Locate the star Betelgeuse and click on it. Information onBetelgeuse should appear in the top left of your screen. What isits azimuth and altitude?

Az (1 pt) = ________________
Alt (1 pt) = ________________

Now let’s switch to a different coordinate system. Press “E” orclick on the globe in your bottom menu bar to turn on some newcoordinates, and press “Z” or click on the radar icon (to the rightof the globe) in the menu bar to turn off the altitude and azimuthgrid.

This new grid should be tilted relative to the horizon. You arenow looking at the Right Ascension (RA) / Declination (DE)coordinate system. This system is very similar to longitude andlatitude on the Earth. If you look to the north, you will see thatthe lines converge near a moderately bright star. This is Polaris,the North Star. Its declination is +90 degrees, just like Earth’snorth pole has a latitude of +90 degrees. If we could see throughthe ground, the grid would converge again in the south atdeclination –90 degrees; this spot would be directly over theEarth’s south pole.

If you look at the RA/DE coordinates of Betelgeuse, you willnotice that RA is given in units of “h m s”. These stand for“hours”, “minutes” and “seconds”. There are 24 hours in one fullcircle (so each hour of RA is 15 degrees of angle), 60 minutes inone hour, and 60 seconds in one minute. (We astronomers have ournefarious reasons for using this arcane system, but it isn’timportant for now.)

What is the RA and DE of Betelgeuse (to the nearest degreeignoring arc mins and arc secs)?

RA (1 pt) = ________________
DE (1 pt) = ________________

For Betelgeuse, record both its Az/Alt coordinates and RA/DE in thetable below (record all values should be to the nearest degree,i.e., don’t include the arc mins and arc secs). Keeping the time at22:00, record the new positions for the dates specified. Note thateven when the star dips below your viewing horizon (alt < 0°),its position is still displayed. Continue to advance in four-monthincrements for an entire year (for time 22:00 at each date). (1point each totaling 16 pts)

Date   Az   Alt   RA  DE
2019-01-28        

     
2019-05-28             
2019-09-28             
2020-01-28             

Using the answers above answer the following:
Which coordinates change (1 pt)?
Which remain the same (1 pt)?
Do the changing coordinates ever come close to repeating (1pt)?
If so, after roughly how long (1pt)?

Next, keeping the time, date, and location the same, find Polaris.What is the altitude of Polaris to the nearest degree?

Let’s go somewhere else on the Earth. Open the Location Window (seepoint 1 at the start of the lab) and type “Greenwich” into thesearch box. Select the “Royal Observatory (Greenwich), UnitedKingdom” from the list. Change the date and time to 2019-01-27 at03:00PM (15:00) – this accounts for the 6-hour difference in timebetween Texas and England (your clock is showing Dallas time eventhough you changed positions).

Answer the following for Betelgeuse:
What are the Az/Alt (1pt)
What are the RA/DE? (1 pt)
Compare answers for a and b to the first row in your table for 3.Which numbers are different? (1 pt)
Which are the same? (1 pt)

Let’s say you are studying a new star and you need to get somepictures soon. You email all your friends who are at bigtelescopes, since it doesn’t matter from which telescope, nor whattime of night you get the pictures.
Should you send your friends the star’s current Az/Alt or itscurrent RA/DE? (1 pt)
Why? (1 pt)

What is the altitude of Polaris as seen from Greenwich (to thenearest degree)?

Polaris is used in navigation because of the fact that its altitudeis always the same as the latitude of the observer. Using youranswers for the altitude of Polaris from Dallas and Greenwich, howdo these values compare with the latitude of those locations?

Part III: Sunrise and Sunset

We all know that the sun rises in the east and sets in the west,right? Let’s examine the position and time of the rising andsetting sun over the course of the year, and see how true thatis.

Toggle back to Az/Alt coordinates (press Z) for this exercise,and return your location to Dallas, United States. (and make sureto check the enable daylight savings time in the location screen)Use the arrow keys to look toward the eastern horizon.

Set your date for 2019-01-21 and change the time until you seethe sun. Click on the sun to get its coordinates. Then change thetime of day until the sun has an altitude as close as you can to 0degrees, 0 arcminutes, and 0 arcseconds. Since its altitude iszero, this means that the sun is just starting to rise in the east.Get the altitude as close as you can, but because you cannot adjusttime in smaller than 1 second increments, understand that you willprobably not be able to get an altitude of precisely 0°0’0”. (Notethat with the online version of Stellarium, the coordinates do notupdate with each time change unless you re-select the Sun with eachtime change).

Find the sunrise and sunset times, and the positions to the nearestdegree, i.e., don’t include the arc mins and arc secs) on the datesspecified and fill in the table. Note to be sure to turn on thesetting to account for daylight savings time. (1 pt each, or 16total pts)

Date   Sunrise   Sunset
    Time   Az   Time  Az
2019-09-21              
2019-12-21             
2019-03-21             
2019-06-21             

What azimuth values correspond to precisely East and West?
East azimuth: _____________________ (1 pt)
West azimuth: _____________________ (1 pt)

Which dates does the sun rise/set on these azimuths?

On which day does the sun rise farthest to the north (smallestazimuth)? (1 pt)

Calculate the length of the day for each of the dates. Whichdate has the longest daytime?