Main Page
Welcome to the explain xkcd wiki!
We have an explanation for all 3290 xkcd comics, and only 41 (1.2%) are incomplete. Help us finish them!
Latest comic
| Antiques Roadshow |
 Title text: The family lore was that we've had it ever since it was ejected from a star-forming gas cloud, but it seems more likely that my great-grandparents probably just bought it while on vacation in the galactic thin disk. |
Explanation
This comic is a play of the TV show Antiques Roadshow, BBC and PBS series in which members of the public can have antiques assessed and valued by experts. Often there are two outcomes of the valuation: the item is a genuine antique of surprisingly high value, or the item is a modern replica and of a disappointingly low value. This comic extends this scenario by having a star appraised, an item that doesn't normally appear on the show.[citation needed]
In this comic, Cueball is having a star assessed. The star is not, as he had hoped, an old population III star, but a more recent population I star. Younger stars tend to have higher levels of iron, while Population III stars are composed almost entirely of hydrogen and helium. Cueball's comment "at least it has sentimental value" is similar to things people on the show say after learning that their "antique" is in fact a modern, low-value replica.
In cosmology, stellar population groups stars into three broad categories based on their chemical composition, which is correlated with when the stars formed during the history of the universe. Population III stars have never been directly observed. It is thought that they were very large, and formed out of gas that contained no heavy elements, such as iron. As they were large, they burned their fuel rapidly and exploded in supernovae, seeding the universe with the first elements heavier than hydrogen and helium. The direct observation of a population III star would be a major result in astronomy, and hence very valuable. Population I stars are much more common; all the stars visible in the sky, including the Sun, are population I stars.
The title text about "family lore" echoes other things that happen in Antiques Roadshow, with people who are having items assessed often having family stories about the items. The 'star-forming gas cloud' refers to clouds of gas and dust called molecular clouds that are the common birthplaces of stars. Stars can get ejected from them via a gravitational slingshot from other star(s). The "galactic thin disk" is a part of a spiral galaxy that has most of the galaxy's stars.
Transcript
[Ponytail and Cueball are standing on opposite sides of a small table. On the table is a small stand, and floating above it is a tiny, glowing star. Ponytail is pointing to the star. At the bottom left is the logo of the US version of Antiques Roadshow: a treasure chest with the top partly open and the initials "AR" on the front. Extending from that to the right is a ribbon saying "Antiques Roadshow".]
Ponytail: Now, your grandfather said this was a relic low-mass population III star, from the first generation of stars. Unfortunately, the high iron content shows that it formed much later, after several rounds of supernovas. I'm afraid it's a population I star.
Cueball: Aw, darn. Well, it still has sentimental value.
View comic discussionNew here?
You can read a brief introduction about this wiki at explain xkcd. Feel free to create an account and contribute to the wiki! We need explanations for xkcd comics, characters, What If? articles, and everything in between. If it is referenced in an xkcd comic, it should be here.
- If you're new to wiki editing, see the explain xkcd:Editor FAQ for a specific guidance to this wiki and the more general help on how to edit wiki pages. There's also a handy wikicode cheatsheet.
- Discussion about the wiki itself happens at the Community portal.
- You can browse the comics from the list of all comics or by navigating the category tree at Category:Comics.
- The incomplete explanations are listed here. Feel free to help out by expanding them!
Rules
Don't be a jerk!
There are a lot of comics that don't have set-in-stone explanations; feel free to put multiple interpretations in the wiki page for each comic.
If you want to talk about a specific comic, use its discussion page.
Please only submit material directly related to xkcd and, of course, only submit material that can legally be posted and freely edited. Off-topic or other inappropriate content is subject to removal or modification at admin discretion, and users who repeatedly post such content will be blocked.
If you need assistance from an admin, post a message to the Admin requests board.