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Welcome again to our monthly newsletter with features on exciting celestial events, product reviews, tips & tricks, and a monthly sky calendar. We hope you enjoy it!
If you go out every day at the same time, and measure the altitude and azimuth of the Sun, you will find after a year that the Sun has returned to the position it was in when you started your measurements. It will also have traced out a shape or a pattern, known as an analemma, in the sky.
Since you probably can't see the Sun every single day from where you live (e.g. because of weather), you can use Starry Night to make an analemma. You don't have to go outside, and it'll only take a few minutes rather than a year! Here's how:
Why the heck does the Sun do this? To find out, you might want to ask yourself some questions about the shape of the analemma, and you can use the dates marked on Starry Night's analemma to help you figure it out.
Tune in next month to check out the answers.
Brenda M. Shaw is not a very good skater and might ask the Sun for some coaching on that figure-eight thing.
Last time, we learned that the Sun reached its maximum northern declination around June 21 ushering in summer in the northern hemisphere. The northern latitude where the Sun is directly overhead at noon defines a great circle at about 23.5 º N known as the Tropic of Cancer.
But why “Cancer” when the Sun is actually in the constellation Taurus?
Summer Solstice 2010 AD
Because of the Earth’s axial tilt, gravitational forces exerted by the Sun and Moon cause its axis to wobble like a spinning top. As a result, the North Celestial Pole and the Celestial Equator move in relation to the stars in a process called precession.
This in turn, causes points like the equinoxes and the solstices to move westward along the ecliptic at the rate of about one constellation per two thousand years. This is only approximate since not all constellations are of equal width along the ecliptic and one precession cycle takes about 26,000 years.
So the Sun was indeed in the constellation Cancer when relevant observations about the summer solstice were made about two thousand years ago.
Another effect of precession is that Polaris, our current north star will not retain its title as time progresses. In 2010, Polaris is less than one degree from the North Celestial Pole but the separation was over 6 degrees about a thousand years ago.
To see how the North Celestial Pole wanders among the stars use Starry Night to run the file Precession.snf.
This month there are two questions regarding precession. We now know that the Sun is currently not in the constellation Capricorn at the winter solstice and Polaris is not always our North Star.
Check the next Starry Night Times for the answer.
Answer to last month’s question: At the summer solstice, the Sun has an altitude of 90º at the Tropic of Cancer (latitude 23.5º) and drops by 1º in altitude for every degree of latitude as we head north. Latitude 66.5º represents the lowest northern latitude at which the Sun does not set on summer solstice day. It is also known as the Arctic Circle.
Judging by the number of questions I see on Yahoo! Answers about this, it must be a popular exercise for teachers to assign their students. Properly implemented, it can teach students a great deal about the motions of the Moon and also the challenges of astronomical observation and research.
The idea is to observe and record the appearance and position of the Moon over a complete lunar cycle. This sounds simple, but students can find it a challenging exercise.
I have a suspicion that quite a few teachers assign the exercise without ever having tried it themselves, and are unaware of the difficulties which even a student with the best intentions may run into. So I urge teachers to try the exercise with your students.
Right at the outset, it seems that quite a few students will forget they have to do this project and, a month later, they will be on the internet frantically looking for pictures of the Moon for every night. So it’s important to remind them at some point every day, preferably at the end of the school day.
Usually things go smoothly for the first two weeks of the lunar cycle, from New Moon to Full Moon. Inevitably there will be problems with weather, and its important to warn kids ahead of time that as scientists they need to record negative observations as well as positive ones. So they should record every time they looked at the sky, including the date, time, and weather conditions. Once a night is not often enough, as they will often look when the Moon is simply not in the sky. It’s important to look in the late afternoon, early evening, just before bedtime, and first thing in the morning.
Many students have the mistaken belief that the Moon is visible only at night, so it’s vitally important that they also check the daytime sky. This becomes crucial in the two weeks after Full Moon, because the Moon rises almost an hour later every night, which soon puts it well past most students' bedtimes.
Often the best time to spot the Moon in the second half of the lunar month is around 8 a.m.
I would also urge the students, once they’ve located the Moon, to check on its position every hour or so, if that is practical. This will show them how the Moon moves across the sky, day or night. It’s especially important that they observe moonset (just after New Moon) and moonrise (around Full Moon); it’s amazing how many adults have never learned that the Moon, like the Sun, rises and sets every day/night.
A very large number of students “lose” the Moon right after Full Moon. They need to be reminded that the Moon is visible for close to 12 hours every single day, but those 12 hours are not always the same. Many of those hours are in daylight. This is a good place to use Starry Night to figure out exactly when the Moon rises and sets on a given day, using the Info pane.
When I see a student on Yahoo! Answers in panic mode over this assignment, I often suggest that they approach their teacher and request a second month to complete the project. Since learning about the Moon’s movements is more important than grading, I urge you to be open to such requests. This really is quite a difficult assignment because it requires children to be up checking the skies at times way outside their normal bedtimes. Some preparation of their parents for these tasks is also advisable.
Give your kids an advantage! When you refer their teacher to our educational solutions, the school will receive 10% off their purchase and you'll receive 15% off your next selection at the Starry Night Store!
Here's how it works:
Let us know if you've any questions, and thanks again
Solar System Boundaries
Press the Decrease Elevation button to fly through various solar system boundary layers. To identify the various boundary layers by color, click on the contextual menu button of the Sun in the Find pane and select Distance Spheres.
NGC 6960 & NGC 6992, the West and East Veil Nebulas, are part of the Cygnus loop, the remains of a supernova that exploded over 100,000 years ago. Two other sections, NGC 6995 and 6979 are close by.
M29 is an unimpressive open cluster, notable only in that it was one of the original discoveries of Charles Messier.
NGC 6819 is a small open cluster with about two dozen stars from 10th to 12th magnitude within a 5' circle. Its discovery in 1784 is attributed to Caroline Herschel.
Deneb, which marks the tail of the swan, is one of the 20 brightest stars in the night sky. Just three degrees away lies NGC 7000, the North American Nebula, so-called because of its obvious shape. This is an active star forming region and quite large, though it's difficult to see without the aid of astrophotography.
M39 is an open cluster, and is a nice binocular object with 30 or so stars spread over its seven lightyear diameter. It's also "pretty close" to Earth, at "just" 800 lightyears.
Finally, NCG 6826, the Blinking Nebula, gets its name from an odd phenomenon: its central star appears to blink on and off when you look toward and away from it quickly.