-CelSphLab (1)
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Georgia State University *
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Course
1010
Subject
Astronomy
Date
Feb 20, 2024
Type
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9
Uploaded by HighnessCloverLapwing39
1 The Celestial Sphere ASTR 1010 Name: Overview In this activity you will implement what you know about the celestial sphere and celestial coordinates to locate the Sun, stars, and planets in the sky. You will also explore how the positions of these bodies change throughout the year. Objectives After completing this activity students will be able to: •
Identify the locations of the celestial poles, equator, and ecliptic. •
Use a celestial sphere simulator to find the Sun’s position along the ecliptic for any day of the year •
Use a celestial sphere simulator to observe the changes in the sun’s altitude and duration of time in the sky at different times of the year •
Use an astronomical database and coordinates to locate and name bright stars •
Use a celestial sphere simulator to observe bright stars and planets in the current night sky Definitions Here are some terms from lecture that we will be using today in lab: •
Celestial sphere
–
an imaginary sphere of infinite radius on which we imagine all the stars to be attached. As this sphere appears to rotate from east to west, it carries all the stars and constellations with it. The vernal (spring) equinox is at the origin of this system (RA= 00h 00m 00s, Dec = 00 00’ 00”).
•
Right Ascension (RA)
–
the east-west celestial coordinate (equivalent to longitude). RA is measured in units of time: hour (h), minutes (m), and seconds (s). •
Declination (Dec)
–
the north-south celestial coordinate (equivalent to latitude). Dec is measured in angular units of degrees, arcminutes (‘), and
arcseconds (
“). The celestial equator has a declination of 0°, the north celestial pole has a declination of +90°, and the south celestial pole has a declination of -90°.
2 •
Ecliptic
–
the Sun's apparent path through the sky. Intersects the celestial equator twice per year at RA= 0h0m0s and RA=12h0m0s. •
Constellation –
a region of the sky, bordered by arcs of right ascension and declination. Together, 88 constellations cover the entire celestial sphere, with their boundaries adopted officially by the International Astronomical Union in 1928. •
Circumpolar star/constellation
–
a star/constellation that never sets below the horizon due to its apparent proximity to one of the celestial poles. Part 1. Location, location, location! Match letter to corresponding location: Celestial Equator Ecliptic Celestial North Pole Celestial South Pole
1.
Define the ecliptic. What objects travel through the ecliptic? 2.
Why are the celestial equator and ecliptic offset from each other?
3 Part 2. The Sun’s Journey
For this section you will be using the Motions of the Sun simulator from astro-simulations. The simulator can be found here: https://ccnmtl.github.io/astro-simulations/sun-motion-simulator/ Once the applet has loaded, set your location to Atlanta by changing the observer’s latitude to 33.8° N
. In the General Settings (bottom right), make sure the boxes for the sun’s declination circle, the ecliptic, underside of celestial sphere, stick figure and shadow, and time of day are checked. You can change the location of the Sun by clicking and dragging the Sun on the celestial sphere diagram. To begin, change the date in the simulator to find the Sun’s right ascension and declination at the equinoxes, solstices, and today. You will find the RA and DEC values on the bottom of the screen towards the left-hand side. Complete the Table A: Table A. Location of the Sun Date RA (hrs:mins) Dec (degrees) March 21 June 21 September 21 December 21 Today’s Date: Part 2 Questions Choose a date in July and a date in December (any date in those months). Record your choices and the declination of the Sun on those dates. 3.
July date:
July declination: 4.
December date:
December declination: 5.
How does the declination of the Sun in July compare to the declination in December?
Why do you think that is? (Hint. Consider tilt of the Earth during these months/season.)
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4 For the two dates in July and December you chose, compare the amount of time the Sun spends in the sky. Set the simulator to your July date and drag the Sun so it is just peaking above the eastern horizon to imitate sunrise. Record the time below. Now drag the Sun across the sky so it is just below the western horizon. This will imitate sunset. Record the time below. Change to your December date and repeat. 6.
July sunrise time: July sunset time: 7.
December sunrise time: December sunset time: Note.
You may need to rotate (click and drag) the celestial sphere to move Sun from one edge of the sphere to the other 8.
In which month does the Sun spend the most time above the horizon and why? (Hint. Consider the tilt of the Earth during that month/season) Change the latitude to 90 degrees N (the latitude of the North Pole). For your July and December dates, record the declinations of the Sun at the North Pole on those dates: 9.
July declination at North Pole: 10.
December declination at North Pole: 11.
What is the difference in the declination of the Sun at this latitude compared to the latitude of Atlanta? (Hint. Does declination change based on latitude or are they separate measurements?) Set the simulator to your chosen July date. Set the time to midnight (00:00 –
24hr time).
Under the animation controls menu, click ‘Start Animation’. Watch the Sun move through one day of animation. 12.
How much time does the Sun spend in the sky in July at the North Pole?
5 13.
