Astro 7n

Art Project 2 Instructions To get started:

While keeping this Instructions page open, go ahead and open up a second browser window or tab, for the "Art Project 2 Lab Journal" quiz/form.

You will be collecting information about a known extrasolar planet and its host star in "Phase 1" that needs to be recorded near the top of that form. Further down, you will fill in some more details and answer a few questions as you complete that and "Phase 2," and then answer some more questions based on your experience in "Phase 3."

Unlike in Art Project 1, where the different project phases had different due dates, here you can do the whole thing all at once. Having the "Lab Journal" quiz/form already open as you read and work down through these Instructions should help smooth out the process overall.

Let us get started with...

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Phase 1 — Find a Planet!

For this portion of the project we will use the "NASA's Eyes" app — available either online to run in your web browser, or as a free downloadable stand-alone program, at the following links:

 in-browser version: https://exoplanets.nasa.gov/eyes-on-exoplanets/ (链接 到外部网站。)

 stand-alone app: https://eyes.nasa.gov/ (链接到外部网站。)

The two versions present the same general information, although the formatting is slightly different. The performance (speed / smoothness) and visual quality is generally better in the stand-alone program, although the web-based version has the advantage of not needing to deal with downloading and installing a new piece of software on your computer. You may use either for this project.

If you decide to get the stand-alone app version, note that it has several "modes" — all of which are cool, of course — but for this project we will specifically be using the "Eyes on Exoplanets" one (open the app, and choose "Eyes on Exoplanets," on the far right side of the main menu screen; there may be a little pop-up that asks whether to use the app in full-screen mode or not, and it does not matter which you choose).

A short introductory sequence will play, showing an overview of the data set of stars in the Sun's neighborhood, and which of those have been identified as having planets.

After the introduction plays through, you can click-and-drag to move the view around, and look around at the stars that have had planets detected around them (the stars with 8-pointed star icons, instead of just tiny dots). You can scroll up or down to zoom in and out (or use the slider on the far right side of the window in the stand-alone app).

Depending on how closely zoomed in on the Sun, or how far outward you are looking from, you may notice a couple of distinct "ray-shaped" or clustered regions of the galaxy in which a large number of planets have been detected around stars in those directions. These are data sets from specific dedicated planet-detection surveys — including, especially, the Kepler mission you learned about in Unit 3 of the astronomy video game. There is nothing necessarily "special" about those specific directions in the galaxy that suggests there are more planets formed around stars there; it is simply a result of the planet detection surveys concentrating their observations in those directions. One could imagine the formation of planets around stars in any given other direction as well — although as you learn in Unit 4, there are vastly more stars within the disk plane of our Milky Way galaxy than outside of it.

You can hover your mouse over any of these stars to see the star's name (or catalog entry number, in a lot of cases), how many planets have so far been discovered around it, and how far that star is from our Solar System.

There are a great many to choose from. NASA's Eyes also has a certain few they highlight of particular interest; if you are using the web-browser-based version of it, then you can click "Browse Planets" at the top right to look over

some; if you are using the downloaded version, try clicking the little spark-outlined "!" icon along the middle of the top of the window.

Click on a star to zoom in on it.

TIP: Especially if you are using the downloaded stand-alone version of NASA's Eyes, you may want to go ahead at this point and write down the name of the star you clicked on, since that program will occasionally reset itself back to the initial "start up" view, or enter a "highlights / tour" mode on its own, if left idle for a few minutes. You can prevent this by just interacting with the star or planet, clicking a button, etc. now and then to keep it focused on your chosen target.

Making a note at least of the name of a star you are interested in will help you quickly track it down again, later, using the Search function (magnifying glass icon, along the top) in either the app or in the web browser version.

You can enter this star name in the first question blank of the Art Project 2 Lab Journal.

You can click on the "Star" button in the lower right (if using the browser version — or the "Star View" button on the left in the stand-alone version) and, below that, see a comparison between your target star and our Sun; or for the stand-alone version, a pop-up window on the left will tell you a few things about the star itself.

That information on the star may include...

 Name o ... which may be a stellar catalog number entry in most cases. Recall that a great

majority of stars are fainter than those we can readily see with the naked eye from Earth.

 Distance from Earth o in light-years

 Visibility o whether this star is possibly visible to the naked eye, from Earth (depending, of course,

on the sky conditions at a given location on Earth)  Number of Planets

o note: this is just the number so far detected — not necessarily all of them that might be there! (further discussion on that point, below)

 Star Type o just like the spectral types we described in Unit 3; i.e., "O B A F G K M"

 Magnitude

o This is a function of brightness, but on a logarithmic scale; a lower number on this scale means a brighter light source. Recall the "Inverse-Square Law," and that we can derive an estimate of the star's actual luminosity (relative to our Sun's) if we also have an estimate of its distance from us (which NASA's Eyesalso provides).

o The web version of NASA's Eyes does not show this information, or in some cases it may not be well defined or known, but you can take a look at the video game's companion "Encyclopedia" page on Stellar Mass (链接到外部网站。) for an idea of what the star's luminosity (not brightness) may be, based on type.

