distances faced by those who study the stars. Those wanting to discuss distances beyond our little planet, the distances to the stars and galaxies face a quandary… The universe is just too big, when using these familiar units the number of zeros become impractical and the numbers cease to be convenient, or even understandable. To express distances in the cosmos, astronomers just need a bigger tape measure.
The Andromeda Galaxy, 2.5 million light years awayWhen expressing distances among the stars we turn to the same phenomena we use to observe the stars, starlight itself. We know that light travels fast, covering huge distances very quickly. Light, just another form of electromagnetic energy, is a universal constant across the universe, how far it travels in a given time is a convenient standard by which to measure the universe.
In a few minutes light travels across our solar system, in a few years it can reach the nearby stars. Thus a distance unit that makes sense in astronomy… The light-year, the distance light travels in a single year. With this we have a convenient unit of distance, one that links the concepts of distance and time. A simple bit of math converts the light-year into familiar units… 9.45 trillion kilometers or 5.86 trillion miles.
As our Sun continues through the current solar maximum we should have plenty of opportunities to view one of the most sublime of all natural spectacles, the Aurora Borealis.
A strong auroral display over St. Johns Harbor, Alaska on the evening of September 4, 2012While traveling in Alaska and other northern regions there is always a possibility of a good showing. To make the most of the opportunity a little information cane be useful…
Solar Activity
Solar activity waxes and wanes in an eleven year cycle. When active there are increased numbers of sunspots and solar flares. It is this activity that can have such a dramatic effect here on Earth. A strong solar flare can be accompanied by a release of enormous quantities of material from the Sun. Called a coronal mass ejection (CME) this material streams outwards from the Sun. If the Earth happens to be in the path this material will strike the Earth’s magnetic field, causing the field to distort and reverberate with the impact. Charged particles are channeled into the atmosphere along the magnetic field to create a glowing spectacle.
Our current solar maximum should run through 2013 and into 2014 providing excellent auroral viewing conditions for the next year or two.
When doing any sort of public astronomy, showing folks the beautiful sights available to a telescope, I often hear the question “Can I take a photo of that?” The person asking the question is usually holding the ubiquitous compact digital camera. They are often surprised when my answer is “Yes”.
Taking a photograph of the Moon using afocal photography
It is indeed possible to manage hand held shots of bright astronomical objects by simply holding the camera up to the eyepiece. There are a few tricks to making it work, but nothing that can not be demonstrated in a minute or two. The resulting photographs can be quite pleasing, definitely worth showing to friends and family along with the rest of the Hawai’i vacation shots.
The method of positioning a camera with a lens in front of an eyepiece is called afocal photography, or sometimes digiscoping. Afocal has been around for a while, but was not considered a practical photographic method by most. The advent of common digital cameras without removable lenses has changed this.
I have completed the first set of the Astronomy Basics posts I intended to do. I really wanted to get these posted as support material for the astro-events posts.
As I finished these I realize I should probably continue and hit a few more subjects. Look forward to a few more Astronomy Basics posts in the coming months.
Throughout the descriptions of astro-happenings here on Darker View, I use the terms degrees, arc-minutes, and arc-seconds. This is how astronomers measure size and separation of objects in the sky.
The degrees used by astronomers are the same as those you learned in high school geometry, the same as marked on that old school protractor forgotten in the back of the desk drawer. 360 degrees mark a circle, 360 degrees reach once around the sky.
Degrees measure rotation, and just about everything in astronomy rotates… As the Earth rotates on is axis, the sky goes wheeling overhead. When we move a telescope from one point in the sky to another we rotate the telescope about its axis. How far does it rotate? That is measured in degrees.
Watching meteors is one of the simplest forms of astronomical observing. Just about anyone can enjoy meteor watching, from just about anywhere in the world. Enjoying the show takes only a couple things… A dark sky and a comfortable place from which to watch.
A pair of Leonid meteors streak through OrionMeteors are simply small bits of debris hitting the Earth’s atmosphere at very high speed, typically tens of thousands miles per hour. Our solar system is rich with this debris. Most of these bits are quite small, about the size of mote of dust or a grain of sand. Something the size of a pea would create a spectacular fireball that lights up the whole sky. While they often seem close, they are actually quite high, 60 miles (100km) above the ground when they flare into short lived fireworks.
The mechanism for the show is simple. When something hits the very thin air high in our atmosphere at very high speed it compresses the air in front of it. This compression also heats the air, causing it to glow white hot. Heated enough, the air becomes a plasma, the molecules shredded and electrons freed from the atoms. It is not the meteor itself that you see, but the glowing plasma around it.
There are a number of questions many people ask about meteor observing. You can find many of the answers below. Watching a meteor shower takes no special equipment, expert knowledge or extravagant preparation. This is an activity nearly anyone can enjoy, one of the spectacles of nature available to all.
Does the Moon seem a little larger and brighter than usual? It may not be an illusion, sometimes the Moon really does look a little larger or smaller in the sky.
Like all orbiting objects, the Moon does not orbit in a perfect circle, but rather in an ellipse. This means that as it orbits it is a little further away or a little closer. In the case of the Moon the difference is not much, but you can see it, if you know to look.
The apparent size of the moon as seen at perigee versus apogeeWhen the Moon is furthest from the Earth, a point called apogee, it will be about 405,000km (251,000miles) from the Earth. While at perigee, the Moon will be about 360,000km (223,000miles) from the Earth, as measured from the center of the Earth to the center of the Moon. The change in distance leads to a noticeable difference in the size of the Moon as seen by an observer here on Earth. When at perigee the moon will appear about 12% larger than when seen at apogee.
Click to view a simulation of a lunar month showing phase, libration (tilt), and the size change as the Moon goes from apogee to perigee. Image credit Tomruen via Wikimedia CommonsThe difference is most noticeable at full Moon. If the full Moon occurs near apogee or perigee, an experienced skywatcher can spot the difference. The effect should not be confused with the well known Moon illusion, where the Moon can appear larger near the horizon.
The period of time between full Moons, the synodic month, is about 29.5 days. While lunar perigee occurs every 27.5 days, an anomalistic month. Since these periods are not equal, the cycle drifts in and out of phase. About once a year the cycles coincide and full Moon and apogee or perigee will occur near the same time.
At apogee, the Moon will be appear about 29 arc-minutes in size, a little less than half a degree. At perigee the Moon will be about 33 arc-minutes across, a bit more than half a degree. The numbers may not seem like much, but it is a visible difference. The simulated images shown here will give a better idea of what the numbers represent.
This change in size and distance leads to the moonlight being a bit brighter at perigee than at apogee, about a 30% difference. So if that moonlit night seems brighter than you remember it may actually be the case.
