By pure coincidence, for next few years the orbit of the satellite Namaka around the dwarf planet Haumea is nearly edge-on to our line-of-sight. This type of configuration does not last for long, because as Haumea travels around the sun in its 283 year orbit, we will continuously see the Haumean system from different angles. It is only edge-on at the angle we see right now, and at the angle it will again be in 141 years -- half of a Haumean year from now.
In addition to being an interesting coincidence, the fact that the orbit of Namaka is nearly edge-on provides the opportunity for gaining an enormous amount of information about the Haumean system. Over the course of Namaka's 19-day orbit around Haumea, Namaka will pass in front of and behind Haumea, temporarily disappearing. While the Haumean system is so far away that we will never be able to directly watch these disappearances, we will be able to notice that when Namaka disappears behind Haumea, for example, the total amount of light from the system will go down by a small amount. When Haumea reappears the total amount of light will go back up.
Measurements of the precise timing of these events will allow us to measure properties of Haumea and its system to staggering accuracy. For example, the size of Haumea is currently uncertain by perhaps 200-300 km. If we can measure precisely when an event occurs, we get a measurement of the location of the limb of Haumea (and thus the size of Haumea) to an accuracy of perhaps 20 km. By measuring many of these events that traverse slightly different chords across Haumea, we will be able to derive a highly accurate shape of this very unusual dwarf planet.
The measurements are not going to be easy. Haumea is an 18th magnitude object. Namaka disappearance will change the total amount of light by around 1%. We suspect that good measurements will require a telescope ~2 meters in size or larger, sadly putting the events out of the range of almost every amateur telescope on the planet. In addition to being faint, Haumea is rapidly rotating, so the total amount of light from the system is already changing by 25% over a 2 hour period. Careful measurement of the normal variability of Haumea will also be important.
Despite these difficulties, we are attempting to organize an international consortium to observe as many of these mutual events as possible. Only with a large number of detections of different events will the data truly live up to its potential.
The pages and plots below are designed to help in the planning for the consortium and for anyone else who wants attempt these measurments on their own; we encourage as many people to try as possible!
There are five main types of events that will be occuring over the next few years. These are illustrated here:
When Namaka is behind Haumea, it can be eclipse by Haumea's shadow, occultated by Haumea itself, or a combination. In all cases, Namaka will simply disappear and the key measurement will be the timing of the disappearance.
When Namaka is in front of Haumea, it can transit across Haumea, and, if the geometry is right, its shadow can also transit. These events are particularly interesting. When Namaka is transiting it doesn't simply disappear, it covers up part of Haumea. If Haumea and Namaka had surfaces of precisely the same brightness or albedo, the total amount of light would be just like Namaka were eclipsed. But we currently have no way to know anything about the albedo of the surface of Namaka. These measurements will very quickly give us this number, from which we will eventually be able to calculate the size and density of Namaka and determine the materials from which it is made. The transit of the shadow gives us similar information.
Not shown in the plot above are grazing events. These are events where Namaka is predicted to just barely transit or perhaps not quite transit (or be occulted or eclipsed). Verifying that there is indeed no event at these times (or discovering that there is indeed an event!) will be one of our best constraints on the width of Haumea, which is one of the least well known parameters.
The lists below show each set of events during the 2009 observing season. The times of ingress (beginning of the event) and egress (end of the event) are given. The most important measurement is the time of ingress and egress. It is not particularly important to observe both events from the same observatory; if your observatory can only see one or the other that is still extremely valuable.
Currently the uncertainty in the precise time of these events is approximately +/- 1 hour. As soon as a single event is positively detected, we will be able to refine these estimates with much more certainty. Note that while this uncertainty might make the earliest events, when Haumea is only observable for a limited amount of time from any location on the earth, difficult.
The plots below show the earth as viewed from Haumea at the time of each event. The daylit side of the earth is shown bright. If you can see your observatory on the nighttime side, your observatory can see Haumea! The dashed lines near the daylit side of the earth show the locations where the sun is 6 degrees, 12 degrees, and 18 degrees below the local horizon (also known as civil, nautical, and astronomical twilight). The concentric circles near the horizon show the location on the earth where Haumea is current seen at an airmass of 1.5 , or ~40 degrees above the horizon (the inner circle), an airmass of 2.0, or 30 degrees above the horizon (the middle circle) and and airmass of 2.5 or 23 degrees above the horizon (the outer circle, not counting the limb of the earth itself, at which location Haumea appears right at the horizon).