 Mass o relative to our Sun's o The web version of NASA's Eyes does not show this information, or in some cases it

may not be known, but you can take a look at the video game's companion "Encyclopedia" page on Stellar Mass (链接到外部网站。)for an idea of what the star's mass may be, based on type.

You can zoom out by scrolling to get away from the star close-up and see the planet(s) orbiting around it; alternatively, in the web version click the "System" button in the lower-right corner, or the "Planetary System View" button on the left in the stand-alone app.

In the stand-alone program, to slow down the rate at which the planets are shown moving in their displayed orbits, use the slider at the center/bottom of the window. If you slide the slider bar to the center, it will pause; alternatively, you can click the "real rate" button and it should nearly stop the planet motion. This makes it much easier to click on an individual planet to view its information, later.

You can click "Compare with our Solar System" (lower-right in the web version, or middle of the left side in the stand-alone version) to see about how large the planet(s) orbits are estimated to be, compared to the orbital distances of our Solar System's planets about the Sun. For the great many of these stars which are lower mass than our Sun, you may be surprised at first at just how close many planets orbit — multiple planets within the orbit of Mercury, for instance. Some of the reasons for this being a common observation — not so surprisingly, in retrospect — are described in more detail, below.

You can also click the "Habitable Zone" button to see a blue-shaded region around the star that estimates the range of orbital distances which may allow for liquid water on a planet's surface, should it orbit within that region. This is based on a pretty simple calculation that does not include some factors that

may contribute to this region being larger or smaller. For instance, our planet Earth might well be a little too cold for liquid water if it were not for having an atmosphere to help retain heat at the surface via the "greenhouse effect"; on the other hand, Venus' "runaway greenhouse effect" has rendered what might otherwise have been a habitable planet into a super-hot wasteland.

The roughly-estimated habitable zone overlay may not necessarily display for all stars, since it depends on having sufficient data on the star to make those calculations.

Click on a planet to view some information on it, which may include...

 Name  Planet type

o Bear in mind that this is a "first guess" based on the limited physical characteristics we can measure, combined with some comparison to planets in our Solar System.

o Some of these "nicknames" for planet types — "Hot Jupiter," "Neptune-like," "Super Earth," etc. — just come from best guesses based on the specifics of the star & planet, and comparisons to what we have in our Solar System. A "hot Jupiter," for instance, is something that may be Jupiter-sized (or even bigger) that is closer to the star than Jupiter is to our Sun. A "Super Earth" might be something that is ... sort of around Earth-sized — a little bigger, but quite so large as to enter into the class of a gas giant or "Neptune"-like. A rocky planet, of course, is probably just a rocky planet — perhaps like Mercury, or Earth's Moon, but could still also be something like Mars or Venus, or... even Earth (in absence of knowledge about an atmosphere). Again the point is: the "planet type" given here is kind of an initial guess, and not necessarily any sure thing.

 Discovery Date  Planet's Mass, if known (may be an estimate)

o May be expressed in numbers of Earth or Jupiter masses (recall that Jupiter's mass is

about 318 × Earth's)  Planet's Radius, if known (may be an estimate)

o May be expressed in numbers of Earth or Jupiter radii (recall that Jupiter's radius is

about 11 × Earth's)  Orbital radius

o Expressed in Astronomical Units ("AU")  Orbital period

o In hours, Earth days, or Earth years, etc.  Eccentricity

o Recall that this is a measure of how elongated (elliptical) the planet's orbit is; a value of 0 corresponds to a circular orbit, and gets closer to 1 the more elongated it is (like we see for comets, but also for some planets in other star systems)

 Method of detection o Usually either "radial velocity" or "transit," although a growing number are found

through "micro-lensing" as well

You may search around in NASA's Eyes for as long as you like, until you find a planet you find interesting. For this project you are not required to find a specific planet, or a star or planet of any particular type. NASA's Eyes updates every so often with a few "featured" planets (look for the "Browse Planets" option at the top of the web version, or in the stand-alone app try clicking either the telescope dome icon for "latest discoveries" or the exclamation-point/spark icon for "extreme planets" and then one of the numbers that appears along the bottom of the window).

Once you have found a star and a planet that you want to work with further, then go to the "Art Project 2 Lab Journal" quiz/form page (again, probably most convenient if this were opened at the start and then kept open in another window or tab throughout your work on this project). Fill in the upper portions of it (the "Phase 1" section) with all the information gathered from NASA's Eyes.

There are also a couple of short essay-type questions at the end of this section, that should only take a couple minutes to fill in. You can use these spaces to note what motivated or inspired your selections of a particular star and planet in NASA's Eyes here in "Phase 1."

Next: Let us pause, here, to review some of the relevant science involved in all this ...

1. What can we tell (or begin to guess) about a star or planet, based on just a couple measurements like a spectrum, or seeing a periodic partial drop in brightness or a little wobble?