The “Solar System Simulator”
The “Solar System Simulator” (http://space.jpl.nasa.gov) displays the locations of the planets (and many minor objects) for any date and time from 1990 – 2025. The simulator also renders planets and moons so you can see what they would look like with a high powered space-based telescope better than Hubble! A description of inputs you will use in this lab is given below.
A – Object you want to view
B – Location of Observer
C – Date and Time to display (remember UTC is seven hours ahead of PST at the moment)
D – Field of View Setting (1 degree = 60 arc min = 3600 arc sec)
E – Additional Options (I recommend you TURN OFF “show all spacecraft”
F – “Run Simulator” button
Exercise 1: Field of View. In order to understand the apparent size of far away astronomical objects, we will first determine the apparent size of our closest neighbor, the Moon. Set the solar system simulator to show you the Moon (A), as seen from the Earth (B), on Feb 16 in the year 2022 at 16:57 UTC (C). This is the next full Moon.
1. Vary the field of view (D) until the Moon just fills the screen. (The Moon may be just bigger than the edges of the box.) What field of view (in degrees) best represents the apparent diameter of the Moon? Coincidentally, the Sun has an apparent diameter nearly the same as the Moon, so we periodically witness “total” solar eclipses. Right now, the Moon is moving gradually away from the Earth, so that in the future, total eclipses will no longer occur on Earth! If you want a “rule of thumb” for the current size of the Moon (and Sun) in the sky, extend your arm and stick out your thumb – that’s about the right diameter.
Exercise 2: Orbits. Earth orbits the Sun more closely and more quickly than Mars (Earth year = 365.25 days; Mars year = 686.98 days). As such, there is a time approximately every two years when Earth and Mars are closest. At this point, Mars and Earth are in an orbital relationship called opposition. When they are farthest apart (on opposite sides of the sun) Mars is in conjunction (with the sun) when viewed from Earth. In this exercise we will use the simulator to view the orbital arrangement of Earth and Mars at various dates.
1. First, configure the simulator to show you the Solar System (A), as seen from above (B), on Jan 20 in the year 2022 at 18:00 UTC (C) – that’s pretty much right now. You will need to set the field of view to 5 degrees (D) to show the entire orbit of Mars (ignore Venus and Mercury for this exercise). Use Google Docs to create a chart like the one below and fill in the date and position of the planets. Today Date Orbits Sketch Distance (millions of km) Size (” arc) Next Opposition Next Conjunction 12/8/22 11/17/23
2. Change the simulator to view Mars from Earth and field of view to 0.01 degrees. Sketch the planet (only relative size, and the illumination pattern are necessary) and record the distance (millions of km) and apparent size (arc seconds) below.
3. Repeat these steps for the next conjunction (11/17/23) and opposition (12/8/22), then upload your finished chart here. 2) Use the simulator to view Venus from Earth. By varying the date, find as many of the phases as you can. (a) For each phase, record whether it was found and the date. (b) What phases (if any) were not found? Why?
Exercise 4: A Martian Day. In lecture, it was mentioned that Mars has a nearly Earth-like day (Mars rotational period is around 24 hours). Here we will use the simulator to estimate the length of the martian day.
1) Set the simulator date to a random date and time, and display the view of Mars from Earth. Adjust the field of view so Mars fills the screen. Identify a major feature (e.g., a dark or bright patch) and remember its location. What date and time did you choose?
2) Advance the simulator in time by 1 Earth-day. What is the location of the feature relative to the previous day? Is the Martian day shorter or longer than an Earth day?
3) Now adjust the time such that the feature is in the same position as your starting day and time. This will likely take multiple attempts. What is your best estimate for the length of the Martian day?
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