Writer’s choice
Paper details:
Finding the Distance to Stars Using the Parallax Angle
This NASA web page provides additional explanation:
http://imagine.gsfc.nasa.gov/features/cosmic/nearest_star_info.html
Stellar Parallax is the apparent shift in the location of a star due to the orbit of the Earth. In other words, the star
will appear to be in a different place depending on the line of sight from the Earth. By knowing the diameter of
Earth’s orbit and by measuring the angle of apparent shift (the parallax angle), astronomers can calculate the
distance to the nearby stars using trigonometry. This method has been used for centuries. The ancient Greeks
were able to measure some of the closest stars this way. Today, sophisticated telescopes have greatly enhanced
this method.
Using a stellar astrometric catalog, we find that the two stars closest to HT Cas are a distance of 0.01 arcseconds
apart. Based on this information, we can estimate that the angle of shift of HT Cas (the parallax angle) to be
approximately 0.015 arcseconds apart. We also know that the radius of the Earth’s orbit is 1.0 A.U. (astronomical
units).
Using these two measurements, we can then determine the approximate distance to HT Cas using the following
equation:
d= distance to HT Cas
a=radius of the Earth’s orbit
p=parallax angle
1. Given the above equation and information provided, about how far away is HT Cas?
2. Your answer was calculated in parsecs. Given that 1 parsec = 3.2616 light years, about what is the distance to
HT Cas in light years? ( In parsecs X 3.2616 light years = The Distance to HT Cas in light years).
3. Based on your answer, do you think this is a star that we might be able to send a space probe to? Why or why
not? Support your answer.
4. Main Sequence stars can be classified according to which characteristics? What are the
characteristiÕÉ≠†Њ†cs of our Sun?
5 Which main sequence stars can be found with a surface temperature of between 3000K­4000K? Which stars
have a luminosity about 100 times less than that of the Sun?
6 Briefly describe the solar evolution time­line of a common star like our own from formation through collapse.