Knowing what happens in July, what do you think you would observe if you repeated this for the December date? Part 3. Star Finding For this section you will be using ‘Coordinate Query’ task from the astronomical database SIMBAD, which can be found at the here: http://simbad.u-strasbg.fr/simbad/sim-fcoo Using this database, copy and paste the RA (given in hours:minutes:seconds format) and Dec (given in degrees:arcminutes:arcseconds format) given in Table B to find 10 bright stars in the night sky! NOTE. Make sure you include the +/- on the declination values! Using screenshots, let’s do the first one together. Click the link above to open the ‘Coordinate Query’ task in SIMBAD. Copy the coordinates for Star 1 and paste them into the ‘Coordinates’ textbox (circled in blue) and press ‘submit query’ (circled in red):
Once you submit your query, if the star has other objects near it, your query might look like this:
6 If your query turns up multiple objects, check the RA and DEC against the value you have from the table
. Using this example, the RA values both round to 6:46:09, but the DEC value (-16:42:58.01) for the first object is a much closer match to the Dec value in the table, so ‘
alf CMa
’
(in the red square) is the object you would click on. After clicking on the object, you will come to a screen that has basic data and an image of the st
ar. Scroll down the page to the ‘Identifiers’ section, which will look like this:
Look for the identifier labeled “NAME”. Looking in this screenshot, the name of Star 1 is ‘Sirius’. Record the name in Table B and repeat this process for the remaining stars in the table. If your star has multiple names and you aren’t sure which one to choose, record them all!
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7 Table B. Positions of Ten Bright Stars Star RA (hrs:mins:sec) Dec (° : ’ : ’’
) Star Name 1 06:45:09 -16:42:58 2 07:39:18 +05:13:30 3 20:41:26 +45:16:49 4 19:50:47 +08:52:06 5 05:16:41 +45:59:53 6 05:14:32 - 08:12:06 7 14:15:40 +19:10:57 8 05:55:10 +07:24:25 9 16:29:24 -26:25:55 10 18:36:56 +38:47:01 Part 4. Tonight’s Sky
For this section you will be using the Stellarium Web Online Star Map. The simulator can be found here: https://stellarium-web.org/ To get Stellarium ready to go: •
At the top left corner, click on ‘View Settings,’ then make sure that ‘Ecliptic
•
Line’ is checked. •
Click the 3 horizontal lines on the top left corner of the screen to close the left-hand menu. •
Click on the ‘Atmosphere’ option to stop the Sun from blocking out stars.
•
Click on the ‘Constellations’ option to draw and label the constellations. •
Click on the location box (bottom left) to make sure it is set to in or near Atlanta. •
Click the clock (bottom right) to set it for tonight at 21:00 (9:00 pm in 24-hr time). With your simulator set up, let’s see what’s up in the current night sky
starting with planets! The word planet comes from the Greek word planḗtēs, which means wanderer. Due to their wandering nature, unlike the stars from the previous section, they are constantly moving to new coordinates. The brightest planets (visible to the unaided eye) will appear on the celestial sphere. So, using your eyes and maybe needing to click and drag around the sphere, answer the following questions:
8 14.
What planets are currently visible in the night sky? 15.
What celestial sphere feature do the planets follow along? Above the horizon, the crosshair on the equatorial grid marks the north celestial pole (NCP). Click on the clock (bottom left) and drag the circle along the moonlight bar. You should have noticed the stars very near the NCP moving in a circle around the pole and as you move time, they do not set below the horizon. These are circumpolar stars
, which will always be visible from that particular location on the Earth. Of course, the number of circumpolar stars is dependent on your latitude. If you are visiting the North Pole, then all the stars visible to you will be circumpolar. 16.
List some of the circumpolar constellations visible from Atlanta: Now rotate your view upwards until the horizon completely surrounds the outer edges of your screen. Click off the ‘Equatorial grid’ and click on ‘Azimuthal grid’. NOTE. Be sure to set your time back to 21:00 (9pm)! Constellations/ stars seen at the crosshairs of the Azimuthal grid are at zenith, directly overhead. Also familiarize yourself with the cardinal directions of the simulator (indicated by N, S, E, W located on the horizon) and answer the following:
17.
Name a constellation which is: a.
On the zenith: b.
Rising on the eastern horizon: c.
Setting on the western horizon: Note
. Rising/setting on eastern/western horizon means name a constellation that is near the eastern or western horizon (marked with E or W, circled in blue). Don’t use this screen capture to name your constellations because it isn’t set for the correct time!
9 18.
Click on the clock (bottom left) and drag the circle along the moonlight bar from sunset to sunrise. Name a constellation that is visible almost the entire night (excluding previously listed circumpolar constellations): Click on the clock (bottom left) and reset the time to 21:00 (9pm). Choose a bright star on the eastern horizon and click on it. Record the following details about your choice: 19.
Star name: Star RA: Star Dec: Clicking on the clock again, click the up arrow on the month portion of the date (Stellarium gives dates in YYYY-MM-
DD format). Watch how the star’s position changes as you keep the time of night the same but change the month. 20.
How is the star moving as you move from month-to-month? What causes this motion? To complete this assignment for grading: •
File Save As… Rename the file ‘YourLastName –
CelSphLab’
•
Upload the file to the ‘Celestial Sphere
Submission
’ assignment in in iCollege: Click ‘Add
Attachments’ Click ‘Upload’ Upload renamed saved file Click ‘Update’.
•
Consider the places at very north or very south latitudes (like the North Pole or the South Pole) that have 24 hours of sunlight during the summertime and 0 hours of sunlight during the winter and if you want to live in such a place.
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