Watching the Dip: Transit Photometry Method Quiz

If a planet passes directly between its host star and an observer on Earth, then it will physically block a small fraction of the star's light; if we measure this brightness over time, then the resulting periodic "dip" reveals the planet's presence.

If a planet's orbit is tilted so that it never passes between the star and Earth, then it will never block the star's light from our perspective; if no light is blocked, then no transit can be observed.

If the planet and star are viewed as circular disks, then the amount of light blocked is proportional to the area of the planet (pi * Rp^2) divided by the area of the star (pi * Rs^2); if the pi symbols cancel out, then the transit depth equals the square of the ratio of their radii.

If we are plotting the intensity of starlight (flux) on the y-axis against time on the x-axis, then the resulting visual representation of the data is defined as a light curve.

If we see repeating dips, we find the period; if we measure the dip depth, we find the radius; if we analyze the shape of the dip, we find the tilt (inclination). If mass requires a gravitational measurement like radial velocity, then it cannot be found by photometry alone.

If a planet is large, then it blocks more light and creates a signal easier to distinguish from noise; if it is in a tight orbit, then the probability of alignment is higher and the transits happen more often, making them easier to catch.

If density is mass divided by volume, and if the transit method only provides the radius (volume), then we still lack the mass; if we do not have the mass from another method, then density cannot be calculated.

If NASA launched a mission to stare at a single patch of the Milky Way to monitor 150,000 stars for periodic dimming, then that mission was the Kepler Space Telescope.

If two stars orbit each other and one passes in front of the other, then the total light will dip; if the secondary star is very small or the eclipse is grazing, then the light curve dip may look identical to a planetary transit.

If TESS and CoRoT were built for wide-field transit surveys and JWST is used for high-precision follow-up transits, then they are valid tools; if Voyager and Cassini were deep-space probes for our solar system, they do not find exoplanets via transits.

If a planet is moving slower or is further from the star, then it will take more time to cross the star's disk; if we measure the time it takes to enter and exit the transit, then we can calculate its orbital velocity and semi-major axis.

If starlight passes through the thin layer of gas surrounding a planet during a transit, then specific wavelengths are absorbed; if we compare the light curve at different wavelengths, then we can identify chemicals in the planet's air.

If the ratio of the radii is 0.1 / 1.0 = 0.1, and if the depth is the square of that ratio, then 0.1^2 equals 0.01; if 0.01 is converted to a percentage, then the transit depth is 1%.

If we are defining the phases of a transit, and if the planet is entering the star's disk, then the start of the event is known as ingress.

If a star is a sphere of gas, we see deeper into hotter layers at the center than at the edges; if the edges look cooler and dimmer, then the planet blocks less light at the start and end of the transit, causing a curved (U-shaped) dip.

If a planet takes 12 years to orbit, then transits only happen once every 12 years; if a mission only lasts 4 years, it might miss the repeat; if the planet is far from the star, the chance of a perfect edge-on alignment is statistically much smaller.

If we compare the databases from Kepler, TESS, and ground surveys, then the transit method has confirmed thousands of planets; if this number exceeds that of the radial velocity or direct imaging methods, then it is the most successful.

If a planet's gravity from an unseen neighbor pulls on the transiting planet, then it will arrive at the transit point slightly early or late; if we measure these changes in the schedule, they are called Transit Timing Variations.

If a star's light naturally flickers or the telescope has electronic errors, then that "noise" can hide a planet; if the dip (signal) is much larger than those fluctuations, then the SNR is high and the planet is easily detected.

If the formula for transit probability is (Rs + Rp) / a (where a is distance), then increasing the size of the star or decreasing the distance to the planet increases the range of angles where a transit is visible from Earth.