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Home , Great Debate (astronomy)

Extra Credit: A Peer Panel Evaluation (up to +2% on final grade)

* You will need to decide which area of research you are focusing on and which telescope you are arguing for BY THE END OF THIS WEEK and let me know via a survey response (await email for this).

* you will need to have a first, complete draft done by END OF NEXT WEEK

* you will need to read a few others’ essays and offer a useful critique with a set of your peers, suggest improvements, and give a grade according to the rubric (you will need to schedule this outside of class and return comments to the proposers BY TUESDAY, NOVEMBER 29.

* your final essay is due DECEMBER 1 at the beginning of class. THE DRAKE EQUATION. ARE WE ALONE? ARE WE ALONE? How many sun-like stars (with planets) have a planet in the habitable zone?

Petigura et al. (2013) How many sun-like stars (with planets) have a planet in the habitable zone?

Petigura et al. (2013) We didn’t have any clue until Kepler came along, just a few years ago. The best current estimate is that 20+10% of all sun-like stars have planets in their habitable zones. The Kepler Orrery: the incredible diversity of planetary systems. Shout out to Dan Fabrycky! The Kepler Orrery: the incredible diversity of planetary systems. Shout out to Dan Fabrycky! Time to zoom WAYYYY out… Time to zoom WAYYYY out… To do that, we better know how to measure distances to things well. “We are probably nearing the limit of all we can know about astronomy.” -1888

Simon Newcomb “We are probably nearing the limit of all we can know about astronomy.” -1888 “Flight by machines heavier than air is unpractical and insignificant, if not utterly impossible.” -1902 Simon Newcomb We already know a few ways of measuring distances…

But that’s it so far! Or is it? We already know a few ways of measuring distances…

2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs. 1. We measured the distance to the sun using the transit of Venus!

But that’s it so far! Or is it? We already know a few ways of measuring distances…

2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs. 1. We measured the distance to the sun using the transit of Venus!

3. With technology we can actually use radar to measure distances to objects in our solar system (and verify the distance to the sun)…

But that’s it so far! Or is it? Recall the main sequence fitting technique for measuring distances?

A

B apparent magnitude apparent

color We already know a few ways of measuring distances… 2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs.

1. We measured the distance to the 4. Matching the Main-Sequence in sun using the transit of Venus! star clusters…

3. Radar (for the Solar System)

How far can that get us? We already know a few ways of measuring distances… 2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs.

1. We measured the distance to the 4. Matching the Main-Sequence in sun using the transit of Venus! star clusters…

3. Radar (for the Solar System)

How far can that get us? We already know a few ways of measuring distances…

2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs.

How far out do Parallax measurements take us? We already know a few ways of measuring distances…

2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs.

How far out do Parallax measurements take us? We already know a few ways of measuring distances…

2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs.

How far out do Parallax measurements take us? We already know a few ways of measuring distances…

2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs.

only a few hundred parsecs!

How far out do Parallax measurements take us? 1. Radar (for the Solar System) / geometry

3. Matching the Main-Sequence in star clusters…

4. Standard Candles! (Like Cepheid Variables) 2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs. 1. Radar (for the Solar System) / geometry

3. Matching the Main-Sequence in star clusters…

4. Standard Candles! (Like Cepheid Variables) 2. We used PARALLAX to measure the distances to the nearest stars…

but this is only good to a few hundred parsecs. The Cosmic Distance Ladder And the great Shapley/Curtis Debate. Charles Messier, created the astronomical catalog of 110 odd things he couldn’t explain, now called “Messier objects” (in 1771) which were basically not anything anyone could explain. Charles Messier, created the astronomical catalog of 110 odd things he couldn’t explain, now called “Messier objects” (in 1771) which were basically not anything anyone could explain. Charles Messier, created the astronomical catalog of 110 odd things he couldn’t explain, now called “Messier objects” (in 1771) which were basically not anything anyone could explain.

