Plus more also, too!

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/

http://www.youtube.com/watch?v=0fKBhvDjuy0

http://www.atlasoftheuniverse.com/

http://sunshine.chpc.utah.edu/labs/cosmic_zoom/cosmic_zoom2.swf

http://physics.weber.edu/schroeder/software/zoomer.html

http://htwins.net/scale2/
WAY COOL

Again, worth seeing:

http://www.essex1.com/people/speer/model.html

http://rense.com/general72/size.htm

FUN.

Play.  Comment.  Enjoy.

http://www.stumbleupon.com/su/2jRGYC/dd.dynamicdiagrams.com/wp-content/uploads/2011/01/orrery_2006.swf/

Note the difference between Copernican and Tychonian worldview.  In Tycho's view, planets orbited around the Sun, which in turn went around the Earth.  He was "splitting the difference" between a Ptolemaic view and a Copernican one.

http://www.solarsystemscope.com/

http://www.essex1.com/people/speer/model.html

http://rense.com/general72/size.htm


The epicycle issue:

http://astro.unl.edu/naap/ssm/animations/ptolemaic.swf

More about this to come.  This is just a sneak preview.

Constellation project

Friends!

For your constellation project, due in 2 classes, arrive at the following:

Some relevant image(s)
Some relevant mythology, if applicable
Some relevant astronomy

Enjoy!  Feel free to make your "presentation" formal or informal, as you wish.  We're talking about 5 minutes here, but I would like a copy of your notes (or powerpoint, if you use one).  And handout is helpful, but not necessary.

UT, from wikipedia

http://en.wikipedia.org/wiki/Universal_Time

Constellations

Constellations

http://www.astro.wisc.edu/~dolan/constellations/constellation_list.html

http://www.astro.wisc.edu/~dolan/constellations/constellationmonth_list.html

http://en.wikipedia.org/wiki/List_of_constellations



Also useful:

http://www.astro.wisc.edu/~dolan/constellations/

A discussion on Time

A discussion on Time

The second is the fundamental unit of time. It was originally defined as:

- the amount of time required for a 1-m pendulum to swing from one side of arc to the other

Now, it is defined as:

9 192 631 770 cycles of radiation corresponding to the transition between two hyperfine levels in the ground state of Cesium-133

Worth noting:

There are approx 365 1/4 mean solar days in one solar year (watch time). The mean solar day is the average length of a solar day, 24 hours.

Solar year - the time between 2 vernal equinoxes. This is actually the tropical year, which is growing shorter by 0.5 sec/century. 19000 is the standard tropical year.

Sidereal time - time by the stars

Sidereal year - the amount of time for the Sun to return to a given position among stars

Calendars:

Julian - 365 days with an extra day every 4 years (leap year)

This was still a bit imprecise - consider that in 1988, the year was 365 d, 5 h, 48 min, 43.5 s.

By 1582, the Julian calendar was out of phase with Easter by nearly 10 days. So, Pope Gregory XIII adopted a new calendar; 10 days were dropped from that year.

Gregorian calendar -

Years evenly divible by 4 are leap years. Every 4th century year is a leap year (2000, 2400; NOT 1600, 1700, 1800, 1900, 2100)

Daylight savings time

Changed a few years back. Now:

Starts at 2 AM, second Sunday in March - set clocks AHEAD 1 hour

Ends at 2 AM, second Sunday in November - set clocks back

We are EST, Eastern Standard Time. During DST, we become EDT (Eastern daylight time).

GMT

Greenwich Mean Time; 5 hours ahead of EST. Roughly the same as Universal Time (UT).

UT

Universal time

Basically the mean solar time as measured on the Greenwich meridian, thus, 5 hours ahead of us.

Formally, UT is defined by a mathematical formula as a function of sidereal time and is thus determined by observations of stars.

Sidereal time

In 365 1/4 solar days, Earth makes 366 1/4 rotations on its own axis. So, there are 366 1/4 sidereal days in a solar year. Each sidereal day is shorter by about 4 minutes than a solar day. UT and GST agree at one instant every year (at the autumnal equinox, around Sep 22). Thereafter, the difference between them grows, in the sense that ST runs faster than UT until exactly half a year later, when it is 12 hours. Another half-year later, the times again agree.

Local Sidereal Time

the hour angle of the first point of Aries

Greenwich Sidereal Time

local sidereal time on the Greenwich meridian

Julian Date (JD)

Jan 1, 4713 BC is the fundamental epoch from which this is decided. The Julian date is the number of days since this day.

There is no year 0 in astronomy. The year before 1 AD is defined as year 0. So, 10 BC is the year -9 in astronomy.

That trick again: to go from BC year to astro year, subtract one and change sign.

Notes on space

Notes on space

Coordinate systems:

On Earth:

Longitude

half-circle lines from North to South pole
Zero longitude runs through the site of the Royal Greenwich Observatory in England - the Prime Meridian (0 degrees long.)
Number of degrees east or west of the PM

Latitude

Full circle lines parallel to the equator (0 degrees latitude)
+ or - 90 degrees corresponds to the poles

International Date Line (IDL)
Near or along 180 degrees longitude line, through the Pacific Ocean
As we travel eastward around the globe, the hours get later roughly each 15 degrees (a time zone). When we cross the IDL, we go BACK one day. This keeps only 24 hours on the Earth at a time.


