## Astronomy C

idislikeboomi
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Posts: 9
Joined: January 19th, 2019, 4:07 pm

### Re: Astronomy C

Anyone feel like solving this problem: "Given that a Type Ia Supernova has a redshift of z = .47 and a peak absolute magnitude of -19.3, determine its
peak brightness as viewed from earth. Assume a Hubble’s Constant of ~70 km/s/Mpc" and telling me what you get? I keep getting an apparent magnitude 22.22 but the key for the test says 48-72, its from Fayetteville-Manlius btw.

pb5754[]
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Posts: 380
Joined: March 5th, 2017, 7:49 pm
Division: C
State: NJ

### Re: Astronomy C

Anyone feel like solving this problem: "Given that a Type Ia Supernova has a redshift of z = .47 and a peak absolute magnitude of -19.3, determine its
peak brightness as viewed from earth. Assume a Hubble’s Constant of ~70 km/s/Mpc" and telling me what you get? I keep getting an apparent magnitude 22.22 but the key for the test says 48-72, its from Fayetteville-Manlius btw.
That is also what I got, I believe you are supposed to use the redshift to find distance through Hubble's, then plug it into distance mod. This gives you m = 41.5-19.3 = 22.2. I think the key flipped their signs, since then 41.5+19.3 = 60.8

SentientJello
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Division: C
State: CA

### Re: Astronomy C

Has there been any firm confirmation of next year's topic? I've heard rumors that it may be Starburst Galaxies again or change to Star & Planet Formation, with Stellar Evolution as always, but I'm not certain on either.
Current Div C Competitor, Former OVMS Competitor
2016/2019/2020: Astronomy/Reach for the Stars, Dynamic Planet, Fossils
2018: Astronomy, Dynamic Planet, Fermi Questions
2017: Dynamic Planet, Reach for the Stars, Rocks and Minerals
SONT 2017 SoCal Div B Competitor

Name
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State: NY
Location: Syosset

### Re: Astronomy C

How do you do the last question on the MIT test? It asks for an upper/lower bound distance estimate in MPC, and your given a picture with the UBVI filters of the galaxy. U is not visable, and BVI is visable. From an earlier part of the question, it mentions the lyman limit at 91.2 nm. So any wavelength shorter then the lyman limit would've been redshifted to the lyman limit and absorbed. So the shortest wavelengths detected should've been emitted at the lyman limit- which is B filter. Using the online value of the B filter (wiki says 445 nm), redshifted from 91.2 you get about 17000 MPC, which is way to big.
Now using their answers (3650-4100 MPC) and solving for the detected photon wavelength implies that the 91.2 nm photons should've been shifted from 167 to 176 nm, well under even the U filter.
So what am I doing wrong?
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ethang137
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Joined: August 23rd, 2019, 6:38 pm

Hi, I'm still a little new to this area of physics and am looking for some help with a specific kind of problem.
I'm given a radial velocity curve for a binary system and asked to find the semi-major axis for this. I understand there's a relationship here but I can't seem to quite get it. Any help with an example would be extremely appreciated!! I've been stuck on it for a while now and after looking through a bunch of pages online I'm still at a loss :/

Unome
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Hi, I'm still a little new to this area of physics and am looking for some help with a specific kind of problem.
I'm given a radial velocity curve for a binary system and asked to find the semi-major axis for this. I understand there's a relationship here but I can't seem to quite get it. Any help with an example would be extremely appreciated!! I've been stuck on it for a while now and after looking through a bunch of pages online I'm still at a loss :/
Find the period of the curve from the graph. Assuming this is the standard (simplified) version, the peaks of the graph equal the orbital velocity. Take those and calculate the orbital circumference (multiply them), and go from their to the orbital radius (equals semi-major axis for a circular orbit, which is usually assumed for the sake of the problem).

A natural follow-up may be to use this semi-major axis with Kepler's Third Law.
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