Light pollution is a major problem, both for professional and backyard astronomers. It used to be that if you just went out into the countryside, you could get decent viewing. But with unshielded mercury vapor lamp street lighting all over cities, you can't do that, anymore. City glow extends for tens, even hundreds, of miles, fogging up the sky.
The Vancouver Museum in British Columbia, Canada is currently hosting an exhibit of simple, practical solutions to a variety of modern problems. One of the items on display is something called "Lunar-Resonant Street Lights": http://www.indexaward.dk/index.php?option=com_content&view=article&id=95&Itemid=77
These are street lights that are sensitive to moonlight. They are brightest during a New Moon and dimmest (even off) during a Full Moon. Their inventors say that not only could these lights save "between 80 and 90 percent of energy normally spent on street lighting" but that they could also get people back in tune with the natural rhythms of the world around them, like lunar phases and star rotations. Check it out. It's a very interesting idea. Now, if we can just get rid of those infernal mercury lights...
Showing posts with label Paula R. Stiles. Show all posts
Showing posts with label Paula R. Stiles. Show all posts
Thursday, August 13, 2009
Thursday, July 9, 2009
Lunar and Solar Eclipses
We had a lunar eclipse on July 7 and there's a solar eclipse on July 21. The lunar eclipse was only visible from the western U.S. and points further west into the Pacific, but the next one on August 5-6 will be visible on the east coast, as well (in the evening just after sunset). The solar eclipse will be visible in China but not in the western hemisphere.
A lunar eclipse occurs when the earth is directly between the sun and the moon, thus blocking any direct solar radiation. This leaves the moon illuminated only by "earthlight", which makes it glow an eery red. This is because the bouncing back and forth through atmosphere causes the shorter, bluer wavelengths to be absorbed, leaving the longer red wavelengths.
A solar eclipse occurs when the moon is directly between the sun and the earth. Since the moon's orbit is not right on the ecliptic plane (the plane on which the earth revolves around the sun), this doesn't happen every month. You can guess the time of an eclipse (lunar or solar), however, by looking at a calendar that has both the date and the time of the full and new moons. A lunar eclipse only occurs during a full moon and a solar eclipse only occurs during a new moon because those are the only times when the moon crossing the ecliptic plane coincides with the earth or moon blocking the sun.
There are many solar and lunar eclipse calculators online. NASA has a good one:
Solar Eclipse: http://eclipse.gsfc.nasa.gov/JSEX/JSEX-index.html
And this one comes from the Naval Oceanography Portal:
Lunar Eclipse: http://www.usno.navy.mil/USNO/astronomical-applications/data-services/lunar-ecl-us
As a rule, partial eclipses are more common than total eclipses and lunar eclipses are more common than solar eclipses. I've seen several total lunar eclipses, but only two partial solar eclipses (I would have seen a third one when I was a kid, but heavy cloud cover hid it).
In addition to total and partial lunar eclipses, there are also "penumbral" eclipses, in which the moon darkens a little from the earth's shadow but not much as in a partial/total eclipse. Both this month and next month's eclipses are penumbral.
A lunar eclipse occurs when the earth is directly between the sun and the moon, thus blocking any direct solar radiation. This leaves the moon illuminated only by "earthlight", which makes it glow an eery red. This is because the bouncing back and forth through atmosphere causes the shorter, bluer wavelengths to be absorbed, leaving the longer red wavelengths.
A solar eclipse occurs when the moon is directly between the sun and the earth. Since the moon's orbit is not right on the ecliptic plane (the plane on which the earth revolves around the sun), this doesn't happen every month. You can guess the time of an eclipse (lunar or solar), however, by looking at a calendar that has both the date and the time of the full and new moons. A lunar eclipse only occurs during a full moon and a solar eclipse only occurs during a new moon because those are the only times when the moon crossing the ecliptic plane coincides with the earth or moon blocking the sun.
There are many solar and lunar eclipse calculators online. NASA has a good one:
Solar Eclipse: http://eclipse.gsfc.nasa.gov/JSEX/JSEX-index.html
And this one comes from the Naval Oceanography Portal:
Lunar Eclipse: http://www.usno.navy.mil/USNO/astronomical-applications/data-services/lunar-ecl-us
As a rule, partial eclipses are more common than total eclipses and lunar eclipses are more common than solar eclipses. I've seen several total lunar eclipses, but only two partial solar eclipses (I would have seen a third one when I was a kid, but heavy cloud cover hid it).
In addition to total and partial lunar eclipses, there are also "penumbral" eclipses, in which the moon darkens a little from the earth's shadow but not much as in a partial/total eclipse. Both this month and next month's eclipses are penumbral.
Thursday, June 25, 2009
Chasing the New Moon
For about six months now, I've been trying to catch the first day that you can see the crescent moon in the first quarter of its cycle. I never seem able to get closer than the second day. Have caught the second day before the New Moon, maybe even the last day, but not right afterward.
Monday was the New Moon and I tried to catch it yesterday. But despite a half-clear sky, what clouds there were seemed to congregate over the setting sun (I suspect there's an actual metereological reason for this involving the concentration of solar heat in the west at that time of day, but haven't worked out what just yet). So, I didn't see it until tonight, when it was a bit more than a sliver.
Due to the usage of the lunar cycles in many religious calendars, astronomical observation is actually a critical matter of good religious observance. Yes, for all of the denigration of religion in some quarters as antiscience, religious calendars are in fact heavily based on science, especially astronomy.
For example, there was considerable dispute over when to start Ramadan among Muslims until easy and quick reporting from Mecca became available. It doesn't seem like much to non-Muslims, but for Muslims, Ramadan is a holy month. If you start and end it too early, you're doing the wrong thing. If you don't start it once the moon reappears in the sky, you're doing the wrong thing. Think of it as if Christmas were based on the lunar calendar: you would want to know the exact date, but the date would be partially dependent on good astronomical observation--and weather.
Passover and Easter are also regulated by a lunar calendar--or, they were originally. Because they are so strongly connected to the spring (i.e. a solar/seasonal calendar), the lunar part of their calculation is restricted to a period in spring of about two months. This is why both float around the spring months of the calendar each year. And because the Christian aspect of Easter was originally a Passover festival, the two festivals not-infrequently fall on the same date.
Monday was the New Moon and I tried to catch it yesterday. But despite a half-clear sky, what clouds there were seemed to congregate over the setting sun (I suspect there's an actual metereological reason for this involving the concentration of solar heat in the west at that time of day, but haven't worked out what just yet). So, I didn't see it until tonight, when it was a bit more than a sliver.
Due to the usage of the lunar cycles in many religious calendars, astronomical observation is actually a critical matter of good religious observance. Yes, for all of the denigration of religion in some quarters as antiscience, religious calendars are in fact heavily based on science, especially astronomy.
For example, there was considerable dispute over when to start Ramadan among Muslims until easy and quick reporting from Mecca became available. It doesn't seem like much to non-Muslims, but for Muslims, Ramadan is a holy month. If you start and end it too early, you're doing the wrong thing. If you don't start it once the moon reappears in the sky, you're doing the wrong thing. Think of it as if Christmas were based on the lunar calendar: you would want to know the exact date, but the date would be partially dependent on good astronomical observation--and weather.
Passover and Easter are also regulated by a lunar calendar--or, they were originally. Because they are so strongly connected to the spring (i.e. a solar/seasonal calendar), the lunar part of their calculation is restricted to a period in spring of about two months. This is why both float around the spring months of the calendar each year. And because the Christian aspect of Easter was originally a Passover festival, the two festivals not-infrequently fall on the same date.
Thursday, June 11, 2009
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