Fast forward ~140 years, everyone’s made great progress in understanding star systems (not planets really), but the HR diagram is figured out, basics of stellar temperatures, composition, and distances with parallax, but many of the Messier Objects were still a mystery… Henrietta Swan Leavitt She studied the variability of stars’ flux and deduced the “period-luminosity relationship”

Henrietta Swan Leavitt She studied the variability of stars’ flux and deduced the “period-luminosity relationship”

Henrietta Swan Leavitt She studied the variability of stars’ flux and deduced the “period-luminosity relationship”

Henrietta Swan Leavitt She studied the variability of stars’ flux and deduced the “period-luminosity relationship”

If she couldn’t make parallax measurements for these stars, so no distances, why is this not a period-flux relationship? How does she know it’s a period-luminosity relationship?

Henrietta Swan Leavitt She studied the variability of stars’ flux and deduced the “period-luminosity relationship”

If she couldn’t make parallax measurements for these stars, so no distances, why is this not a period-flux relationship? How does she know it’s a period-luminosity relationship?

Henrietta Swan Leavitt She studied the variability of stars’ flux and deduced the “period-luminosity relationship”

If she couldn’t make parallax measurements for these stars, so no distances, why is this not a period-flux relationship? How does she know it’s a period-luminosity relationship?

Henrietta Swan Leavitt

She didn’t know the distances! But she knew they were all at the same distance from the Earth, approximately. As long as they are the same distance away from us, a period-flux relationship is a period-luminosity relationship. She studied the variability of stars’ flux and deduced the “period-luminosity relationship”

If she couldn’t make parallax measurements for these stars, so no distances, why is this not a period-flux relationship? How does she know it’s a period-luminosity relationship?

Henrietta Swan Leavitt

She didn’t know the distances! But she knew they were all at the same distance from the Earth, approximately. As long as they are the same distance away from us, a period-flux relationship is a period-luminosity relationship.

Henrietta Swan Leavitt Harlow Shapley

Henrietta Swan Leavitt Stars

Cepheid Variable Stars are Standard Candles, Measures distance to star clusters, since we know their luminosity

If a Cepheid Variable A is twice as (a) 0.5 / fainter far away as Cepheid Variable B it (b) 0.5 / brighter will be ______times ______on (c) 2 / fainter the sky than Cepheid Variable B. (d) 2 / brighter (e) 4 / fainter (f) 4 / brighter Cepheid Variable Stars

Cepheid Variable Stars are Standard Candles, Measures distance to star clusters, galaxies since we know their luminosity

If a Cepheid Variable A is twice as (a) 0.5 / fainter far away as Cepheid Variable B it (b) 0.5 / brighter will be ______times ______on (c) 2 / fainter the sky than Cepheid Variable B. (d) 2 / brighter (e) 4 / fainter (f) 4 / brighter Harlow Shapley

Henrietta Swan Leavitt

Unaware of her death four years prior, the Swedish mathematician Gösta Mittag-Leffler considered nominating Henrietta Swan Leavitt for the 1926 Nobel Prize in Physics, and wrote to Shapley requesting more information on her work on Cepheid variables. Shapley replied, let Mittag-Leffler know that Leavitt had died, and suggested that the true credit belonged to his (Shapley's) interpretation of her findings. She was never nominated, because the Nobel Prize is not awarded posthumously. (He was never nominated either, though his grandson is a Nobel Laureate in Mathematics!) Harlow Shapley

Mapped the period-luminosity relationship for a few stars we actually knew the distances to from parallax! Those were another type of variable called RR Lyrae… Harlow Shapley

Mapped the period-luminosity relationship for a few stars we actually knew the distances to from parallax! Those were another type of variable called RR Lyrae… and used that to measure the characteristic distance scale of the ! Harlow Shapley

Due to the enormous size of the that he measured (he guessed 300,000 light years across) Shapley thought that spiral nebulae had to be stars forming (e.g. protoplanetary disks) inside of our own galaxy.

? = Heber Curtis Curtis thought Shapley was wrong: spiral nebulae were “island ” just like our own galaxy the Milky Way. He didn’t believe Shapley’s size measurements (thinking the MW was smaller) but showed that the spectrum of a spiral is similar to our own galaxy. ? = The “Great Debate” of 1920 The Scale of the Herber Curtis vs. Harlow Shapley

spiral nebulae are spiral nebulae are separate galaxies within the Milky Way

50000 ly 30000 ly 300000 ly 25000 ly

100000 ly 25000 ly

100000 ly

The right answer: a little of both!