The Nearest Stars

Goals: To understand the distance scale between the Solar System, Oort cloud, and the nearest stars.

Before starting, turn on: stars, constel, mwVis, 1lmo, 1ly

You will be using: oort, 1ly, 10ly, jump command

Let's continue exploring the solar neighborhood from the previous tutorial. If you're starting a new session in the Milky Way Atlas, be sure to turn on the data groups listed above and use the jump command

jump 0.05 0.6 0.3 -60 10 170

to go to (x, y, z) = (0.05, 0.6, 0.3)pc with the viewing angles (R_x, R_y, R_z) = (- 60, 10, 170)^o.

From this position, the star labels are a bit large. Decrease their size using the Labelsize Slider and orbit the Sun using the left mouse button in Orbit Flight Mode. Set it drifting and observe the constellation lines. A few of them appear as though they're being pulled in toward the Sun. Stars like Proxima, Sirius, Procyon, and, to a lesser extent, Vega.

The Oort Cloud Shows the Most Distant Parts of Our Solar System

Before we discover the nearby stars, let's look at the outermost reaches of the Solar System. When the planets were forming, the larger, outer planets likely swept the Solar System clean of smaller bodies like comets. These were ejected from the inner regions by the strong gravitational influence of the planets, relegating the comets to an area called the Oort cloud. This “cloud” is where the comets have settled, and it ranges from 20,000 AU to about 100,000 AU (recall that 1 AU = 149 million km = 93 million miles and is the average Earth-Sun distance).

Turn on the Oort cloud. It's a wire-frame sphere, but how far does it extend? Because the highest concentration of comets lies around 50,000 AU, we place the sphere at this distance. While the Oort cloud is not a perfect sphere, we use the sphere as a representational model that provides us with the size and scale of the cloud. If you still have the 1-light-year grid on, you will notice that 50,000 AU equals about 10.5 light-months. Remember, the planets are lost in the glare of the Sun; Neptune is a little more than 4 light-hours away.

The Nearest Stars Are More Than Four Light-Years Away

Pull away from the Oort cloud and turn on the 10-light-year grid , increasing the star labels as necessary. Now the cloud is a small sphere and the nearby stars are beginning to reveal themselves. Try to approximate their distances.

In the Graphics Window, type the keys ‘cw.’ This resets the camera location, transporting you to a location that is 3 units up the + z-axis looking back toward the origin. Now back straight out from this position. By resetting the camera, you can be sure that you're looking at the grid face-on from a position perpendicular to the plane. Can you see the nearest star? Orbit a bit to regain some depth.

Proxima Centauri Is the Closest Star

Proxima is the closest star to the Sun. Aptly named, this star lies close to the Galactic plane too, allowing you to read off its distance from the 10-light-year grid (10ly). From here, it looks to be about 4.5 light-years away (it's actually 4.4 light-years from the Sun). Now see if you can maneuver yourself so that you're looking at Sirius and Procyon edge-on to the grid. Sirius will be on one side, Procyon on the other. See how far from the plane these stars are. Place your mouse on top of Sirius and either press the middle mouse button or type the ‘p’ key. Partiview should report back to you one of the following:

# [g1]Picked -1.7693 -1.9125 -0.4074 @2.86269 (of 32) "Sirius"

# [g1]Picked -1.7693 -1.9125 -0.4074 "HIP32349 HD48915 Gli244a Alp CMa Sirius" @2.86269 (of 30); colorb_v 0.021 lum 20.3348 absmag 1.45 appmag -1.44 txno 1 dist 8.6 dcalc 2 plx 379.21 hipno 32349

The first is a report of the label, located at (x, y, z) = (- 1.7693, - 1.9125, - 0.4074) parsecs. The ‘2.86269’ is the distance from which we are viewing the chosen object (your distance will likely be different). In the second report, Partiview reports from the stellar data set, printing the location information, names, and all the parameters defined in the data file, such as the star's luminosity, its absolute and apparent magnitude, and other information found in the speck file.

We want to know how far off the plane of the Galaxy, and hence the grids, the star is. The Milky Way Atlas is a Cartesian coordinate system expressed in x, y, and z parsecs. The x axis points toward Galactic center; the y axis is in the direction of Deneb, which is the direction of our rotation around the Galaxy; and z points perpendicular to the plane. So Sirius is 0.4074 parsecs from the Galactic plane, or (0.4074 pc)x(3.26 ly/pc) = 1.328 light-years. From above, Sirius appears to be about 9-10 light-years away (it's actually 8.6 light-years away).

Now move on to the next tutorial, in which we discuss other planetary systems outside the Solar System.

Digital Universe Atlas

Digital Universe Guide

The Nearest Stars