In the Sky:

Celestial Equator

imaginary line above the Earth's equator

Right Ascension (RA)

Celestial analog of longitude (both measure east-west)

Measured in hours (each hour of RA equals 15 degrees) along the celestial equator

Declination (dec)

Celestial analog of latitude (both measure north-south)

Measured perpendicularly above (+) or below (-) the celestial equator

RA and dec form a coordinate system fixed to the stars. To observers on Earth, the stars appear to revolve every 23 h 56 min. So, the coordinate system appears to revolve at the same rate. Of course, it is the Earth which is really moving (most noticeably).

Ecliptic

Although the stars are fixed in their positions in the sky, the Sun's position varies through the whole range of RA throughout the year. This path (the "apparent" path of the Sun) is called the ecliptic and is inclined 23.5 degrees with respect to the celestial equator (CE), since the Earth's axis is tipped by that amount. (The "ecliptic plane" is the plane that the Earth and Sun make.)

The ecliptic and CE cross at two points:

Vernal equinox

March 21 (approx)

the first day of Northern Hemisphere spring

the zero-point of RA

Sun's declination is 0 degrees

Nearly equal amounts of day and night

Autumnal equinox

Sep 23 (approx)

the first day of autumn

Sun's declination at 0 degrees

Nearly equal amounts of day and night

Two other noteworthy days:

Winter solstice

Dec 22 (approx)

Shortest day of the year in Northern hemisphere

9.5 h of daylight (in the DC area)

As you travel farther north, the days are even shorter

- in Anchorage, Alaska, the day will be 5 h long

- in Barrow, Alaska, the sun will not "come out" at all; noontime is like deep twilight

the North pole is angled most steeply away from the Sun

Summer solstice

June 21 (approx)

longest day of the year in the Northern hemisphere

amount of tipping toward Sun is greatest for N. hemisphere

Sun highest in sky (dec is 23.5 degrees)

Length of daylight depends on latitude, calendar date, but not longitude

Each point on the globe receives an average of 12 hours of light each day. So, students in Barrow, Alaska have several days of endless sunshine as well.

Since the Moon goes around the Earth, its RA changes through the entire range of values each month. Since its orbit is inclined to the CE, its dec also changes.

The Celestial Sphere

Celestial sphere sites

http://www.cascaeducation.ca/CSA/CSA_Astro9/files/multimedia/unit1/celestial_sphere/celestial_sphere.html

http://www.cascaeducation.ca/CSA/CSA_Astro9/files/multimedia/unit1/celestial_sphere/celestial_sphere.swf

http://astro.unl.edu/naap/motion3/animations/sunmotions.swf

http://www.astronomynotes.com/nakedeye/csph1t5.htm

http://www.astronomynotes.com/nakedeye/s4.htm

 

 

http://www.youtube.com/watch?v=8yCzzTkDSMo

Jack Horkheimer, for your interest.  Not related to the Celestial Sphere stuff.

 

 

Lab due in class.

FYI:

http://www.skyandtelescope.com/observing/home/168792986.html

Tentative field trip:  October 4, all day, DC

Lab 1

Lab 1 - Time and Space

In this lab, you will investigate the myriad ways of keeping time in the universe. Measuring the passing of astronomical time is by no means a trivial task - keep that in mind, as you find the current time according to various websites. This lab is structured as a series of topics, followed by questions and suggested websites. Have fun, and take your time! (Yes, it was time for that pun. On second thought…..)

Local Time

Give the current local time (whenever you are performing this lab), either EST or EDT. Specify whether or not we are on EDT, and when (and how) this will change.

Interested in the time elsewhere? Try this:

http://www.timeanddate.com/worldclock/ 

Universal Time

UT is counted from 0 hours at midnight, with unit of duration the mean solar day, defined to be as uniform as possible despite variations in the rotation of the Earth. Find the current UT. The clock applet below may be helpful:

http://tycho.usno.navy.mil/utclock.html

UT is very similar to Greenwich Mean Time (GMT), though this term is not used often these days. Both are 5 hours ahead of EST. Is this currently true? If not, why not?

Longitude and Latitude

These quantities give the location on the surface of the semi-spherical Earth, by laying a grid atop it. Lines of longitude are measured with respect to the Prime Meridian. Find the longitude of your hometown: Lines of latitude are measured with respect to the equator. Find the latitude of your hometown. 

Julian Date (JD)

Julian Day Number is a count of days elapsed since Greenwich mean noon on 1 January 4713 B.C., Julian proleptic calendar. The Julian Date is the Julian day number followed by the fraction of the day elapsed since the preceding noon.

Find the current JD:

Calendar

Which calendar do we currently use?

What calendar was this switched from, and when?

Why was the switch made?

Does all the world use the calendar we do? Explain.

Sidereal Time

ST is time based on duration of the Earth's rotation with respect to a point nearly fixed relative to the stars. Local Sidereal Time (LST) is computed from ST using a longitude correction. Find the current LST.

The Lunar and Solar Cycles

Have a look at sunrisesunset.com. Determine how the sunrise and sunset times change from day to day. Also determine how the moonrise and moonset times change daily. 

Etcetera

Discuss any other times and/or calendars that are of interest to you. 

Also, give a general conclusion (paragraph or more) about things that were interesting to you in this activity.