How large would VY Canis Majoris appear from one light year away?

Question

Basically, would it appear as large or larger than the sun? What would it be comparable to?

Answer 1

VY Canis Majoris has a radius of around 2100 times that of the sun, ie. 1.46 x 10^12m, one light year is 9.46 x 10^15m, a quick bit of trig thus gives an apparent diameter of around 1 minute of arc. About the size of Venus at its closest.

Answer 2

If we assume that VY Canis Majoris is 2000 solar widths wide (i.e. 2000 times as wide as our own Sun)



5.8785E+12 miles in a light year divided by 2000 = 2,939,249,905 miles. This is about the distance from Neptune to the Sun which is 2.8 billion miles.



So from one light year away, VY would look about the same size at what our Sun does from Neptune, which would be much smaller than what we see it as from Earth. It would not be a point of light, you'd probably see some roundness to it. It would still be quite bright, but not as bright as on Earth.



Put another way, one light year is 39,295 AU. Divide by 2000 and you get 19.6 AU. Neptune is 30 AU away. So my math might not be quite right, but I agree it would probably be the size of Venus.

Answer 3

My source is a paper by Philip Massey et al 2006 ApJ 646 1203-1208, who believe that VY CMa has been overrated in regard to its size and luminosity, and underrated in regard to its effective temperature.



VY Canis Majoris

T = 3650 K

R = 600 solar radii = 4.176e11 meters

σ = 5.6704e-8 W m⁻² K⁻⁴

L = 4π σ R² T⁴ = 2.206e31 watts

L/Lsun = 57646

м = 4.75 − 2.5 log(L/Lsun) = −7.15



d = 1 light year = 9.4607e15 meters



Apparent angular diameter, D, of VY CMa from a distance of 1 light year.



D = 2 Arctan(R/d) ≈ 18 arc seconds



That's about the same angular size as Mars at a typical opposition.



Apparent magnitude, m, of VY CMa from a distance of 1 light year.

d₀ = 3.0856e17 meters

m = м + 5 log (d/d₀) = −14.7



It would be 7 times brighter than the full moon.

Answer 4

It is very likely that that particular star would appear to be very bright, but in no way brighter then the Sun even though it is between 1,800 and 2,100 solar radii (i.e. 2,100 times the size of the sun) and that it is also extremely bright with an absolute magnitude of -9.4, while the sun has one of only 4.85 (negative means brighter). However, were it to be one light-year away while the sun maintains its current position, the sun would still have a brightness of −26.74 while VY Canis Majoris would only have a -9.4, making it extremely bright but the sun would still be ~2.84 times brighter.



It wouldn't even be as bright as a full moon at −12.74.